Saturday, April 21, 2012

Hot Rocks - Cool Putty

At the lime kiln demonstration this week in North Carolina, extreme heat was added to Ca Co3 (limestone) which drove off the carbon dioxide (which has a substantial weight) and turned it into CaO (quicklime)


Here quicklime is cooling in the lime kiln flue stack after the 'burn' the morning after. The students, under the direction of Steve Cohan, had made the kiln previously and burned the limestone in it all night long .


The material is removed from the kiln ad put into buckets


When you add water H2O to quicklime it makes Calcium Hydroxide Ca (OH)2 or lime putty. This is called 'slaking'. The quicklime is in a very volatile state. The water heats up and creates lots of bubbles and smoke The unburned limestone is then filtered out through an expanded 3/8 lath and the remaining filtred lime is mixed into a creamy lime putty


When you add an aggregate, like sand to the putty and let it 'set up', the water leaves and carbon dioxide is absorbed from the atmosphere and it becomes once again Ca Co 3. The lime mortar gets heavier and heavier over time.


In this case it is used for 'rendering' the brickwork

Basically the process amounts to turning rocks into 'liquid stone' for the purpose of using it in semi-liquid form to coat the surface of the bricks or stonework leaving it to harden and become stone again.

Is this method of turning rocks into liquid stone the opposite of doing dry stone work?   I wonder.



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