General Installation Guidelines
NHL Mortar preparation:Ā 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:Ā 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 5Ā 10.5 Gallons of clean water. Mix withĀ whisk. If casein is used water content can be reduced |
Gravity Feed | 1 Bag NHL 5 :Ā + 16.9 Gallons (2.4 ft Cubic ft approx ) fine sand. Add water to required consistency |
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Main Rules : Do not over saturate with water, mix well, use well graded sands.
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Re-Pointing Masonry Walls: Brick, Blocks and Natural Stone.Ā
Understanding mortars.
Before deciding to re-point a basic understanding of the function of mortars is required. Ā Mortar is used for jointing individual units in a mass of masonry.Ā The final structure must have certain characteristics to function satisfactorily.Ā 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.Ā 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 etcĀ ) 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.
Preparation:
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.
Application:
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 ĀfingerĀ thick, if the joints are wider than this they should be pinned with compatible matching masonry.
Finishing:
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 Āwell filledĀ 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
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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 |
Lime
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Sand
(sieve size) |
Ratio LimeĀ : Sand |
Ashlar / Tuck joint | 1/32″- 3/16″ | Ashlar / Tuck pointing mix or Ecologic F |
NHL 2
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#20 to #200 | 2 : 1 |
High porosity masonry | 3/16″-3/8″ | Ecologicā¢ G |
NHL 2
NHL 3.5 |
#18-10 to #200 | 1 : 2Ā 1 : 2.5 |
3/8″-3/4″ | Ecologicā¢ G |
NHL 2
NHL 3.5 |
#6-3 to #200 | 1 : 2 1 : 2.5 |
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Medium porosity masonry | 3/16″-3/8″ | Ecologicā¢ G |
NHL 2Ā Ā
NHL 3.5 NHL 5 |
#18-10 to #200 | 1 : 2 1 : 2.5 1 : 2.5 or 3 |
3/8″-3/4″ | Ecologicā¢ G |
NHL 2
NHL 3.5 NHL 5 |
#6-3 to #200 | 1 : 2 1 : 2.5 1 : 2.5 or 3 |
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Low porosity masonry | 3/16″-3/4″ | Ecologicā¢ G |
NHL 3.5
NHL 5 |
#18-10 to #200 | 1 : 2.5 1 : 2.5 or 3 |
3/8″-3/4″ | Ecologicā¢ G |
NHL 3.5
NHL 5 |
#6-3 to #200 | 1 : 2 1 : 2.5or 3 |
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Interior Floor tiles or stone slabs | 1/32″-3/16″ | Ecologicā¢ F |
NHL 3.5
NHL 5 |
#18-10 to #200 | 1 : 2 1 : 2 or 2.5 |
3/16″-3/8″ | Ecologicā¢ F or G |
NHL 5
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#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
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1:2 | |
1/4″-1/2″ | Ecologic LimeCrete-C Field-Mix |
NHL 5+ Special Cement Additive
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1:2 |
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 Ā in determining the correct choice of materials, methods of application and Ā 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 NHLĀ plastering mortars instead of non hydraulic putty mortars reduces the working time by about 50%.Ā NHL mortars offer similar vapor exchange qualities as putty mortars but are more robust, can be sprayed andĀ used for decorative plaster work without the addition of gypsum.Ā Requiring less after care than putty, it can be applied in 2 coats on good levelĀ backgrounds. Mortar: Background: Internal walls can be uneven and rough, often with areas that have been altered.Ā Different background conditions are therefore common and this needs to be addressed before plastering.Ā 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.Ā 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.Ā 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.Ā 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 ā 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.Ā 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.Ā 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 theĀ 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 theĀ Making NHL MortarsĀ data sheet.Ā 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.Ā The hair should be long and strong, free from lumps and clumps. Fiber reinforcement should be alkali resistant.Ā 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 ā 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 beĀ lightlyĀ 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.Ā 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 theĀ background. Second coat orĀ Floating coat |
Setting Stuff or Finishing coatĀ (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.Ā 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: Good working practices:
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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:
In rendering, sharp and well graded sands should be used for all coats. 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.
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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 1/2ā³ to 2 3/4ā³ 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 ā 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 |
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. GRAVITY FILL MORTAR.
Casein addition is possible (see above). General: The addition of casein will increase the compressive strength and the set whilst improving flow and reducing the water demand.Ā Shrinkage, already low in NHL products and mortars, will be further reduced due to the lowerĀ water content of the grout.
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Lime ConcreteĀ for Floors, exposed aggregate / tamped finish
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Lime Concrete for Fine / ruled finish floors
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Lime concrete sub base for slabs.
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Ā Jointing / Pointing mortar for slabs.
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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. *
Choice of materials Preparation Dubbing out: Suction control: |
Prewetting: 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 mortarās 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: 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: |
Second Coat (Undercoat/scratch coat) 2 : 5 / Lime (NHL2) : sharp sand The scratch coat should not be applied for at least 3 ā 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 ālay it up and leave it alone.ā Thickness not exceeding 5/8ā³. Keying is best achieved by providing a crisscross pattern of a 2ā³ 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 orĀ EcoMortarĀ (premixed) 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 ā 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:Ā 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 āGeneral Guidelines āĀ NHL Rendersā contains further notes on protection and good working practice.
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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:Ā 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:Ā 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 ā 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:Ā 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.Ā 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.Ā 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:Ā 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:Ā 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:Ā Made from pure high calcium hydrated lime. Acrylic addition: max. 5%. Pigments: mineral or earth oxides. Normal dilution ratio āĀ Ā 1 vol. powder: 2 vol. water (1kg. Powder: 4 litres water)
Shelf life:Ā 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:Ā Irritant to the eyes and skin. Wash affected areas abundantly with clean water (do not use soap).Ā 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
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NHL Renders
General information |
Other General Guidelines documents: Render on cob |
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:
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 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: Dubbing out: Suction control: It should be noted that in the presence of different suction levels the degree of dampening will vary accordingly. |
Keying: 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 workĀ 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: Finishing coat: Smooth and light textured finishes: Coarse finishes: |
First coat: 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): Ensuring a level surface: 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. |
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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 saturatedĀ 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 andĀ 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). FrostĀ 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. |
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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.Ā 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.Ā 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)
Application.
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 1ā³ 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.
Mixing.
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.
Consumption:
3281 linear feet of bed joints, at 3/32ā³ thick, and 4ā³ on bed requires 52 Gallons of mortar. Re-pointing 3281 linear
metres of 3/32ā³ thick joints at a depth of 3/8ā³: 5 Gallons of mortar are required.
Re-pointing:
SeeĀ Pointing with NHLĀ (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 |
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 1ā³. The pressure should not exceed 3.5 Bar*. Two coat work is normally sufficient with the use of a spray gun. |
Overall render thickness
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3/4ā³-1ā³ | 1ā³-1 3/8ā³ | up to 1 9/16ā³ | |
On surfaces with low keying | (for thickness above 1 9/16ā³ please consult us.) |
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Stipple coat NHL 5 or NHL 3.5 @ 1: 1.5 Sands: well graded 5mm down to 0.075 |
1/8ā³- 3/16ā³ | 1/8ā³-3/8ā³ | 3/16ā³-5/16ā³ |
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 |
3/8ā³- 5/8ā³ | 3/8ā³-5/8ā³ | 3/4ā³-1ā³ |
Leave for a minimum of 4 days depending on weather conditions, coat thickness and the plastererās judgment. Level using a straight edge and key with criss-cross pattern. If this is also the finishing coat (3/4ā³-1ā³), depending on the finish required, a finer sand can be used (#6 to #200 mesh). |
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2nd coat (finishing coat) | 3/16ā³-5/16ā³ | 3/16ā³- 3/8ā³ | 3/16ā³-3/8ā³ |
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 3/16ā³. |
Notes:Ā 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 |
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I need a PDF version of this pages information.
https://www.limeworks.us/resources/general-installation-guidelines/
Hi Nate! Thank you for reaching out. We do not have these available in a document form, however, if you let us know which guidelines you are interested in I can prepare a few for you. If so, please contact us at https://www.limeworks.us/contact-us/ with the pdfs you would like sent to you.