Lime building material

Lime used in EcoConstruction

Key words: construction, mortar, wall, cement, eco-construction, moisture, benefits.

Why use lime in EcoConstruction?

Lime has the following advantages over conventional cements.

  • Permeability
  • Lime absorbs little moisture and rejects it quickly: it is a “breathable” material. The main defect of walls mounted with cement is the rise of soil moisture by capillary action. As the cement is waterproof, this moisture cannot evaporate and remains in the walls, causing corrosion and cracking of materials, mold, etc. Lime, on the contrary, rids the walls of their moisture and therefore eliminates the associated problems.

  • Plasticity
  • All walls “work”: they naturally collapse over time, react to variations in the terrain and other factors. The plasticity of lime allows it to accompany these movements while keeping the cohesion of the structure, unlike cement which, due to its rigidity, will tend to break, thus creating cracks and compromising the strength of the structure. together.

  • Its disinfecting properties
  • Think of "liming" stables: lime limits the proliferation of mites, fungi, saltpetre and bad smells. It helps to clean up your environment in a natural way.

  • Versatility
  • In construction, the uses of lime are multiple and above all, it is suitable for almost all types of media, whether straw, stone, terracotta, mud or other.

  • Aesthetics
  • The feeling of softness and well-being that emanates from a lime wall is not to be neglected. On the other hand, if the lime is mixed with local sands, it allows a harmonious integration into the soil and gives an inimitable character to your construction.

The principle of obtaining lime

Lime is obtained by firing limestone at around 900 ° C. This calcination evacuates the carbon dioxide contained in the limestone and produces what is called "quicklime". Quicklime is extremely water-hungry and “burns” any organic body that comes in contact with it by emptying it of the water it contains. The next step is therefore to “extinguish” the quicklime by adding water to it. If the amount of water added is limited, the lime will take the form of a very fine powder and if the amount of water is excessive, it will have the consistency of a more or less thick paste.

After processing, the carbonation process begins. To go quickly, the humidity of the mortar makes it possible to capture the carbon dioxide present in the air and thus lime will gradually find the carbon dioxide which had been removed from it during calcination and return to its state. of limestone. This process can take months.

Aerial lime and hydraulic lime

For the lime cycle described above to be perfect, very pure limestone is needed. In this process, the carbon dioxide that allows carbonation comes from the ambient air. This is why lime obtained from pure limestone (or almost) is called "aerial lime".

However, pure limestone is relatively rare. It generally contains other elements, in particular silica. But this impurity is not a constraint, quite the contrary, since it gives other interesting properties to lime.

Silica combines with limestone during calcination and gives more resistance to the mortar. The more silica there is, the harder and more resistant the coating will be, but it will also be more brittle. On the other hand, carbonation will no longer only take place from air, but also in the presence of water: this is why some of these lime can be used under water. These are hydraulic limes.

Learn more about lime:
- Forum HQE and eco-construction
- User manual for natural hydraulic lime in EcoConstruction by Olivier Labesse (.pdf of 54 pages and 1.3 MB members only)

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