Might your point be that at degrees above 580 F the flax elements in the mortar would begin to carbonize and then provide no reinforcement? Maybe so but only the burning chamber of this oven was subject to such temperature - and even more - and this was made up of fire fast free standing precast elements. After some years of use I decided to reconfigure the encasing and in dismantling it noticed no change in the blocks or mortar other than some soot accumulation here and there inside the channeling. I smashed the excess clay blocks, mortar and plaster all up and reused it in putting the oven/heater back together.

Last edited by Cecile en Don Wa; 02/05/12 07:04 PM.