Date: Thu, 5 May 2009
From: "Vin Jannetty"
To: "Jim Buckley"
I built my first oven over 10 years ago when I lived in Texas. We talked on the phone back than and you were very helpful and the oven came out great. I moved to Pittsburgh, and my wife wanted a stone exterior finish to my latest oven, so I hired a mason to install it. I gave him your instructions and he followed them very closely. The oven was built in the winter and I cured it on one of the warmer days in the winter. For some reason the top of the oven cracked and propagated along the base as well. The cracks are large enough that I am loosing more heat than I want.
My question is do you think that I can fill in the cracks with refractory mortar on the outside and inside? Or do I need to disassemble the oven and redo the joints completely? Any advice would be helpful. Also, is there another material I should consider?
Thanks in advance,
From: Jim Buckley
Sent: Tuesday, May 05, 2009
To: Vin Jannetty
Thanks for the pictures, including the one of the first oven your built.
I think the stone veneer over your oven cracked because there was no air space or compressible insulation between the stone and the oven liner to allow for thermal expansion. We have found that the liners do expand and contract and are likely to crack so, to keep the outer shell from cracking, you have to isolate it from the inner liner.
If patching the cracks doesn't work I would remove the stone and then cover the oven core with mineral wool or even regular fiberglass insulation, then some metal lath and a coat of mortar or stucco. Finally, re-lay the stone so that it doesn't touch the inner liner including the oven entrance tunnel.
All this may only be marginally successful since it is hard to seal the stonework so that no water gets in it. That's why many traditional ovens have roofs over them as in the pictures at http://www.rumford.com/oven/Italianoven.html and http://www.rumford.com/oven/Apolloni/Apolloni.html