Thursday, April 19, 2012

You put the limestone in the ...

The hand of Steve Cohan.

Steve Cohan of Hot Rock Masonry is having his MSA students build a small traditional wood burning lime kiln. 

He designed it on a very good drawing program called Google Sketchup

At the demonstration build Steve checks the details of his design regularly on his laptop.

Progress goes well throughout the day. The kiln is built with fire bricks and clay. It is designed to do one burn of limestone which is stacked in the main brick chamber as it is built and then is heated to about 800 degrees F.  from two lower chambers feeding into the centre. They will make quick lime from the limestone and then slake it to make hot mud and plaster which are the traditional materials of masonry for the last two thousand years.  

Here Steve is placing the pieces of limestone (which is essentially chunks of calcium carbonate) carefully in the kiln, so that the intense heat from the furnace can shoot up and around the rocks and produce a complete chemical reaction. This fitting of the stones so that there is space between them seems like the inverse of what we do when we are dry stone walling. The limestone has to be stacked with the least amount of contact between each of the rocks.


  1. John,
    Say hello to Steve Cohan for me. We worked on at least one other lime kiln together and have worked on dry stone walls etc. I visited him on Orca Island where he has his own personal limekiln and has also repaired a large historic kiln close by. Steve builds masonry heaters for a living and has a great knowledge and interest in lime kilns.

  2. I imagine, there would need to be sufficient air spaces between the limestone pieces in order to generate a hot enough heat for a chemical reaction to take place. Quick lime (although not a quick process) was also used on crop fields as it would neutralize the Ph balance for crop growing fields as it added calcium and magnesium that help lower the acidity level.
    Is it the calcium carbonate that chemically reacts to the water making it boil?