Atelier saint André

Formerly, production of lime was guided by formulas known and passed down from generation to generation. Industrial lime production is now well-established at various locations. Recently an artisanal production, heiress of ancestral knowledge, began to answer the immediate needs of the population of European countries.

Digging In the Pyrenees, the raw material, the calcareous rock, was abundant. The lime kiln was dug on a sloping ground in order to avoid building a wall around the kiln.
The kiln The kiln itself was divided into two parts: the hearth and the high part determited by a projection on which to set the vault of the stones to be calcined.

Once the earthwork finished, a layer of clay was spread out over the walls of the kiln to help retain heat.

The limestones The artisans collected limestones and started to load the kiln.
Garnishing The garnishing was a delicate work and even dangerous for the workers. It was a matter of placing the stones to be burnt in balance, without any binder, in order to build a vault above the hearth.
The vault When the vault was completed, the artisans filled the kiln entirely so that the flame could pass through the stone layers in a homogeneous way.
An opening was dug downwards to feed the kiln with combustible materials. Cross section of the kiln
Filling the kiln After the kiln was filled, stones were mounded in a bulge above the surface of the ground to keep the heat in during the burning.
Burning The kiln was supplied by dry wood faggots having a strong calorific value, composed of thorny bush or boxwood.

The burning went on three days and three nights during which the workers took turns keeping the temperature of the kiln at a constant 1000 degrees.

Burning 2 While burning, the calcareous stone or calcium carbonate (CaCO3) is transformed into quicklime or calcium oxide (CaO) by losing its carbon dioxide:

CaCO3 - CO2 = CaO

Burnt stones The burnt stones were hand-picked and kept in containers safe from the air to prevent carbonation (which would remove the binding property from the lime).
Extinguishing Then the quicklime was "extinguished" by soaking it in half of its weight in water.
Desintegration 1
Desintegration 2
This hydration causes the quick disintegration of the stones and produces a strong release of heat.

Lime powder The achieve powder is called slaked lime or calcium hydroxide Ca(OH)2 according to the process :

CaO + H2O = Ca(OH)2

Lime was preserved in a dry place and locked up in containers or in hermetic bags. This process supplied a village with sufficient amounts for its everyday needs.

Photographs drawn from the documentary series : :
"Petits métiers des Pyrénées espagnoles", Pyrene PV, translation Imagine, Planète.

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Last update : Fri, Jan 9, 2009, P. Grall © ASA 2000 - 2009 All rights reserved.