Gebluste kalk en hydraulische kalk
Wat is gebluste kalk? Het is een van de hoofdbestanddelen van marmerstuc en betonmarmer. STUCAMOR marmerstuc en betonmarmer worden gemaakt met de gebluste kalk van onze leverancier Bericalce. Zij hebben authentieke kalkovens waar de kalk op historische gebrand en geblust wordt.
Hieronder de uitleg die Bericalce geeft over gebluste kalk
Types of Lime
Lime Hydrate (Superfine Lime)
Obtained by using a quantity of water almost equal to the quantity of lime.
The hydrate is a soft powder and finely separated. Sold in paper bags, like cement, and it must be kept in a well dry place. It’s less sensible to frost than grassello.
Lime Grassello. Obtained by using a quantity of water higher than the quantity of lime (approximate ratio 3:1). The Grassello becomes a plastic mass and oily at touch. In the past, rarely also today, the lime was slaked in holes in the ground where it was put under water for months (aging). It’s important to know that an insufficient slaking of limestone lumps, causes serious problems for mortar. The lumps slake later after use, increasing their volume and therefore creating swells and crumbles. Nowadays, grassello is sold packed in plastic bags, ready to use.
Setting and hardening of Lime
The main characteristic of lime is to compose a product that, when mixed with charges, results easy to work and mold until damp. Once dry, the product is quite water-resistant and has good mechanic properties as well as stability in time.
This characteristic is based on a chemical reaction of slaked lime and carbon dioxide :
While the mixture is drying, the water evaporates and forms carbonate of lime.
This is called CARBONATION: lime returns to the identical composition of the limestone but with very smaller crystals than in origin. The reaction of carbonation is very slow due to the low concentration of carbon dioxide in the air therefore the complete transformation of lime hydrate in carbonate needs even years. This is called “air” lime since it’s necessary the contact with air for setting. The evaporation of water causes a shrinkage of volume.
For this reason slaked lime is never used alone but always with an inert charge to avoid breaking.
Onderstaand artikel geeft nog meer uitleg over deze oeroude bouwstoffen.