CORICAL is a lime paint, based on fat hydrated lime, mineral additives and natural pigments.  Chemically, fat hydrated lime contains more than 92% calcium hydroxide ‘Ca(OH)₂’.  CORICAL is produced of extremely pure limestone.  This lime consists mainly of the mineral calcite ‘CaCO₃’.  When limestone is heated to a temperature of ~900°C, CaCO₃ will transform into calcium oxide (CaO), also named burnt lime or quicklime.  During this process, carbon dioxide (CO₂) will escape.  The chemical reaction is written as follows :

To the calcium oxide water is added, a process know as slaking.  The quicklime will transform into calcium hydrate :

Calcium hydrate is also known as slaked lime, referring to the slaking process.  The slaking is a very violent exothermic reaction, in which a great amount of heat is produced.  It is obvious that prudence is in order for the slaking action. 

Adding the exact quantity of water to fulfil the reaction, the hydrate is produced as a white powder.  By slaking with an excess of water, or by mixing the dry hydrate with water, a liquid substance is produced, namely a lime paint. 

Lime paints will harden by the reaction with carbon dioxide in the air.  This process is called carbonation.  The lime cycle is closed, as the hardened product has the same chemical formula as the original natural stone : calcite. 

The strength of a pure lime will also increase by drying the product, and the loss of water.  Often, an increase in strength is related with an increased brittleness.  Nevertheless, lime paint is a very elastic material due to its structure and high porosity, with a very high vapour diffusion capacity.  These characteristics are in glaring contrast with the properties of most of the synthetic paints.  .

Lime paint is a very alkaline product with an acidity of 12.5.  By carbonation the pH will drop to about 8.  Due to this high pH-values, lime paints have anti-fungal, bactericidal and disinfecting properties.  Another characteristic of an alkaline material is the neutralisation (to a certain extent) of acid rain. 

Nowadays, the environment is indeed a ‘hot topic’.  Looking carefully to the chemical reactions, one will observe that a same amount of CO₂ will be taken up during the carbonation, as was released during the burning of the limestone.  The result is 0! 

By colouring the lime paint in the mass, the natural pigments will be built-in in the calcite crystal lattice during hardening.  As a result, the pigments will not be able to migrate in the hardened product and consequently the lime paint will be colourfast. 

Arte Constructo bvba - Molenberglei 18 - B- 2627 Schelle (Belgium)

tel: +32 (0)3 880.73.73   fax: +32 (0)3 880.73.70

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