Lime is a versatile natural mineral resource and the collective name for a number of minerals (salts) of calcium, such as quicklime, slaked lime, chalk, marl and gypsum. It is derived from stone lime or shell lime which are fired in lime kilns at about 900°C. Lime is mainly used as a binding agent in plasters and mortar, but also as a soil improver or hardener.
Lime has proven to be one of the oldest and most durable building materials. From the first Stone Age settlements, the pyramids of Egypt, the famous frescoes of Pompeii and the Pantheon in Rome to the Sistine Chapel, lime is the basic raw material for important historical buildings or elements.
Production Process of Natural Hydraulic Lime
As a building material, lime undergoes a number of different manifestations from extraction to final product. We can speak of a cycle: from extraction of the lime to a final mortar or plaster and finally return to its original chemical form, calcium carbonate.
In nature, lime occurs in calcareous rocks such as marl, limestone and dolomite. These sediments are mined in specially constructed quarries. The shells or limestone (calcium carbonate - CaCO3) are burned in special lime kilns at temperatures around 900°C. In the process, carbon dioxide (CO2) is excreted and calcium oxide (CaO) is formed. The calcined lime is called the living or quicklime.
The burnt lime or live lime is then brought into contact with water, this is called quenching. This produces a chemical reaction that releases a lot of heat, called an exothermic reaction. The combination of quicklime (CaO) and water (H20) produces calcium hydroxide (Ca(OH)2).
Natural Hydraulic Lime hardens through contact with water and by absorbing carbon dioxide from the air. This process is called carbonation. Proper hardening or carbonation must be done slowly - the slower the hardening, the better the end result.
See in detail the production process of Saint-Astier lime here.
The benefits of lime (in construction, renovation and restoration)
The great advantage of lime is that it is very flexible. Although lime hardens, its elasticity means it never really becomes "solid. Compared to cement, lime is strong but less hard, which makes it ideal for old substrates.
Lime, through its alkalinity, contributes to a better living environment. Due to its high pH, all kinds of microorganisms do not stand a chance. Fungi and biocides are unnecessary in lime-based mortar. Lime plasters are less affected by water and do not soften. They also do not dissolve or rot. With gypsum plaster, for example, this can happen.
The use of lime in mortars and plasters brings numerous advantages. In a lime mortar, hydraulic lime is the binder with possibly a small addition of cement. This composition gives the mortar a higher compressive strength and some flexibility. This prevents tension differences between the restored and existing masonry. The lime also provides the self-healing effect to the plaster. The plaster remains elastic and can absorb deformations without cracking. The free lime can crystallize in the pores and reduces the risk of salt efflorescence. Be sure to read our article "Why choose a lime plaster?" to learn all about the benefits of lime plasters.
In addition to use in plasters and mortars, natural hydraulic lime also offers numerous benefits for chapes. Be sure to read the LinkedIn article in English to learn more.
Different types of lime
1. Air lime
Air lime is a "soft" lime that hardens only by carbonization or exposure to air. The main advantage of air lime is its microstructure. Plasters based on air lime are less pressure-resistant but offer a number of constructional advantages such as good workability, stability and good adhesion to the substrate. It is still often used in restorations.
Among others, Saint-Astier's Décorchaux(CL 90 - S) is an air lime that can be used as a plaster, as is our RC Calcoliss 300.
2. Traskalk
Trash lime is a binder for making mortars and plasters. It is nothing more than lime mixed with tras, a pozzolanic rock found only in Germany. Trash lime is suitable for a lot of applications. The most important are its use in cement and plaster, both indoors and outdoors. The material adheres well, is solid and is water resistant. For these reasons, lime is mainly used for plastering exterior walls.
3. Hydraulic lime (HL).
Hydraulic lime is a collective term. This is lime or slaked lime used to make lime plasters that harden under the influence of water. By using hydraulic lime as a binding agent, lime plaster is water-resistant, water-vapor permeable, moisture regulating and mold resistant. This thus has a positive effect on moisture management.
Among others, Saint-Astier's Chaux Colorée is a plaster based on hydraulic lime.
4. Natural hydraulic lime (NHL).
Natural Hydraulic Lime or NHL (Natural Hydraulic Lime) is a type of lime that contains impurities such as loam and is created by heating or calcining limestone. The lime reacts with the clay particles in the lime kiln to form silicates that harden partly by hydration. The particles that do not convert by bonding with clay particles are quenched, so to speak, into calcium hydroxide that then hardens again by carbonization or air. Natural hydraulic lime is characterized by a combination of carbonating and hydraulic properties.
Decoding the type of NHL lime is determined by its compressive strength. When is it best to choose which type? Which type do you choose for your application? For "hard" applications, choose the most pressure-resistant type: NHL 5. For "soft" applications, opt for the NHL 2. If you don't need NHL 2 or NHL 5, choose NHL 3.5.
- NHL 2
NHL 2 is suitable for use on soft, permeable masonry with minimal exposure. It is softer and slow curing. This product is suitable for indoor use, or applications where preservation of soft or deteriorating (brick) masonry is a primary requirement.
The Téréchaux of Saint-Astier is an NHL 2.
- NHL 3.5
NHL 3.5 is the lime binder for most exterior applications. The lime binder takes only a few days to take on its final form, making it ideal for medium-density masonry with moderate exposure and for moderately permeable masonry materials.
Saint-Astier's Chaux Blanche LC**** is an NHL 3.5. In addition, our balay mortar RC Kalei, lime paint RC Calco, grout RC Astivo and restoration mortar RC Amostone / St.One are based on NHL 3.5 from Saint-Astier.
- NHL 5
NHL 5 is the lime binder where greater hardness and compression strength is required. We are talking about impervious masonry with heavy loads, chimneys, and anything around or below floor level. Of all NHL binders, this one is the most resistant to frost and has the highest resistance to crystallization of salts. Furthermore, this binder provides the highest wear resistance and surface hardness of the mortar/plaster.
Saint-Astier's Chaux PureTradi 100 is an NHL 5.
The unique lime of Saint-Astier
Founded in 1912, the family-owned company Saint-Astier is to this day the largest independent French producer of lime. The unique composition of Saint-Astier limestone makes it possible to produce - without mixing or selection - a natural lime. This lime has the ability to harden under water as well as recarbonate in contact with air. Saint-Astier lime has a very constant concentration of silicon, a low concentration of aluminates, sodium and alkaline and a high concentration of aliten. This composition provides very stable and hydraulic properties.
These hydraulic and aerial properties make it a lime with exceptional mineralogical properties, unchanged since the first extraction of the quarry, and unique in Europe. With a team of 140 men and women, Saint-Astier produces and distributes hydraulic natural lime, formulated lime and technical mortars for heritage restoration, renovation, new construction and eco-housing.
Reynchemie: expert in lime
Since the start of Reynchemie in 1988, we developed an expertise in all kinds of lime products. In 2003, we became the exclusive distributor of Saint-Astier lime products in the Benelux. In addition to the standard Saint-Astier lime products, we also have our own lime-based products such as lime-based caulking(RC Kalei), lime filler based on air lime(RC Calcoliss 300), colored jointing lime(RC Astivo), lime paint(RC Calco), salt-buffering mortar(RC Sanisel) and, more recently, 2 high-quality lime plasters: RC Intralime G & RC Intralime F.
Our technical-commercial consultants are always at your service in case of technical questions and quotations. View contact details here.
