Tuesday, January 31, 2012

Brick Oven Curing

In the process of building a brick oven a number (3-8) of gallons of water are used to mix mortar, insulating layers, and outer shells of stucco etc.
This water will evaporate very slowly on its own.
Curing the mortar requires that we leave it moist for at least a couple of weeks. Following that a warming fire is lit in the oven and the bricks are heated gradually.  When the radiant heat reaches the moisture in the masonry it drives it outward. This is where you want to give it somewhere to go. If tightly enclosed, an oven at this stage will weep water that has condensed on cool outer surfaces making it seem as if there's a sprinkler running above the dome.
evidence of a good draft in the throat
So start small and go slow. Then close up the oven mouth and let the heat radiate. Do this a couple of times, increasing the fire  until the oven is 'up to temperature'. This can be measured visually (carbon burns off the roof of the dome at about 600 degrees) or with probes or infrared thermometers.
It may take a few real firings to get all the moisture out and you may smell the steam from the heating but eventually you'll have a thoroughly dry masonry unit.

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