Lime
Thanks to these two videos, you will be able to meet Mr Daniel Pinel from the company Calci Chaux, our supplier of lime, who will explain the different stages in the manufacture of lime paste (slaked air lime in paste) and show you the quarry and the hundred-year-old kilns used for its manufacture. Calci Chaux is one of the last companies in France to produce handmade lime without additives for the building and agricultural industries.
Lime
Thanks to these two videos, you will be able to meet Mr Daniel Pinel from the company Calci Chaux, our supplier of lime, who will explain the different stages in the manufacture of lime paste (slaked air lime in paste) and show you the quarry and the hundred-year-old kilns used for its manufacture. Calci Chaux is one of the last companies in France to produce handmade lime without additives for the building and agricultural industries.
manufacture of lime
Slaked lime paste is obtained by hydration of quicklime from very pure limestone. The name recommended by the NFP 15311 standard is CL (Calcic Lime) followed by a number 70, 80 or 90 indicating the proportion of calcium carbonate (CaCO3). The higher the content, the fatter the lime. Air lime has been used since antiquity to make mortars for construction, plasters and whitewashes on walls. Calcination: The calcination of limestone at around 900°C (CaCO3) produces quicklime (Calcium Oxide: CaO) and a strong release of carbon dioxide (CO2): The reaction is accompanied by a weight loss of about 45%, corresponding to the loss of carbon dioxide.
Slaking: The transformation of quicklime into slaked lime is carried out by adding water (H2O). This slaking operation produces calcium hydroxide Ca(OH)2, with a strong release of heat. After transformation, the volume increase is about 30%. Slaking can be carried out in different ways: superficial sprinkling of the quicklime blocks, then termination of the reaction in air; immersion of the quicklime blocks in a large volume of water then termination of the reaction in air; mixing of water and lime in a mixer with control of the exothermic reaction (in industry); immersion of the quicklime blocks in a large volume of water then termination of the reaction in water.
In the first three cases, a powdered air lime is obtained (lime flower, fat lime, CAEB, slaked lime, etc.).
In the last case, the slaked lime produced takes on the appearance of a paste (slaked lime) which can be kept as long as water is kept on the surface to limit the exchange of carbon dioxide (and therefore carbonation). Powdered lime corresponds well to current building practices (volume dosing, mixing with a concrete mixer, etc.). Lime paste allows obtaining "fatter" mortars, less subject to rapid drying, renderings or whitewashes that carbonate less quickly and are therefore more resistant. On the other hand, dosing is more difficult, mixing with sand more delicate, unless the appropriate tools are used (planetary mixer, planer...).The better carbonation of lime paste is probably due to the fact that slaking takes place in the absence of air, so no partial carbonation occurs before setting.
Carbonation: The setting of air lime takes place by carbonation, i.e. by absorbing carbon dioxide (CO2) from the atmosphere: hence the name "air lime": Depending on the humidity of the environment, this reaction takes place over several months: water vapour binds with atmospheric carbon dioxide to form carbonic acid; the lime binds the carbon dioxide contained in this acid and is transformed into limestone. The result of this operation is limestone (CaCO3) again. The setting mechanism by carbonation takes place in the presence of water, hence the need to control the conditions of implementation (humidification of the supports, control of climatic conditions, etc.).