Lime is a versatile natural mineral raw material and the collective name for a number of minerals (salts) of calcium, such as quicklime, slaked lime, chalk, marl and gypsum. It comes from rock lime or shell lime that is roasted in lime kilns at approximately 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 sustainable 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 historic buildings or elements.
Production process of Natural Hydraulic Lime
As a building material, lime undergoes a number of different forms from extraction to final product. We can talk about a cycle: from the extraction of lime to a final mortar or plaster and finally returning to its original chemical form, calcium carbonate.
In nature, lime occurs in calcareous stones such as marl, limestone and dolomite. These sediments are extracted in specially constructed quarries. The shells or limestone (calcium carbonate - CaCO3) are roasted in special lime kilns at temperatures around 900°C, separating carbon dioxide (CO2) and forming calcium oxide (CaO). The burnt lime is called live or quicklime.
The burnt lime or living lime is then brought into contact with water, which is what we call extinguishing. This results in a chemical reaction that releases a lot of heat, a so-called exothermic reaction. The combination of quicklime (CaO) and water (H20) produces calcium hydroxide (Ca (OH) 2).
Natural Hydraulic Lime hardens by contact with water and by absorbing carbon dioxide from the air. This process is called carbonation. Good hardening or carbonation must be done slowly — the slower the hardening, the better the end result.
View in detail the production process of Saint-Astier lime here.
The benefits of lime (in construction, renovation and restoration)
The big advantage of lime is that it is very flexible. Although lime hardens, it never really becomes “solid” due to its elasticity. Compared to cement, lime is strong but less hard, making it ideal for old surfaces.
Due to its alkalinity, lime contributes to a better living environment. Due to the high pH value, all kinds of microorganisms have no chance. Fungi and biocides are superfluous in calcareous mortar. Lime plasters are less affected by water and do not soften. They also don't dissolve and don't rot. With gypsum plaster, for example, this can happen.
The use of lime in mortars and plasters has many advantages. In a lime mortar, hydraulic lime is the binding agent 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 brickwork. 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 being used in plasters and mortars, natural hydraulic lime also offers numerous benefits for chapes. Be sure to read the English LinkedIn article for more information.
Different types of lime
1. Air lime
Air lime is a 'soft' lime that only hardens by carbonization or exposure to air. The great advantage of air lime is its microstructure. Air-based plasters are less pressure-resistant but offer a number of building physical advantages such as good workability, stability and good adhesion to the surface. It is still often used in restorations.
Among other things, the Decorations (CL 90 — S) by Saint-Astier is an air lime that can be used as a plaster, just like our RC Calcoliss 300.
2. Traskalk
Traskalk is a binding agent for making mortars and plasters. It is nothing more than lime mixed with grass, a puzzolan rock that only occurs in Germany. Traskalk is suitable for many applications. The most important are the use in cement and plaster, both indoors and outdoors. The material adheres well, is sturdy and is water resistant. For these reasons, traskalk is mainly used for plastering exterior walls.
3. Hydraulic lime (HL)
Hydraulic lime is a collective name. This is lime or slaked lime that is 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-permeable, moisture-regulating and fungicidal. This thus has a positive effect on the moisture balance.
Among other things, the Chaux Colorée by Saint-Astier 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 clay and is created by heating or calcining limestone. In the lime kiln, the lime reacts with the clay particles and forms silicates that partly harden through hydration. The particles that do not convert by bonding with clay particles are, as it were, quenched into calcium hydroxide, which 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 the best time to choose which type? What type do you choose for your application? For “hard” applications, choose the most flameproof 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.
- ZERO 2
NHL 2 is suitable for use on soft, permeable masonry with minimal exposure. It is softer and slowly curing. This product is suitable for indoor use, or applications where preservation of soft or deteriorating (baking) bricks is a prerequisite.
The Terechaux van Saint-Astier is an NHL 2.
- NHL 3.5
NHL 3.5 is the lime binder for most outdoor applications. The lime binder only takes a few days to take its final shape and is therefore ideal for medium-density masonry with moderate exposure and for moderately permeable masonry materials.
The Chaux Blanche LC**** by Saint-Astier is an NHL 3.5. In addition, our clay mortar is RC Kalei, lime paint RC Calco, grout RC Astivo and restoration mortar R.C. Amostone /St.One based on NHL 3.5 by Saint-Astier.
- ZERO 5
NHL 5 is the lime binder where greater hardness and pressure are required. We're talking about impermeable masonry with heavy loads, chimneys, and anything around or below floor level. Of all NHL chalks, it is the most resistant to frost and has the highest resistance to the crystallization of salts. Furthermore, this binding agent provides the highest wear resistance and surface hardness of the mortar/plaster.
The Chaux PureTradi 100 van Saint-Astier is an NHL 5.
The unique limestone of Saint-Astier
The family business Saint-Astier was founded in 1912 and is the largest independent French producer of lime to date. The unique composition of the Saint-Astier limestone makes it possible - without mixing or selection - to produce a natural lime. This lime has the ability to harden underwater and to recarbonate in contact with air. Saint-Astier's lime has a very constant concentration of silicon, a low concentration of aluminates, sodium and alkaline and a high concentration of alites. This composition provides very stable and hydraulic properties.
These hydraulic and air-technical properties make it a lime with exceptional mineralogical properties, unchanged since the quarry's first reclamation, 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-homes.
Reynchemistry: expert in lime
Since the start of Reynchemie in 1988, we have developed expertise in all kinds of lime products. In 2003, we became the exclusive distributor of Saint-Astier's lime products in the Benelux. In addition to Saint-Astier's standard lime products, we also have our own lime-based products such as lime-based kalei (RC Kalei), lime filler based on air lime (RC Calcoliss 300), colored grout (RC Astivo), lime paint (RC Calco), remediating salt buffering mortar (RC Sanisel) and recently also 2 high-quality lime plasters: RC Intraline G & RC Intralism F.
Our technical and commercial advisors are always there for you in case of technical questions and quotes. View contact details here.
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