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:
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.
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.
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.
Some indication of vapor exchange (permeability) in mortars are:
Figures are expressed in grams of air x m2 x hour x mmHg.
The EU norm (soundness test in accordance to EN 459-2/220.127.116.11) 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.
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.
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.
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.
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.
9. Resistance to sea salt and road spreading salt effects
Check 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.
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.