The information given by lime manufacturers to allow the specifier to have a clear definition of the chemical structure, mechanical properties and performance of their products is essential. The lack of this information has led not only to confusion but also to misuse and, regrettably, to problems which have been wrongly attributed to the lime and the mortar produced.

What you should know and how to check that you have the correct product.
(and relevant St. Astier information).

There are a number of products on the Market which can interest the specifier, however it is important to know what to choose. St. Astier Natural Hydraulic Limes are chosen for a number of reasons, the most important of which are:

Absence of or only traces of soluble salts such as SO3, K2O (Potassium Oxide)
and Na2O
(sodium oxide), tri-calcium aluminate (C3A). No gypsum additions.

This is to avoid sulphate attack which normally happens in mortars prepared with cement or
where white cement has been introduced into so called natural hydraulic lime at manufacturing
point to ensure an hydraulic setting. When cement is present, you will find a high percentage of
C3A which will react with the sulphates producing an overall expansion and the eventual
disintegration of the mortar joints.
Another addition made at manufacturing source could be Gypsum. Products containing Gypsum
addition should be avoided as Gypsum is high on sulphates.
Presence of K2O and Na2O (Alkali), even in apparently small quantity (approx 1.5% in ordinary
cement) could react with the silica in the aggregate causing an alkali-silica attack with similar
consequences as suplhate attack.

How to check: ask your supplier to provide a chemical /mineralogical analysis certificate or
conduct a laboratory check on a random sample.

St. Astier information: no cement or gypsum addition, only insignificant
traces of potentially damaging components are found in St. Astier NHL's
EU norm EN 459.1
Max. SO3 limit-% 3-7
St. Astier NHL 5/3.5/2
SO3 content/average-% 0.31 - 0.45
% 0.40 - 0.70
% 0.12 - 0.21
% 0.04 - 0.07
% 0.50 - 0.70

High % of available lime (after slaking).

Available lime (free lime) is important for workability, self healing properties and elasticity. It will also contribute to final strength.
Free lime will allow some tolerance for initial structural movements. NHL mortars will therefore offer adequate strength with enough plasticity to accept slight load shifts.

St. Astier information
Available lime to comply with NHL (natural hydr. lime) definition in EU and French norms

EU 459.1 norm

French NFP 15.311
St. Astier NHL

What you should look for in a pure NHL product: a high % of free lime.
How to check: ask your supplier for the relevant information or conduct tests.
Good vapor exchange qualities
Essential to ensure breathing and therefore absence of condensation and dampness.
Some indication of vapor exchange (permeability) in mortars are:

Concrete 0.15Cementitious mixes (1:1:6) 0.23 - (1:2:9) 0.25
Hydrated lime mortars 0.46/0.51Putty lime mortars (22%)          0.57

St. Astier NHL Mortars: 0.55 - 0.72
(made with well graded #6 to #200 sands to ensure good void structure)

St. Astier NHL EcoMortar 0.80

Figures are expressed in grams of air x m2 x hour x mmHg.

Low expansion (soundness test) and quick lime residual (CaO).

The EU norm (soundness test in accordance to EN 459-2/ specifies a value of <2 mm.
All St. Astier production is checked continuously for soundness and materials with unacceptable values are rejected (not recycled).

The presence of quick lime would make an unstable mortar.

Make sure that your supplier gives you these values to avoid problems.

St. Astier information
Expansion values of NHL products

All St. Astier NHL products have an expansion value of < 1mm
Quick lime presence: < 1%

Quick setting (resistance to frost, rain and wind)

Pure and natural hydraulic lime mortars do not need to be protected for a long time. Manufactures should however give indications on the minimum time required. The quick resistance to bad weather conditions is an additional assurance also in changing seasons when a sudden change of weather could damage work which was left unprotected. Fresh mortars, however, should not be allowed to get saturated by rainwater as they might be susceptible to frost damage, especially in the finishing coat. Depending on the region, this might be the case in work completed as early as October.

St. Astier information
NHL products - Minimum frost and bad weather protection time on dry mortars
 NHL 5   48h NHL 3.5   72h NHL 2   96h 

Query on pozzolanic or other additions

Products that requires these additions are not offering a constant and reliable performance or need a "push" according to the season. Most of the times no data are available on the effect of the additions over a period of time. Furthermore additions will add to cost and to possible mistakes on site dosages. The various degree of hydraulicity offered by the St. Astier range make additions obsolete.

7. Low density

It comes into consideration when material costs are examined. In volumetric mixes the higher the density of the binder the higher will be the amount you would have to use in weight.

CHECK: bulk density of the proposed binder.

St. Astier information
Binder consumption for 1cu.ft of mortar.
    VOLUME OF MIXES / lbs/cu.ft (+/-10%)
Average Density (+/-10%)
NHL 3.5
Lime Putty



8. Whiteness index

The whiter the product the better results will be obtained in reproducing the color of the aggregate used. The St. Astier range offer some of the whitest NHL product on the Market.

St Astier information - Whiteness index "Y"
Barium sulphate (pure white) Y = 100
NHL 5 =Y 67    NHL 3.5 = Y 72    NHL 2 = Y 76

  9. Resistance to sea salt and road spreading salt effects

that the lime you intend to specify will not be affected by these agents when designing a mortar to be applied in areas subject to these influences. Lime containing cement or gypsum would not be suitable. St. Astier NHL products have been successfully used in these conditions without deterioration.


It is essential that the right aggregate is used in making hydraulic lime mortars. Monogranular or very fine sands could have disastrous effects and should be avoided or used as a minor proportion of the mix (max 20%). Sands suitable for NHL mortars must be well graded from #6 to #200.
Finer sands, still well graded, can be used, In the case that the fine portion contains silt or clay the binder amount will be reduced. Remember that clays and silt will retain water increasing the drying period and therefore the risk of frost damage.

Notes regarding St. Astier NHL products.

Products range.
St. Astier produces NHL 5 (eminently hydraulic), NHL 3.5 (moderately hydraulic) and NHL 2 (feebly hydraulic). It is a unique range at the disposal of the specifier as it will provide the correct binder for most uses without recurring to blending. The range is completed by the availability of hydraulic lime paints and ready mix mortars. These are also supplied pre colored.

Packing and shelf life. All products are packed in heavy duty bags with intermediate plastic membrane. All bags are batch numbered with date and time of production. The shelf life of NHL products is approx. 12 months if stored in dry and ventilated conditions. Pre colored products should not be used after 6 months.

Raw material. Consisting only of limestone infiltrates by silica. Only traces of other elements are present. This assures constant uniformity of the final product. The exploitation area extends for about 75 acres with permitted excavation between 25 and 40 feet. deep.

Manufacturing process. Totally automated production with capacity of up to 100.000 tons per year. Controlled burning (max. 1850o F) using the purest anthracite coal from Wales to avoid high sulphate contamination and color alteration. CO2 tests are continuously performed after burning to regulate slaking. Soundness tests reject substandard materials (over 2mm expansion).

Experience. Established since 1851, St. Astier is supplying reliable products for all building requirements. The St. Astier Technical and Research Dept. conducts strict and continuous quality control on all products. These include tests on compressive and tensile strength, elasticity, adhesion, workability, setting etc.... In UK the St. Astier products are stocked and distributed only through a network of specialist Companies, able to assist, if required, in mortar design and application recommendations.