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NHL Mortar preparation: can be mixed in normal Mortar mixers.

Put approx two-thirds the amount of water, one third the amount of sand and all the lime followed by the remaining amount of sand and additional water until the required consistency is achieved. Mortar should be mixed for at least 10 minutes. Greater workability and better mortar performance is achieved with less water and longer mixing.(Mortars can be left to stand and fatten up for up to 1-3 hours depending on the mix: and tempered before use.)

Sand:  For building, pointing, base coats and coarse finishes on renders / plasters always use a well graded sharp sand free of silt and clay #10-20 mesh down to #No 200. For finer work: use a fine well graded sharp sand free of silt and clay #100-150 mesh down to #200. (In some circumstances where very fine sands are being used, less binder will be required).

St Astier Natural Hydraulic Limes can be used for a wide variety of purposes.

Typical mix composition.

Volume Ratios Cubic feet of Mortar produced Some typical applications
1 bag NHL5 : 1.5 bags of sand 2.9 Pricking up coat.
1 bag NHL 5 : 2 bags of sand 3.0 Coping,
1 bag NHL 5 : 2.5 bags of sand 3.8 Building / render / float / pointing
1 bag NHL 5 : 3 bags of sand 4.5 Building / render / float / pointing


Protection Protect from adverse conditions for at least 72 hours, longer if
conditions persist
Curing Fine mist spray as required
Caution Do not use in temperatures below 40 F or above 80F
Reworking/Tempering Can be tempered for up to 8 hours
Injection 1 bag NHL 5  10.5 Gallons of clean water. Mix with whisk.
If casein is used water content can be reduced
Gravity Feed 1 Bag NHL 5 :  + 16.9 Gallons (2.4 ft Cubic ft approx
) fine sand. Add water to required consistency


Main Rules : Do not over saturate with water, mix well, use well graded sands.

Re-Pointing Masonry Walls: Brick, Blocks and Natural Stone. 

Understanding mortars.

Before deciding to re-point a basic understanding of the function of mortars is required.   Mortar is used for jointing individual units in a mass of masonry. The final structure must have certain characteristics to function satisfactorily. It must carry the load for which it was designed, it must be durable and it must give protection against wind, rain, and frost. Mortar should develop sufficient strength and at such a rate as to be capable of withstanding the stresses to which it will be subjected during the construction of the building and subsequently when the structure is fully loaded.
It should not however set and harden so quickly that it becomes inflexible at any stage and cannot accommodate slight movement. There is normally no requirement for significant structural strength in the mortar of traditional masonry buildings, particularly in re-pointing work. Mortar should be permeable in itself, both so that the quantity of free water on the face of the building is reduced, thus reducing the possibility of wind-driven water penetration and so that moisture evaporation is not concentrated in the masonry, which may then be vulnerable to accelerated breakdown in the vicinity of the joints. Mortar should bond firmly to the units so that a tight joint is obtained through which rain will find it difficult to penetrate. Mortar should be workable, so that the material may be applied easily and to ensure that the vertical as well as the horizontal joints can be adequately filled.

Historic masonry buildings rely on their mass and the interlocking of individual units for their stability and the mortar in a masonry building serves in the main to provide a bedding for often very irregular components, filling the voids and maintaining the wind and watertight integrity of the building.

Choosing an appropriate re-pointing mortar.

Analysis of original bedding material is usually a good first step in determining the correct materials to use in the repair of historic masonry. Mortar can and does change with time, it is better that the analysis is carried out by a suitably experienced person or laboratory. It will not always be the case that simple matching will be sufficient. The exposure and condition of the building today may well be different from its original construction. Ruins and monuments in severe disrepair (i.e: lack of roofs, copings to wall heads etc…) might well require a repair mortar different from the original as the new mortar will have to cope with weather and exposure conditions for which the original mortar was not designed. Most important of all: the new mortar should be compatible with the old. Do not introduce mortars containing potentially damaging elements or that can constitute an impermeable barrier obstructing vapor exchange and retaining moisture. The consequences in a relatively short time could be disastrous and, in most cases, irreversible.

Resistance to salts

Soluble salts (sulphates, nitrates, chlorides) can be present in walls, they can be in the original mortar, in bricks and stones (often as a result of previous repair work), in ground water or from airborne pollutants. All St Astier NHL limes are resistant to salts. They do not contain the reactive components such as high levels of aluminium, potassium and sodium oxides and gypsum. Existing salts will therefore be allowed to migrate out of the structure without affecting the soundness of the mortar and, in time, be washed off.

Protection and good working practice.

For all lime mortar work, best practice requires proper curing and aftercare against the effects of drying winds, strong sunlight, rain and frost. Lime mortar may require slightly longer curing times but the methods and principles are the same. Where scaffolding is in place, fine mesh debris netting securely fixed to the outside of the scaffold gives basic protection to the working area slowing down strong wind while allowing good natural light for the works. In regards to external protection, the work should be covered with hessian sheets, polythene or both, depending upon conditions. Polythene should never come in contact with the work. To avoid rapid drying and consequent high shrinkage, especially in hot or windy weather conditions keep all work damp by repeatedly applying a fine mist of clean potable water, if necessary several times a day, until the mortar has hardened.


Starting from the top of the building, defective joints should be carefully cut out with appropriate tools and the joint thoroughly cleaned out, ensuring the inside upper and lower edges of the masonry are properly scraped clean of old mortar. In brickwork the joint should be raked out to 11/2 times the width of the joint or a minimum 3/4 of an inch. Ensure the back of the joint is square. The joints can be cleaned with a vacuum, low pressure compressed air and/or rinsed out with a garden hose to remove all loose materials: this is important as the mortar will adhere to dust which is left in the joints and deplete the bond. This is normally done form the top of the building down as the old lime in the mortar can stain the masonry if it is not properly washed of, working from the top down avoids unnecessary wetting of previously finished work. Prior to any re-pointing, controlling the absorption rate of the background is essential.


Mortar should be plastic and workable but as stiff as possible. It should be pushed into the back of the joints in layers, avoiding large volumes of deep filling at all times. On rubble elevations, pinning stones should be used to fill wide and deep joints in the same style as the original build. This will reduce the volume of mortar required and will assist the process of setting and final full carbonation. A good yardstick is to keep the joint thickness to no more than a “finger” thick, if the joints are wider than this they should be pinned with compatible matching masonry.


In natural stone masonry, to ensure good compaction and adhesion within the joint, the mortar can be tamped firmly back with a stiff bristle brush as it starts to firm up. The timing of this is critical. If it is carried out too soon after placing, fines in the mix will be drawn to the surface and will form a dense skin, inhibiting the proper curing of the mortar. Once the surface of the mortar is firm (usually the next day) lightly scraping the surface to expose the aggregate can improve the appearance of the mortar and make the joints less visible. This process should not be undertaken before the surface has stiffened or mortar will be smeared onto the face of the stone. A “well filled” joint is close to or flush with the surrounding masonry or to the weathered edge. Recessed joints define the masonry components and detract from the appearance of the wall, becoming a feature in themselves. Historically the common practice was to fully flush point and line out rubblework. Brickwork has a number of specific joint finishes too numerous to go into in this general guide, but the principles of timing the finishing of the joint still apply.

The fines in the mix will determine the finished color, therefore a wide range of natural colors is achievable without pigmentation. The whiteness of St Astier limes ensures the best color reproduction of the chosen aggregate.

Re-pointing dense impervious masonry.

Some masonries, such as granite, basalt, etc. and dense impervious bricks require special consideration. Due to their very nature of these materials have little if any, moisture absorption and therefore moisture is transferred to the joints. In these circumstances, the choice of mortar and method of application and finishing is very important. The joints are more vulnerable to the effects of wetting during placing and immediately afterward until a full set and carbonation have taken place. Using St. Astier NHL mortars will ensure setting without having to rely completely on carbonation. The stiffest mix possible should be used, avoiding free water in the joint cavity and consequent de-bonding effect.

The vapor permeability of NHL mortars will ensure moisture evaporation. Joints should be filled to flush, never recessed. Recessed joints will leave ledges for the accumulation of water that will keep the mortar joint wet for longer periods and accelerate the decay process. while feebly hydraulic limes were often used for the building of walls with impervious masonry the construction period usually left sufficient time for the joints to set up and cure before exposure to rain. Re-pointing is a much quicker process and more hydraulic materials are almost always a better option. Joints should be raked back to approximately 1″, thoroughly cleaned, including the top and bottom faces of the beds, ready for the new mortar. Pinning stones should not be removed, but if they are loose, they should be removed and put back during the re-pointing. Where a wall has previously been re-pointed and the pinning stones have been lost, suitable replacements should be used. The walls should be well washed to remove any dust and loose friable material making sure that the entire elevation is cleaned down to prevent staining on the walls. Impervious masonry should be dry when the work commences, however the original backing mortar should be kept damp.

Some re-pointing NHL mortar mixes

Very badly worn or damaged edges may require surface repair (see stone
repair mortar sheet
and subsequent tuck pointing to reduce the
visual impact of the traditionally very white ashlar mortars, and new joint
lines struck and pointed.

Joint type Joint size Pre-mixed mortar
(sieve size)
Lime  : Sand
Ashlar / Tuck joint 1/32″- 3/16″ Ashlar / Tuck pointing mix
or Ecologic F
#20 to #200 2 : 1
High porosity masonry 3/16″-3/8″ Ecologic™ G
NHL 3.5
#18-10 to #200 1 : 2 
1 : 2.5
3/8″-3/4″ Ecologic™ G
NHL 3.5
#6-3 to #200 1 : 2
1 : 2.5
Medium porosity masonry 3/16″-3/8″ Ecologic™ G
NHL 2  
NHL 3.5
#18-10 to #200 1 : 2
1 : 2.5
1 : 2.5 or 3
3/8″-3/4″ Ecologic™ G
NHL 3.5
#6-3 to #200 1 : 2
1 : 2.5
1 : 2.5 or 3
Low porosity masonry 3/16″-3/4″ Ecologic™ G
NHL 3.5
#18-10 to #200 1 : 2.5
1 : 2.5 or 3
3/8″-3/4″ Ecologic™ G
NHL 3.5
#6-3 to #200 1 : 2
1 : 2.5or 3
Interior Floor tiles or stone slabs 1/32″-3/16″ Ecologic™ F
NHL 3.5
#18-10 to #200 1 : 2
1 : 2 or 2.5
3/16″-3/8″ Ecologic™ F or
#6-3 to #200 1 : 2
Exterior Dense Paver Brick and Dense Stone Slabs 1/4″-1/2″ Ecologic LimeCrete-C Ready-Mix
NHL 5+ Special Cement Additive
1/4″-1/2″ Ecologic LimeCrete-C Field-Mix
NHL 5+ Special Cement Additive


This document is a guide only and is not intended to be a specification. Its purpose is to provide the reader with helpful information that may assist  in determining the correct choice of materials, methods of application and  determine the best working practice. The guidelines refer to our experience with St. Astier NHL binders and some recommendations might not be applicable to other products.

Using St. Astier NHL plastering mortars instead of non hydraulic putty mortars reduces the working time by about 50%.  NHL mortars offer similar vapor exchange qualities as putty mortars but are more robust, can be sprayed and  used for decorative plaster work without the addition of gypsum. Requiring less after care than putty, it can be applied in 2 coats on good level backgrounds.

Plastering in hydraulic lime mortar normally consists of two or three-coat work. Lime plaster made with feebly or moderately hydraulic lime and sand is the basis for this guide. This type of lime sets and hardens predominantly by an hydraulic set and re-absorption of Carbon Dioxide from the air. By its nature the drying and absorption process is slower than gypsum plasters, therefore lime plaster curing should not be hurried allowing approximately 3-5 days per coat depending on the
hydraulic lime used.

For plastering on the hard, the background will normally be brick or stone. The surface should be clean, free from dust and any organic materials such as lichens etc. Test the surface of masonry backgrounds for dust by applying a piece of masking tape to the background and immediately remove, examine the sticky side for traces materials that may affect the bond between the plaster and the wall.

Internal walls can be uneven and rough, often with areas that have been altered. Different background conditions are therefore common and this needs to be addressed before plastering. Deep holes, wide joints or pockets should be dubbed out in thin layers of mortar with pinnings tightly bedded in mortar, keyed and left to cure. The aim of preparing the background should be to achieve a surface that can take a first coat of consistent thickness, and to provide an adequate key for this first coat. The quality of preparation work is vital to the quality of the finished job. Suction between the first coat and the wall (and between all subsequent coats) is the primary means of bonding although a physical bond is also important. Different materials have different levels of suction, so for instance where a door way has been knocked through a stone wall and the edges built in brick, the brick may well have a different level of suction to the stone.  Understanding and controlling suction is important for successful work.

For wood lath and plaster work, laths should be fixed by butt and break joints to joists or battens securely fixed back to wall or ceiling, with gaps between the laths of approx, 8 – 10mm . The support battens or ceiling joists should be spaced so that the lath does not give unduly in the center. Wide spacing of battens or joists may require intermediate support or thicker laths. Sawn or riven laths (traditionally hand made) should be thoroughly damp before fixing. Dry laths swell when wet mortar is applied to them, sometimes causing the laths to bow in or out. Nails for fixing laths should be thin shank to avoid splitting the ends. Building paper and insulation is occasionally placed between laths and outside walls to comply with current building control requirements, this will have an effect on the drying rate and prevent proper rivet formation when fixed hard against the back of the lath. If building paper and insulation are essential, use moderately (NHL 3.5) or eminently hydraulic lime (NHL 5) for the first coat as they have faster natural sets, maintaining at least a 20mm gap between the paper and the lath.


First coat or Render coat:
Rendering stuff is made with NHL 3.5 or NHL 2 in a 1:2 ratio with well graded sharp sand 3.5mm down. Rendering stuff is mixed before use as described in the Making NHL Mortars data sheet. Hair or fiber reinforcement (if desired, but not necessary with hydraulic limes, except on lath work) is teased into the mortar and repeatedly chopped and turned until a good even distribution is achieved. The hair should be long and strong, free from lumps and clumps.Fiber reinforcement should be alkali resistant. It should be abundantly visible as a beard around the edge of an inverted trowel full of mortar.When working on the hard the first coat of mortar should be applied by throwing (a spray gun can be used) or with a laying-on trowel on to a dampened but not wet background at approximately 9 – 12mm thick (generally hair or reinforcing is not required on the hard). The render coat should not be straightened.For application onto laths, mortar should be trowel applied as evenly as possible and pressed home to form rivets between and behind the laths.The coat should cover the lath by approximately 8-10mm. Any initial shrinkage that takes place in the drying out phase, should be lightly floated back. Tighten the entire surface in with a cross grained wood float, closing back by further dampening and tightening in a close circling motion. Key the surface with a comb, or with a lath scratcher for plaster on laths, taking care not too score to deeply.In the case of lath work ensure that scratching is across, not in line with the lath.  Thereafter if necessary control the rate of drying out by misting the surface with clean water or lime water, until all shrinkage has stopped and the mortar has hardened sufficiently to receive the second coat. Do not over-wet the surface (if water droplets appear on the surface it is over-wet). Plastering on laths may take longer to dry as there is no suction of moisture into the background.Second coat or Floating coat
(this is the straightening coat).
Using the same mortar as the render coat and following the same method of mixing, apply with a laying-on trowel to a dampened background. At this stage, if straightening is necessary, fill out irregularities in thin layers and apply the floating coat to the desired line using rules or dabs.  Maximum thickness should be 12- 16mm in one pass. Tighten in as before with a cross grained wood float and key lightly to receive the finish. Any irregularities in the background must be made good at this stage as it will not be possible to straighten the finishing coat due to its thinness.


Setting Stuff or Finishing coat (hair is not required).
The finishing coat is made with NHL2 in a 1:1 with fine silica sand 0.8 to 0.075mm, clean and free from silt or clays. Better finishing will be achieved by re-working the setting stuff the day after. Apply with a laying-on trowel in two passes to an overall thickness of 2mm approx. Tighten in with a cross-grained wooden float, dampening as necessary as the set takes up.  Setting stuff sets by suction from the background. The final finish is produced by trowelling the surface with a steel float and dampening as necessary. Finish in one direction, usually top to bottom. Patching finished lime plaster into a repair requires care. The finish is sand based and will abrade and degrade existing edges leading to a dull surface around the repair. A clean break of a few mm is necessary around the patch and this can be filled later with NHL 2 made into a putty (no sand added) when the patch is fully hardened.Decoration:
Wallpaper or paint finishes should only be applied to fully dry and set work. Lime paint, limewash, distemper, and casein paints are traditional finishes for new work.Protection:
Work should never be undertaken in frosty conditions or where the temperature is likely to fall below 40oF during the execution of the work or until the mortar has hardened. Protection should remain in place for as long as possible (see data sheets on setting/curing times for individual limes).  Ensure that the rate of drying is consistent and that strong droughts are excluded from the working area.  This is particularly important where a building has windows removed or doors open. Never force the drying by introducing forced or excessive heating. If heating is required to maintain a proper working temperature use propane heating,this has the effect of producing both moisture and heat simultaneously. Ensure the temperature is adequately controlled.Good working practices:
Adequate preparation and protection are essential. Due care and attention should be applied to all work. Sample panels should always be done, allow sufficient time. See also Good working Practices within NHL Renders and Pointing with NHL

This document is a guide only and is not intended to be a specification. Its purpose is to provide the reader with helpful information that may assist in determining the correct choice of materials, methods of application and the best working practice. The guidelines refer to our experience with St. Astier NHL binders and some recommendations might not be applicable to other products.

Choosing the correct sand when making a mortar is of extreme importance.

Sands should be clean and uncontaminated by clay/silt. These occur in the range from #300 and below and the most effective method to establish their presence is the wet sieve analysis.

Normal dry sieve analysis does not accurately reveal the presence of clay or silt as they do not examine particles passing #200 sieve. Furthermore when the sand is dried before sieving, clay or silt particles can coat some particles and these will not pass the #200 sieve. In contact with water, however, these particles will return to colloidal state, retaining moisture and general instability. The result is a much longer drying period which, if winter is approaching, would not allow the mortar to be sufficiently dried to withstand frost.

The fines in a sand will demand more water. This is due to much higher surface area to be wetted. A high proportion of fines in sand and the consequent high water content in the mortar will have negative effects in compressive and flexural strength. High moisture will promote shrinkage and could lead to de-bonding especially in mortars applied to low suction areas.

There is a tendency to choose sands because of their color. The fact is that the color of a mortar will be given by the fines contained in the sand and therefore fine sands are chosen for a number of jobs where they are not appropriate.

In renders, for example, a good, well graded, coarse sharp sand is needed for the backing coats. A finer sand can be chosen for the finishing coat based on its color. If, however, the color of the sand is due to clay (earth) presence, as clay is a binder, the quantity of lime will be reduced to avoid producing a binder rich mortar.

Fine sands require more water. A high proportion of these sands lead to longer setting time, possibility of shrinkage, lime leaching and more sensitivity to adverse weather conditions.

Sands are mostly responsible for the void structure of a mortar and, therefore, for its vapor permeability, so vital for the performance against accumulation of condensation. It is for this reason that well graded sands are recommended. If sharp, the void structure will be even more efficient.

Monogranular sands (particle size mainly between 1 or 2 grades) will not allow good vapor exchange, they will also diminish workability and therefore increase the danger of too much water addition in order to achieve it. In making NHL mortars with good sand, workability should not be achieved by adding more water but by allowing a little more time for mixing. It is also advantageous, if time permits, to let the mortar rest for a while: the water will settle between the particles and allow better hydration of the free lime content resulting in a fatter, more homogeneous and workable mortar.

A practical guide to choosing sands:

particle size approximately 1/3 of the height of the joint
out: same sand as per base coat
Depending on the size of the joint, sands from 1/4″
down to #200 can be used, with a proportion from #100 to #200 about
20% of the mass.
coats, base coats and rough finishing coats:#7 down to #200 particles between #100 and #200 not above 15%
finishing coats#8 sieve (or less) down to #200. Particles between #100mesh and #200
sieve not above 20%
(% retained):

(% retained)

(% retained)

are a vast number of sands, differing in gradings and qualities. To be sure that
a well graded sand is being used it is necessary that at least 4 grades form a
substantial part of the proposed sand.

In rendering, sharp and well graded sands should be used for all coats.
For smooth finishes finer sand can be used, in which case this should still be well graded. The structural soundness of a render depends on the bonding with the background and between coats. Bonding is partly dependant on the capillary suction of the background or the previous coat. A percentage of finer particles (10-15% between #100 (0.150) and #200 (0.075mm) with 0 below
#200 (0.075)) will promote bonding without affecting vapor permeability and capillary suction.
Indoor smooth plastering will require fine sands. Particular attention should be given to curing.
Fine sands will also be used in ashlar work.

In all cases NHL binder quantities should be carefully considered and this should be done in relation to the performance required and the quality of the sand.

This document is a guide only and is not intended to be a specification. Its purpose is to provide the reader with helpful information that may assist in determining the correct choice of materials, methods of application and the best working practice. The guidelines refer to our experience with St. Astier NHL binders and some recommendations might not be applicable to other products.
Cob is a very simple (and efficient) form of construction that has probably been around forever in some form or other. Structures are formed of earth (normally of a high clay content), with some straw and sufficient water to make the mixture readily workable. The exact ingredients are prone to change along with the many different names given to the various techniques of earth building within the UK, depending on where you are in the Country and who you are talking to, yet they all follow the same, very simple principle which has often been tried and tested over many generations. Once built they are then often covered with some form of
protection, normally a render coat. *

* Note: Many earth structures were simply lime washed without a render, having received a good hat and a worthy pair of boots – (An adequate eaves overhang with a stone built plinth.)

Choice of materials
Given the yielding nature of the material used to create the building, the choice of binder is crucial to the performance of the render. Cementitious or non-breathable renders should be avoided at all costs. We only advocate a lime render onto cob and the following notes are offered as a general guide and not intended as prescriptive for all applications. The following is written with St.Astier NHL 2 (feebly) hydraulic lime or EcoMortar type F render in mind but are appropriate, in principle, to a non hydraulic (lime putty) render. We would rarely if ever, recommend anything stronger than an NHL2 for rendering onto cob. In the event of any queries regarding binders please do not hesitate to contact your St. Astier distributor for further guidance and advice.

The factors controlling a successful render onto cob will be preparation, and most importantly the control of suction, a detail requiring attention at all times. The cob will need to be reasonably sound and free of all vegetable matter, with a surface sound enough to receive a render coat. Very often cob that has been poorly protected is likely to be very soft and friable at the surface. Brush off this loose material. If necessary consolidate the surface by brushing on a lime water (NHL 2 or NHL 3.5 diluted 1:10 with clean water and applied twice at few hours interval).

Dubbing out:
Any depressions or hollows requiring dubbing out should be carried out using NHL2/sharp sand 1: 2 mix. Allow sufficient time to set, 4 days or longer if dubbing out is deep. Provide adequate keying to large daubed out areas.

Suction control:
At least 48 hours prior to the render application, a hose fitted with an attachment capable of delivering a fine mist spray should be used to quench the walls. Simply damping down will not suit as cob is normally a material capable of absorbing large amounts of moisture and if high suction is not controlled there will be a failure. The damping down should be carried out in a controlled manner using a cautious spray delivery at all times to achieve ‘even’ saturation over the whole area, without washing material out from the wall. Note: Over saturation can result in a ‘loss’ of bond for the render.



The initial dampening should be followed by as many further applications as appropriate, at least until there is a run off of excess water down the wall in the form of moisture beads. This pre wetting should continue right up to the application of render. There are no hard or fast rules as to the exact amount of dampening or the number of applications that will be required: too much is likely to result in a loss of wall material, with a reduction in bond for the render, too little will result in very rapid absorption of the mortar’s water resulting in de-bonding and cracking of the mortar. Either way, failure to address this issue from the outset is highly likely to result in a failure. Common sense is very much the policy for the dampening operation.Reinforcement:
It is often suggested that chicken wire or such like, should be fixed to the cob as a carrier for the render. We would advise against this, being of the opinion that it is totally unnecessary and technically incorrect. The render should be simply applied (cast on, harled) straight onto a well-prepared surface. However, we would recommend the addition of fibres or hair (for traditionalists) into the mix, as this will offer much improved tensile reinforcement to the render as well as helping to control cracking.

Over demanding structural cracks, where movement is likely, should be repaired before any rendering is attempted. An appropriate reinforcing net material in the render base coat placed over the repaired cracks can be used to good effect. This approach is very subjective with differing criteria or factors relevant to each situation and further advice should be sought from the appropriate source if it is a likely structural problem, or an unfamiliar technique.

Thickness of Render:
The thickness of the render should be determined by such factors as location, exposure and other relevant points that are likely to have a bearing. Different buildings will have differing criteria, with all factors requiring consideration prior to determining the render thickness. However, given that its function is to act as a protective, sacrificial coat to the earth construction, a sufficient thickness could be as little as a single cast on coat of 1/8″ – 1/4″ thick, using a St. Astier NHL 2. Cob can be placed under stress as a result of excessive loading from very thick render coats with a desire for flat and true surfaces something of a fools errand. Dubbing out, if necessary, should be carried out as preparatory work, with larger repairs carried out using cob blocks or other appropriate materials. Adequate time should be given to allow these areas to accept a render coat.


First Coat (bonding coat) 1 : 2 / Lime (NHL2) : sharp sand
The bonding coat should be cast or harled on, thus improving the bond between render and substrate, at a thickness of 1/8″ – 1/4″, well mixed to a consistency to suit the desired method of application (spray application is a stiffer mix than hand thrown). The grit in a good sharp sand will improve the keying in a cast on coat that has been left rough. Once applied this coat should be left to harden for a minimum of 3-4 days and protected properly to exclude direct sunlight and drying winds.


Second Coat (Undercoat/scratch coat) 2 : 5 / Lime (NHL2) : sharp sand

The scratch coat should not be applied for at least 3 – 4 days (or more, depending on atmospheric conditions) after completion of the first coat. Once again pre wetting is very important prior to application. If using a laying on trowel apply using firm and even pressure. The coat thickness should be even and once applied should not be overworked. In simple terms “lay it up and leave it alone.”

Thickness not exceeding 5/8″. Keying is best achieved by providing a crisscross pattern of a 2″
(or thereabouts) diamond pattern.

On completion provide adequate protective and curing measures. Any initial shrinkage taking place in the drying out phase can be dealt with by dampening the affected area and rubbing back using a plasterers wood float. This will need to be carried out within the first 24 hours. Pressing the float home evenly and firmly in a close circular motion. Re-key as necessary.

Proper protection, the addition of reinforcing along with regular humidifying (using a fog mist spray), will all greatly reduce the amount of shrinkage likely to take place.

Top Coat 2 : 5 / Lime (NHL2) : sharp sand or EcoMortar (premixed)
The most beneficial and traditional finish for cob is a roughcast (harling, spatter dash etc.) and this should be carried out by operatives skilled in this technique. A flat smooth finish (colored if desired) can be achieved using a normal NHL2 finishing mortar or EcoMortar F. The thickness of the final top coat is crucial and should not be applied any greater than 1/8″ – 1/4″.

Overworking mortars results in free lime and fines being pulled to the surface thus affecting the properties and visual appearance of the work.

Protect and cure for 7 – 10 days, longer if the weather dictates.

The choice of sand in the top coat is important, dependent on the finish required. A roughcast finish will require a grittier sand, smoother finishes require well graded fine sharp sands, silt and clay free (see also General Guidelines: Sands for NHL mortars.)

As for all NHL 2 renders, do not work in temperatures above 85oF or below 45oF and never when frost is forecast during the curing period.

Our document “General Guidelines – NHL Renders” contains further notes on protection and good working practice.

This document is a guide only and is not intended to be a specification. Its purpose is to provide the reader with helpful information that may assist in determining the correct choice of materials, methods of application and determine the best working practice. The guidelines refer to our experience with St. Astier NHL binders and some recommendations might not be applicable to other products.


Traditional ashlar jointing and bedding mortars were made with lime and crushed chalk, usually with a small amount of crushed stone or sand added for bulk. This was mixed on a marble slab with just enough linseed oil to grease the tools, it was made up into a consistency similar to stiff glazing putty, wrapped in oiled cloths and stored until required.

Material. Supplied in dry powder form in 5 gallon plastic buckets with re-usable airtight lids.
Ready for site mixing with clean drinking water and linseed oil (optional).

Background. Generally, natural stone (Ashlar blocks) or rubbing bricks, for building, or existing masonry for re-pointing. The background should be clean and free from loose or friable material, well washed to remove dust. Dampen high suction units. (Do not dampen very low suction materials such as granite)

Laying sawn six sided blocks or rubbing bricks.
Butter on to beds and perpendicular ends a full bed of mortar, firmly pressed into place to slightly more than the desired bed thickness and lay next block firmly in place to line and level by tapping firmly and repeatedly. Excess mortar will squeeze out. Leave excess in place for several hours.

Laying single faced masonry units.
Lay a ribbon of ashlar mortar (approximately 1″ in width) on the leading edge of the ashlar faced unit and a bed or normal coarse stuff to bed the irregular meeting faces. Tap down the stone to line and level, excess ashlar mortar will squeeze out. Leave excess in place for several hours.

The materials are firstly mixed dry to fully combine all the ingredients and just sufficient water is added to make the material into a dough like consistency, a good double handful size lump of the mortar has a thimble full of boiled linseed oil added and kneaded into the mix until it leaves the hands clean and is fully plastic. (Disposable
or rubber gloves are usually worn for this process). The mortar should be used within 24 hours, if being stored for more than an hour it should be wrapped in polythene to keep it moist. Because it is feebly hydraulic the mortar sets slowly but positively and on final set and full carbonation resembles hard chalk, matching exactly traditional ashlar jointing.

3281 linear feet of bed joints, at 3/32″ thick, and 4″ on bed requires 52 Gallons of mortar. Re-pointing 3281 linear
metres of 3/32″ thick joints at a depth of 3/8″: 5 Gallons of mortar are required.

See Pointing with NHL (re-pointing ashlar joints)

The above details are given for information purposes only. Final dosages and application should be checked with our technicians.
The Factory reserves the right to alter specifications

St. Astier NHL products for use with masonry cladding.
For the purpose of this document Masonry Cladding means thin sections of masonry each one fixed back to a frame or substructure or to themselves. The masonry will generally be between 1 1/2″ to 2 3/4″ thick.

Its main function will be decorative. Many cladding designs have units fixed in such a manner that normal masonry coursing and jointing is not part of the design and continuous perpendicular jointing is common.

Cladding can be laid on a bed of mortar or retrospectively jointed.
In many instances it is simpler to retrospectively joint the cladding as the bed width does not offer sufficient stability for the masonry to stand one unit on top of another and depends on fixing by mechanical means.

The design of the fixings will determine whether or not the construction can be built without movement joints. Fixings that have horizontal and vertical movement slots but provide lateral restraint usually allow walls to be constructed without movement joints, provided a mortar with a low modulus of elasticity is used.

The need for compressive strength in this type of work is not significant with a mortar of 150 – 300 at 28 days being usually adequate for the purpose.
NHL 2 and NHL 3.5 are very suitable binders for the production of cladding mortars. Their elasticity moduli is adequate in most instances and their free lime content, mainly responsible for plasticity, is high (25% and 50% respectively).

The above details are given for information purposes only. Final dosages and application should be checked with our technicians.
The Factory reserves the right to alter specifications
NHL5 1bag + 10.5gal of water
Capacity: 35 cu. ft./hr
NHL 3.5 1bag + 10.5gal of water
Pressure: 45 PSI.
NHL 2 1bag + 14gal of water

To these mixes an addition of casein can be made (1% of weight of the lime) to increase fluidity if so required. If casein is added the water addition can be reduced between 25% and 50%. Obviously NHL 2 mixes are more fluid than NHL 3.5 or 5

Use a non-cavitating whisk (1500/2000 revs per minute) to ensure total homogenization.


fine (01/02max)
1bag + 10.5gal of sand (55kg.approx) Enough
to obtain a paste with the required fluidity. Much less water is required if casein
is added.
NHL 3.5 1bag + 10.5gal of sand (55kg.approx)
NHL 2 1bag + 14gal. of sand (70kg.approx)

Casein addition is possible (see above).

Where open joints in the masonry show cavities, they should be marked as reference points. Point up open joints in masonry before grouting begins. Allow to settle and top up as necessary. Leave to cure for up to 3 or 4 weeks depending on the lime grout used before removing small areas of pointing to check the cavities are completely filled. Weep holes may be required to check the grout distribution.

The addition of casein will increase the compressive strength and the set whilst improving flow and reducing the water demand.  Shrinkage, already low in NHL products and mortars, will be further reduced due to the lower  water content of the grout.

This document is a guide only and is not intended to be a specification. Its purpose is to provide the reader with helpful information that may assist in determining the correct choice of materials, methods of application and determine the best working practice. The guidelines refer to our experience with St. Astier NHL binders and some recommendations might not be applicable to other products.
Lime Concrete for Floors, exposed aggregate / tamped finish

Ingredients. 10 x 66 lb bags (660 lbs) NHL 5 per cubic yard (or
27 cubic feet) of aggregates consisting of 1 part sharp sand: 2 parts
1/2″ to 3/4″ aggregate and approximately 3 to 3.5 gallons
of water per 66 lbs. of lime.
Mixing. Mix dry to achieve
a uniform color in a pan mixer or roller pan mill, slowly add clean water until
semi dry, just sufficient to allow mix to bind when squeezed in hand. Free fall
mixers can cause balling.
Substrate. Lime concrete should be laid on a compacted sub base
of clean 2″ to 3″ clean screened
aggregate (# 2 Stone)(minimum 6″ thick base). The greater the
thickness of the sub-base, the better the insulation properties. Damp
proof membranes are not necessary. Lime concrete can be laid directly
on to sub soils that contain clays that have had a 3/4″ layer
of NHL 5 hydraulic lime rotovated into them and compacted (sub soils
should be analysed before proceeding). Damp proof membranes are not
Laying. The concrete is placed in a single layer of 2″,
or 2 layers of 2″ to make a 4″ layer depending on purpose.
2″ will be sufficient for normal foot traffic and 4″ for
light vehicular traffic. It should be well rammed either by hand or
with a mechanical compaction plate to the desired level. Form mechanical
key between layers. Lay green on green (within 24 hours).
Finishing. Exposed
aggregate finish: after 24 hours the surface of the compacted and levelled concrete
is brushed with a stiff yard broom initially, then a soft brush. On large areas
it may be necessary to treat the surface of freshly compacted concrete with an
inhibitor to hold back the set.
A trial panel should always be done.
Curing Light
mist with clean water for 72 hours or more depending on conditions.
lay on a frosted or exceedingly hot surface. Protect from extreme heat, freezing,
excessive wind, strong direct sunlight and rain. Ambient temperature range should
40oF-85oFwith low to average humidity.
Protection. Foot
traffic should be avoided for 7 – 10 days depending on the weather. Cover with
protective walkways 12 hours after placing. These should remain in place for at
least 2-3 weeks or longer if possible.



Lime Concrete for Fine / ruled finish floors

Ingredients. 660lbs NHL 5 per cubic meter of aggregates consisting
of 1 Part sharp sand: 2 Parts fine sharp sand.
Mixing. Mix
dry to achieve a uniform color in a pan mixer or roller pan mill, slowly add
clean water until the correct moisture is achieved (semi dry) just sufficient
to allow mix to bind when squeezed in hand.  Free fall mixers can cause balling.
Substrate. Fine lime concrete finish should be laid on a freshly
compacted and keyed sub base of 2″ thick lime concrete made as
per exposed aggregate concrete.
Laying. The concrete is placed in a single consistent layer
of 3/8″ to 1″.  It should be well rammed either by hand
or with a vibrating screed to the desired level.  Lay green on green.
Finishing. Tighten
in the surface with a cross-grained wood float to a level plane, polish after
initial stiffening with a steel float if desired.  Lining out or ruling after
12 hours.A trial panel should always be done before attempting large areas.
Curing. Very light mist with clean water in drying conditions
for 72 hours.Protect from extreme heat, freezing, excessive wind,
strong direct sunlight and rain.  Ambient temperature range should
be 40oF-85oF with low to average humidity
Protection. Foot traffic should
be avoided for 7 – 10 days depending on the weather.  Cover with protective walkways
12 hours after placing.  These should remain in place for at least 2-3 weeks or
longer if possible.


Lime concrete sub base for slabs.

Ingredients. 5 – 66 lb or (330 lbs)NHL 5 per cubic meter of well graded sharp
sand #6 to #200
Mixing. Mix
dry to achieve a uniform color in a pan mixer or roller pan mill, slowly add
clean water until until the correct moisture is achieved (semi dry), just sufficient
to allow mix to bind when squeezed in hand.  Free fall mixers can cause balling.
Substrate. Outdoors: lay on a compacted sub base of clean 2″ screened
aggregate (3″ minimum).  Should a membrane be required use a
geotextile  (not polythene).
Indoors: lay on a compacted sub base of clean 2″ – 3″ aggregate
(4″ minimum).  The greater the thickness of the sub-base, the
better the insulation properties.  Damp proof membranes are not necessary.
Laying. Placed in a single layer of 2″.  It should be well rammed
either by hand or with a mechanical compaction plate to the desired
level.  Form mechanical key and lay a further 20mm layer loose ready
to set down slabs.  Lay slabs as normal.


 Jointing / Pointing mortar for slabs.

Ingredients. NHL5 at 1:2.5 with sharp concreting sand #6 to #200 for joints 1/4″
to 3/8″ wide.   Use fine sharp sand #16 to #200 for joints up
to 1/4″.  Avoid saturated sands.
Mixing. Mix
ingredients dry to achieve a uniform color.  Add: the minimum of water, the mortar
should be quite dry.
Placing Dampen
the joints of the slabs taking care not to wet the surface of the slabs, brush
mix into joints and compact with pointing key, clean all excess from slabs and
lightly dampen joints with clean water several times over a period of approximately
two hours depending on weather conditions.
Curing. Never
lay on a frosted or exceedingly hot surface.  Protect from extreme heat, freezing,
excessive wind, strong direct sunlight and rain.  Ambient temperature range should
40oF – 85oF with low to average humidity.
Protection. Foot
traffic should be avoided for 48 hours depending on the weather.  Provide walkways
with boards during and after placing to distribute any foot traffic/ loading.


The above details are given for information purposes only. Final dosages and application
should be checked with our technicians.

Vibrant and beautiful, the St Astier lime paint range is the perfect compliment to lime plaster, render and harling, suitable for most backgrounds. Can be applied to gypsum plasters, lining paper, cement and lime backgrounds, bricks, blocks and untreated timber.

Mixing: The general ratio is 1 volume of powder to 2 volumes of clean water. Further dilution might be necessary on porous backgrounds. The lime paint is supplied in tubs as a powder for mixing on site with water. The tub has a fill line for normal use. Proper mixing is essential. When mixed it should be completely free of lumps or fine particles. Best to let sit with lid on for 24 hours before use. Check the bottom and sides of the mixing tub to ensure all the powder is fully combined. This ensures that no lumps or fine particles remain and are fully dissolved throughout the lime paint.

Application: Do not work in temperatures below 40oF or above 85oF or in a humid environment. Protect painted areas from direct sun, drying wind and rain for 3 to 4 days (longer in damp weather conditions). Do not use warm air dryers. All new rendered or plastered surfaces should be properly dry before applying lime paints.Apply with a good quality long hair brush in short strokes. Evenly and thinly spread the lime paint on the surface, work into any small hollows or cracks. Do not overload the brush, use only the bottom third of the bristles, do not apply unevenly. Stir regularly during application. Generally 2 coats are sufficient. Wait 12 – 24 hours between coats. On large areas of work, always keep the working edge damp, do not allow the lime paint to dry out and form a dry joint. Inadequate protection of the working area will exacerbate drying. Maintain a dampened background in advance of application with a light mist spray if necessary. Sufficient personnel should be used to complete large areas without forming dry joints. Always finish whole walls or elevations into details, angles, corners, down pipes or the like in one operation to avoid color banding. St. Astier Lime Paints can be sprayed: please consult your Supplier.

Background: Remove any loose or flaking paints and repair defective plasters or renders. Test the background for suction by lightly flicking clean water from a brush on to the surface of the wall.  Rapid suction into the background means that dampening with clean water will be required. In this case it may also be necessary to thin the first coat with 30% additional water. If thinning is required mix as normal then take out with a measured container the quantity you require to be thinned, place it in a separate container and add the extra water. A low suction background does not require pre-wetting or additional thinning for the first coat.

Very smooth or polished surfaces offering little or no suction might require sanding down with sand paper to create the necessary suction.

Ensure that background is dry, clean and sound. Do not use lime paint in areas subjected to abnormal condensation such as a kitchen or bathrooms, unless sufficient ventilation is available to prevent condensation.  Lime paints are not film-forming materials that will hide the background condition therefore salts and dampness will show through. Some surfaces may have variations in background materials (i.e.: brick, stone, cement, etc) and therefore care is required in controlling differing suction levels.Due to the additives content of some modern gypsum premixed plaster there may be some reaction with lime paints. Furthermore gypsum plasters tend to be extremely smooth and therefore would need to be lightly sanded down to provide a suitable surface before applying lime paint.Wallpaper joints are often smeared with adhesive during hanging. Make sure that the adhesive paste used is water-soluble. Clean the joint before applying lime paint, as excess adhesive residues on the face of the paper will cause the lime paint to dry out a different color.

Recommendation: If in doubt, always try on a small test area.

Unsuitable backgrounds: Not to be used on backgrounds with no suction or containing waterproofing agents, oil paints, grease, distempers or cement paints which have water repellent agents.

Protection: Do not use below 40oF or above 85oF. Avoid working in foggy/ damp weather. Protect from rain, strong direct sunlight and drying winds for at least 24 hours or longer if required.

Technical data: Made from pure high calcium hydrated lime. Acrylic addition: max. 5%. Pigments: mineral or earth oxides. Normal dilution ratio –  1 vol. powder: 2 vol. water (1kg. Powder: 4 litres water)

Shelf life: Powders: 12 months from purchase date if kept sealed in original container. Once mixed with water: 24 months if kept sealed in airtight container.

Health and Safety: Irritant to the eyes and skin. Wash affected areas abundantly with clean water (do not use soap).  Do not ingest or inhale dust. Wear adequate protection (mask/goggles/gloves) during handling and mixing.

Recommendations in this document are for general guidance purposes. For job specific advice please consult your local St Astier Distributor
NHL Renders

General information
Sands for renders
Background preparation
Two coat work
Three coat work
Good working practices
Render Diagnostics
Some recommended mixes


Other General Guidelines documents:

Render on cob
Render on wooden lath
Render on metal lath
Render on blocks
Rendering with a spray gun

The correct specification for any render should consider the nature and condition of the background, site exposure, time of the year (weather maps / rainfall and wind driven rain indices) and type of finish required.

The success of a render depends on ensuring good background preparation and suction control, the correct choice of a mortar and its application. Sample panels should always be carried out. The durability of a render depends on mortars that will adhere to the background, are able to breathe and resist harsh climatic conditions that can and do occur even in relatively benign climate zones. A good bond to the substrate and between all coats is essential to the soundness of the render structure. Bonding is both physical and mechanical:

A physical bond is achieved by controlling the suction correctly, such that a suction bond develops. The natural surface condition can also offer a good key.

Mechanical bonding is induced by the method of application. Ensuring good keying between layers, and especially the first coat, by casting/harling or spraying is by far the most successful method.

To avoid potential de-bonding and cracking each coat should be not be richer in binder or thicker than the preceding one (thicker base coats are applicable on thin stipple/scratch coats).

Sands for renders.
In dubbing out, stipple coats and base coats the sands should be well graded, washed and free of clay/silt (particles below #200 mesh). Use sharp sands from #6 down to #200, with the bulk of the sand in the #16 down to #100. Fine sands or monogranular sands (bulk in 1 or 2 grades only) are to be avoided.

In finishing coats, finer sands, still well graded, can be used for smooth finishes (avoid overtrowling). Particular attention will have to be paid to finishing coats with fine sands to avoid high shrinkage due to the high amount of water that fine sands absorb. The use of a wooden float, energetically applied in small circular motions, will help. Floating with plastic floats is not suitable. Sponge floats can be used after the wooden float work is completed to achieve a particular texture in the finish. Curing will also be important. Small hairline shrinkage cracks can be healed if treated in time with a light water mist.

Note: the finer sand particles are the ones mostly responsible for color and therefore used for color rendition. If the fines denote presence of clay (particles below #200 mesh) the NHL binder quantity should be reduced (clays are also binders!). A wet sieving analysis is recommended to check clay / silt content.

Background Preparation:
Check that any movement cracks are stable and where necessary ensure they are properly tied and if needed,
grouted/pinned/pointed. Careful removal of existing renders will result in less remedial repairs prior to re-rendering. Removal of failed or inappropriate existing render or finishes, including many types of paint, may require the walls to be left to dry out properly before re-rendering and time should be allowed for this. Ensure all repairs to the background are completed and that loose pinning stones or defective bricks are repaired or replaced prior to commencement of any rendering. Partial or complete re-pointing / consolidation may be required. Remove all loose and friable materials, remove and treat all organic growth, use biocides where applicable, ensuring that they will not affect the mortar.Newly built walls should be allowed to dry properly, usually 1 month. This will not take place readily in winter conditions.Repointing before rendering:
If this is necessary it should be done with a compatible mortar.Detailing:
Inspect all details, i.e. copings etc. Check gutters and down pipes and all forms of roof drainage, ground drainage and general ground conditions. Make sure all the above items are functioning properly and where remedial action is required, ensure it is completed before proceeding with render work.Rendering should never come into contact with soil. Renders should be kept clear of the ground or finish at the base of a wall into free draining gravel.Dubbing out:
On defaced surfaces or in areas with a large amount of damaged joints it will be necessary to apply a dubbing out coat to provide a level surface. In most cases this will be sufficient with mortar, however very deep joints or hollows should be pinned to reduce the mass of mortar. When a dubbing out coat is used, let it set sufficiently (8-10 hours) before scraping it and keying it. Apply the first coat after approx. 2 days (more if very deep recesses have been filled) and depending on weather conditions. Dubbing out should leave a relatively flat surface, keyed as necessary, on which to render.Suction control:
If needed, apply sufficient water to reduce excessive suction, especially on bricks and porous stone. Old bricks often require more water than new ones. On many occasions this is done the day before, if necessary several times with the last damping just before application starts. Apply water starting at the top of the structure. Over saturation of the background will result in loss of bond. Never render backgrounds that have standing water on the surface. Always dampen preceding coats before applying next coat.It should be noted that in the presence of different suction levels the degree of dampening will vary accordingly.

Provide adequate keying between background and base coat and between each coat. Crisscross patterns are preferred to
combing. Make sure that keying does not cut too deeply. Sometimes joints in brickwork are raked back (normally 1/2″), this is not necessary with NHL renders if a stipple coat is applied cast on, harled or sprayed on.Two coat work 
Two coat work is suitable for renders with an overall thickness of approx. 5/8″ on surfaces that provide adequate suction and a good key. On surfaces offering poor suction and keying, it is recommended to use a stipple coat (1/8″-1/4″ thick) applied by casting on, harling or spraying. The main coat can be applied after sufficient hardening and finished as required. Alternatively use 3 coat work by applying a finishing coat.On two coat work the base coat will be the thickest (up to 1/2″, more if applied in 2 passes) and with a binder: sand ratio of 1:1.5 or 1:2. Use mainly NHL 5 or NHL 3.5. This can be laid on or preferably cast/sprayed on. Scour back and key after initial setting.
To ensure a flat and uniform surface see “Ensuring a level surface” under Undercoat in 3 coat work section.Curing:
Check for initial shrinkage. If found, dampen surface lightly with water and tighten back and re-key. Repeated shrinkage is usually a function of poor quality sands, poor suction control or rapid drying.Finishing coat:
Use NHL 3.5 or NHL 2 (see individual product sheets)
3/16″ max. for smooth or light textured finishes, 5/16″ for coarse finishes (tyrolean, roughcast etc…).Smooth and light textured finishes:
Use finer well graded sands, #14 down to #200 mesh. Add just enough water to obtain required workability. The more water is added the higher the risk of shrinkage. When the mortar is firm enough, proceed to float up with a cross-grained wood float. This
is the most important phase of the finishing work and should be done diligently. Together with good curing and protection it is vital in obtaining a good finish.Coarse finishes:
Use coarser sands if thick (rustic) granular finishes are required. The thickness of the coat depends on the final finish required. Some of these finishes, especially the ones requiring special skills such as cottage, scraped and travertine effects, could also be done by using the same type of sand as smooth and light textured (floated) finishes. In these and tooled renderings (patterned), if initial shrinkage takes place, lightly dampen the surface and re-float the area during the first day or two. Tooling is normally applied when the render is 5-7 days old.

Two coat work (contd.)
Dry dashing:
Throw the chosen aggregate onto soft mortar and leave exposed. To speed up the work a plasterer
throwing the aggregate can follow the laying on plasterer.
Curing by water mist over 3 to 4 days, if necessary more than once a day, is essential when weather
conditions would cause quick drying. Always protect the work from adverse weather conditions.
Three coat work
Background preparation, sands, suction control, keying and dubbing out: as previously described.

First coat:
Has to provide sufficient bonding. Stipple or spatterdash can be used on all backgrounds, but especially on impervious and smooth background. Leave these coats rough to provide a key. Use richer mix (1:1.5 preferably). The normal thickness is between 1/8″-1/4″. On soft or weak background use 1:2 or 2:5. Successive coats must be weaker than this coat. The thickness of the first coat depends on the nature of the background and the overall thickness required of the render.

A laid on scratch coat can be used on old bricks or surfaces providing a good key (greater care is required in application to ensure good bonding with the background). It will be scoured back with a cross grained wood float and keyed (crisscross keying pattern preferred) once initial stiffening has taken place.

Second coat (straightening):
To be applied 2 days (or more, depending on weather conditions) after completion of first coat. Its strength should be less than the first coat. Thickness will vary according to the overall thickness required but it is normally between 1/2″-5/8″. It must not be over 3/4″ thick. If this is required it should be done in successive coats each not exceeding 3/4″. The thicker the intermediate coats, the longer the waiting time before each subsequent application.

Ensuring a level surface:
To achieve a uniform and level surface fix vertical timber battens or dab’s on the wall at 6-8 feet intervals. If the wall is uneven use spacers and check that battens are straight with a plumb level. Fill out to screeds, if necessary in layers. Screed off excess mortar between battens with a wooden straightedge spanning between the battens. When battens are taken down, fill in strips with the same mortar.

An alternative is to make running screeds 4″ wide at regular intervals.

Scour back and key as usual after initial setting. Check for shrinkage during the first 2 days and, if necessary, lightly dampen the relevant area, tighten back and re-key. In case of intermediate coats this would apply to each coat. Do not apply finishing coat until undercoat is adequately hardened.

Three coat work (contd.)

Finishing coat and curing:
As per 2 coat work.Protecting NHL mortars and renders
The setting properties of NHL mortars require protection against adverse weather conditions. Precautions are necessary and, if in doubt, your St. Astier Distributor will be able to advise further. The following are the main recommendations:

Mortars made with
Protect from frost, rain, strong wind or direct sun for minimum
48 hours
NHL 3.5
72 hours
96 hours

Early exposure to rain will cause some moisture absorption in the surface of a fresh render. If frost occurs, there might be damage. The figures given above refer, therefore, to a render that has not been subject to water  penetration in its early life.

The preferred form of protection is burlap covers that, with re-damping, will also contribute to curing the mortar. Burlap covers are essential to protect against frost. Plastic sheeting is effective against rain but should be kept clear of fresh work. If too tight it will generate condensation leading to unsightly staining. It will not protect against frost. Frost protection should be provided even if frost is not occurring at the moment of finishing the day’s work but is forecast during the early days of a mortar. Work should not start in frost conditions or when frost is forecast or with temperatures below 40F. In working with NHL 2 or in rendering with fine finishing coats, this should be 45F. Protection from the quick drying effects of wind or direct strong sun should be provided by using shading sheets on scaffolding.

Good working practices
In this document we have already discussed items such as background preparation, suction control, detailing, keying, protection and curing. A good and durable result depends mainly on these factors, the correct mortar mix, sand, dosages and workmanship. One item not to be overlooked is scaffolding. Where scaffolding is being used make sure that the scaffolding has adequate clearance from the face of the wall to allow application, avoiding unsightly lift lines. Scaffolding should project past all areas to be rendered to allow for protection of the new work against direct rainfall. Generally scaffolding should be capable of carrying the protective screens necessary to shade the work and prevent rapid uncontrolled drying and any covers needed to protect against frost.

This document is a guide only and is not intended to be a specification. Its purpose is to provide the reader with helpful information that may assist in determining the correct choice of materials, methods of application and determine the best working practice. The guidelines refer to our experience with St. Astier NHL binders and some recommendations
might not be applicable to other products.

Shrinkage & Cracking
greater than 1/16″
General or partial movement of the background
or the building.
Check if movement is still active. (Engineer to check). If building stable, repair cracks / areas.
Shrinkage & Cracking
less than 1/16″
Thermal movement.Poor workmanship. Render too thick. Too much water in mix. Over saturated backgrounds. Insufficient setting between coats. Depending on extent, open out crack and fill with same mortar.
Hairline cracks Bad preparation of background. Over saturated background. Too much binder. Too many fines in sand. Finishing coat to thick.Too much water in the mix. Rapid drying / lack of protection. Too much sun or wind during curing. Either apply slurry fill if sound or remove and replace properly.
Loss of Bond Poor background preparation. Poor suction control. Over saturated  background. Background too smooth. Incompatibility with existing background. Insufficient strength in bonding coat. Background movement. Metal corrosion. Salt crystallisation. Excessive or late towelling. Repair or replace as appropriate. Consolidation by grouting may be considered.
Bulging Poor background preparation. Incompatibility with existing background.Metal
corrosion. Frost damage during curing.
Depending on the extent of damage, either partial repair or total replacement. Neutralize and  treat any rusting metal.
Powdering / Friability De-calcification of render (loss of binder). Poor background preparation. Poor suction control. Rapid evaporation of water during application, (prior to adequate set). Frost  damage. Insufficient binder dosage. Variation in surface compaction / finishing. Poor sands. Partial or total repair with correct mortar applying due protection and following best practice.
Water penetration. Poor background preparation. Weak mortars. Bad detailing. Partial repair. Light repairs with several coats of lime wash.Rectify
detailing problems. Replace if necessary.

Prepare background
Re-point and dub out as necessary with compatible mortar.
Stipple Coat Cast or sprayed on only
Must be used on poor suction, dense / smooth surfaces.
Leave as Cast
Cure 2-4 days
First Coat
Cast, spray or lay on.
Well-keyed background.
Control suction. Leave Keyed
Cure 4-7 days
Second Coat
Cast, spray or lay on. Control suction. Straightening
Leave keyed. Cure 7-10 days. Finishing coat in 2 coats work.
Cast, spray or lay on.Control suctionFinish as required
Cure min 3-10 days
Cob / Earth Mix 1A – Sand SG
Mix 1B – Sand SG
Mix 1C – Sand SG
Mix 1C – Sand SF / FS
Wooden Lath Mix 2B/3B – Sand SC
1/2″-5/8″(1/2″ cover)
Mix 2C – Sand SC
Mix 1C – Sand SF 1/8″-1/4″ Mix
2C – Sand SM 1/2″-3/8″
Metal Lath Mix 3B – Sand SC1/2″-5/8″ (1/2″
Mix 2B – Sand SM 1/2″-3/4″ Mix 1C – Sand SF1/8″-1/4″Mix
2C – Sand SM1/2″-3/8″
Soft Brick / StonePorous Blocks Mix 1B – Sand SC3/8″-5/8″ Mix
2B – Sand SC3/8″-5/8″
Mix 1B/C – Sand SC/SM3/8″-1/2″B/C
– Sand SC/SM3/8″-1/2″
Mix 1C – Sand SF1/8″-1/4″Mix
2C – Sand SM1/2″-3/8″
Medium Brick / Stone / Blocks Mix 2A/3B – Sand SG*1/8″-1/4″ Mix 2B/3C – Sand SC 1/2″-3/4″Mix
2B/3B – Sand SG**3/8″ -5/8″
Mix 2C/3D Sand SC/SM5/16-1/2″ Mix
2C/3C Sand SG**1/4″-1/2″
Mix 1C – Sand SF1/8″ -1/4″ Mix
2C – Sand SM1/2″-3/8″
Dense Brick / Stone/ Blocks/ Concrete Mix 2A/3A -Sand SG1/8″-1/4″ Mix 2B/3C – Sand SC1/2″-3/4″Mix
2B/3B – Sand SG**3/8″-5/8″
Mix 2C/3D Sand SC/SM5/16-1/2″Mix
2C/3C Sand SG**1/4″-1/2
Mix 1C – Sand SF1/8″-1/4″Mix
2C – Sand SM1/2-3/8″
NHL binder : sand mixes (by volume)
* Stipple coat optional, depending
background suction and conditions.
** For harling (thrown) applications.Note: a wide variety of finishes can be achieved by adopting different
binder and sand mixes to satisfy all requirements.Coat thickness and optional mix ratios are related to exposure and background
conditions and are the responsibility of the designer.Curing and protection must follow best working practice.
Lime Mix A
Mix B
Mix C
Mix D
Mix E
NHL 2 1A 1B 1C 1D 1E
NHL 3.5 2A 2B 2C 2D 2E
NHL5 3A 3B 3C 3D   
Sands Type Particle sizes (Mesh)
SG Sharp gritty #4 down to #200
SC Sharp coarse #6 down to #200
SM Sharp medium #8 down to #200
SF Sharp fine #16 down to #200
FS Fine soft #20 down to #200
This document is a guide only and is not intended to be a specification. Its purpose is to provide the reader with helpful
information that may assist in determining the correct choice of materials, methods of application and the best working practice. The guidelines refer to our experience with St. Astier NHL binders and some recommendations might not be applicable to other products.
This method is particularly suitable to ensure optimum bonding even on smooth surfaces. Spraying is recognized as the best method of application allowing sharper sands and lower water content in the mortar mix. The speed of work is considerably increased and an average of 1000 square feet per day per man is quite normal. The pressurized application also allows to build up the thickness of a layer to 1″. The pressure should not exceed 3.5 Bar*. Two coat work is normally sufficient with the use of a spray gun.
Overall render thickness
3/4″-1″ 1″-1 3/8″ up to 1 9/16″
On surfaces with low keying (for thickness above 1 9/16″
please consult us.)
Stipple coat
NHL 5 or NHL 3.5 @ 1: 1.5
Sands: well graded 5mm down to 0.075
1/8″- 3/16″ 1/8″-3/8″ 3/16″-5/16″
Leave 24/48 hours as sprayed to provide good key
1st coat
NHL 3.5 @ 1:2 or NHL 5 @ 1:2.5
Sands: well graded 3mm down to 0.075
3/8″- 5/8″ 3/8″-5/8″ 3/4″-1″
Leave for a minimum of 4 days depending on weather conditions, coat thickness and the plasterer’s judgment.
Level using a straight edge and key with criss-cross pattern.
If this is also the finishing coat (3/4″-1″), depending on the finish required, a finer sand can be used (#6 to #200 mesh).
2nd coat (finishing coat) 3/16″-5/16″ 3/16″- 3/8″ 3/16″-3/8″
NHL 3.5 @ 1: 2.5 or NHL 2 @ 1:2
Sands: #6 mesh down
Finer sands for wooden float or smooth finishes (#8 or finer) can be used. In these cases the thickness should not be over 3/16″.
Notes: background preparation as per good practice. Always dampen surface before each application. On high suction background ensure that this is thoroughly dampened (no standing water on surface), if necessary several times, to minimise shrinkage. Cure work for few days with water mist. Protect against rain, frost, drying wind and direct sun for 2 to 7 days. If dubbing out is required the mortar ratio should be the same as the 1st coat. Leave dubbed out areas as sprayed to provide a key.*Sablon S3 Hopper gun


Overall render thickness
3/4″- 1″** 1″-1 3/8″ up to 1 9/16″
On well keyed surfaces.
(raking joints not necessary)
(for thickness above 1 9/16″
please consult us.)
1st coat
3/8″- 5/8″
NHL 5 or NHL 3.5 @ 1: 1.5
Sands: well graded #4 down to #200 mesh
Trowel off high spots and leave 3-4 days as sprayed
to provide good key.
2nd coat 3/16″- 5/8″ 3/8″- 5/8″ 3/8″- 5/8″
NHL 5 @ 1:2.5 or NHL 3.5 @ 1:2
Sands: well graded #6 mesh down to #200
This can be the finishing coat for a 3/4″- 1″ render. If a smooth finish is required apply a 3rd coat as below. Level using a straight edge and key with criss-cross patterns.
Leave about 7 days depending on weather conditions
and the plasterer’s judgment.
3rd coat (finishing) 1/8″- 3/16
Smooth finishes only
otherwise use 2nd coat
as finishing coat.
3/16″- 5/16″ 3/16″- 5/8″
NHL 3.5 @ 1: 2.5 or NHL 2 @ 1:2
Sands: depending on the finish required.
Finer sands for wooden float or smooth finishes (#8 or finer) can be used. In these cases the thickness should not be over 3/16″.
** This thickness can be achieved in one coat
(several passes) with suitable aggregates. Please consult us.
Notes: background preparation as per good practice. Always dampen surface before each application. On high suction background ensure that this is thoroughly dampened (no standing water), if necessary several times, to minimize shrinkage. Cure work for few days with water mist. Protect against rain, frost, drying wind and direct sun for 2 to 7 days. If dubbing out is required the mortar ratio should be the same as the 1st coat. Leave dubbed out areas as sprayed to provide a key.


The information provided in these pages is of general nature only and does not constitute a full specification.
Dig Deeper

Research Papers

Explore our list of reference articles from leading scholars, architects, and researchers.
- by Wei Luo

Evaluation of Comparative Repair Methods for Stone

- by S. Barr, W.J. McCarter, B. Suryanto

Bond-strength performance of hydraulic lime and natural cement mortared sandstone masonry

- by A. Miltiadou-Fezans

A multidisciplinary approach for the structural restoration of the Katholikon of Dafni Monastery in Attica Greece

- by L. Tedeschi, technical director, C.E.S.A.

Risks associated with the use of GGBS for the manufacturing of Artificial Hydraulic Limes

- by A. Kalagri, A. Miltiadou-Fezans and E. Vintzileou

Design and evaluation of hydraulic lime grouts for the strengthening of stone masonry historic structures

- by L. Tedeschi, technical director, C.E.S.A.

Risks associated with the use of GGBS for the manufacturing of Artificial Hydraulic Limes

- by Jennifer Schork, Norman R. Weiss, and John J. Walsh

Comparative Laboratory Evaluation of Conservation Mortars

Self Healing Capacity of Lime Mortars

Decay Mechanisms and Salts

- by Philip D. Allsopp, D.Arch., RIBA & Lauren Allsopp, Ph.D.

Lime and its Place in the 21st Century

- by Lauren B. Sickels-taves, Ph.D.

Selecting Mortar for Historic Preservation Projects

- by Gérard P. Michon

Permeability and Permeance: Vapor barriers and porous materials

- by John Ashurst

The Technology and Use of Hydraulic Lime

Water Reduction Studies of Natural Hydraulic Lime

Mineralogy of Binders and the Effects of Free Lime Content and Cement Addition in Lime Mortars

- by Plamen Ivanov Peev

Is industrial hemp a sustainable construction material?

- by Jackson ET AL.

Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete

- by Asi Shalom

St. Astier NHL 5 plasters and mortars for high salt saturated historical buildings

- Joseph Bacci

The Influence of Fire and Water on Lime, Natural Hydraulic Lime, and Cement-Lime Mortars


Common Bond in BrickworkUpper: Modern, stiff mud, wire cut standard 7-5/8 face brick pointed with mortar struck flat or as a flush joint to show aggregates.

Mortar Mix: 1 part Ecologic™ Mortar G #DGM 200 (brown/grayish) 2lbs washed coal flecks, (or medium grade slag flecks). (2lbs)


Lower: Historic, stiff mud, wire cut smooth Philadelphia Brick, an 8-1/4 face brick with Buttered joint.

Mortar Mix: Use either Ecologic™ Butter Joint premix or 1:2 mixture of NHL 2 to Marble Dust by Volume 1/4 part marble dust screenings.

Finish Tools – 3/8″ slicker, 1/8″ slicker, 1/16″ slicker

Carolina variegated sandstone pointed in a Beveled Ridge jointMortar Mix: Ecologic™ Mortar G #DGM 50

Finish Tools- 3/8″ slicker, 1/2″ slicker

Variegated siliceous Iron stone pointed in a Raised and Ruled White Ribbon joint over a neutral colored background mortar brushed flatUpper: Modern, stiff mud, wire cut standard 7-5/8 face brick pointed with mortar struck flat or as a flush joint to show aggregates.

Mortar Mix: 1 part Ecologic™ Mortar G #DGM 200 (brown/grayish) 2lbs washed coal flecks, (or medium grade slag flecks). (2lbs)


Lower: Historic, stiff mud, wire cut smooth Philadelphia Brick, an 8-1/4 face brick with Buttered joint.

Mortar Mix: Use either Ecologic™ Butter Joint premix or 1:2 mixture of NHL 2 to Marble Dust by Volume 1/4 part marble dust screenings.

Finish Tools – 3/8″ slicker, 1/8″ slicker, 1/16″ slicker

Diopsidic sandstone (Serpentine-like (green) pointed in a Cobweb Ribbon (cobweb also Serpentine-like (curves)!)Mortar Mix: Ecologic™ Mortar G #DGM GREY

Finish Tools- 1/2″ slicker, Wire Duster and 1/2″ ribbon jointer and a loop.

Limonitic sandstone (yellowish brown) pointed in a Grapevine Stone joint, (not to be confused with the commonly named grapevine joint in brickwork where in that case an incised 1/8 line is impressed into the wet mortar when striking with a grapevine jointer tool.)Mortar Mix: 1/2 part Ecologic™ Mortar G #DGM 100 1/2 part Ecologic™ Mortar G #DGM 250 (greenish ochre-brown colored).

Finish Tools- 1/2″ slicker, 1/2″ Stone Grapevine Jointer

Appalachian Bluestone (a sedimentary sandstone) pointed in a **Beveled Ridge joint which had the yellow sand aggregates exposed for a weathered appearanceMortar Mix: 1 part Ecologic™ Mortar G #DGM 100 (light brown/mud colored) 2lbs yellow concrete sand (Inclusions of lime chunks were also added along with the sand aggregate to duplicate the imperfection often seen in weathered mortar where the original lime slaking left bits of calcium hydroxide not fully broken down in the putty and where weathering reveals such bits. This denotes a “hot mix was used and fresh slack lime had sand added then used immediately). Mix NHL 5 and water, let it harden a week and break it up to add small bits.
Exterior, weathered, (by exposing aggregates) brown coat plaster (AKA stucco, render). Inclusions of lime chunks (see note above) were dashed into the wet plasterMortar Mix: 1 part Ecologic™ Mortar G #DGM 100 (light brown/mud-colored) 2lbs brown concrete sand.

Tools for Panel 6- 3/8″ slicker

Tools for Panel 7- Stucco and Harling trowels, Churn brush and garden hose with water to expose aggregate the next day.

Pennsylvania’s Rockhill Granite, (trappe rock), pointed in a **Beveled Ridge joint which had the reddish/brown sand aggregates exposed for a distressed and weathered appearanceMortar Mix: 1 part Ecologic™ Mortar G #DGM 100 (light brown/mud colored) 1-3/4 lbs brown concrete sand 1/4 lb medium grade slag flecks.

Finish Tools – 1/2″ slicker, Churn brush and garden hose with water to expose aggregate the next day.

Philadelphia’s Chestnut Hill Stone (Wissahickon Schist), pointed in a **Beveled Ridge jointMortar Mix: 1 part Ecologic™ Mortar G #DGM 250 (greenish ochre-brown colored) 1 ounce of mica fleck inclusions added to simulate the Pennsylvania’s Schuylkill River sand which has naturally occurring shist fleck inclusions.

Finish Tools – 1/2″ slicker, Churn brush

Note to those in Mt. Airy Region of Philadelphia- The above mix, or substituting DGM 200, is a good match for most Wissahickon Schist repointing work needed on buildings built before 1940.

Overhung Ridge Joint

The Overhung Ridge joint is often misinterpreted as one of the ribbon joints mentioned above. Overhung Ridge is a joint that meets the flush face of the semi-squared block of stone above it, having a trailing edge to the stone above it and a ruled edge with a inward bevel meeting to the stone below it. Usually the left side of the head joint has the trailing edge and the right side of the head joint, the ruled edge with bevel.

Ecologic™ Mortar G #DGM 250 (greenish ochre-brown colored)

Tools – 1/2″ ribbon jointer, loop and a level

Note that often in Overhung Ridge pointing of snecked rubble stonework, the head joints can be perfectly perpendicular with the horizontally level bed joints or the head joints are angled from the level bedding plane. From a distance this joint appears to make the semi-squared stones seem more squarely shaped. It also makes the joints look a lot like a ribbon joint, which they are not. Although no painted lime lines or additionally material is added on the surface of the ruled lines, the tightly compressed flat area of the Overhung Ridge joint typically dries lighter than the trailing and ruled edge which is scraped away to bleed into the surrounding texture of stone. This gives the appearance of a painted ribbon joint, but is not to say that in some instances pencylling was not still carried out. In Chestnut Hill, Philadelphia many original Overhung Ridge pointed buildings throughout Germantown Avenue and all the surrounding side streets can still be viewed.
The grapevine joint in stonework is a protruded bead. Easton, PA

Note to those in College Hill and the Easton, PA area: 1 part Ecologic™ Mortar G #DGM 200 (brown/grayish color) and 2lbs fine or medium grade slag flecks, (depending on the original mortar), is a good match for most mortar repointing work required on buildings built in this region before 1940.