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Tuesday, 28 January 2014

Building a wood fired bread and pizza oven - Chimney transition and more fire

Last few days have mainly been concerned with making the chimney transition, this part will act to smoothly transfer the exhaust gases to the round chimney pipe and will also contain a flap that can be moved to adjust the flow rate.  Fully closed the chimney damper will enable to oven to be sealed during baking of bread.

The transition section has been made from 2mm sheet steel, cut using an angle grinder and then welded using a cheap stick welder. The shapes were worked out by first drawing it in Sketchup and then transferring the measurements to the sheet steel.

Chimney transition in place
With the chimney transition in place, the curing fires are a lot easier to light, keep it burning and a cleaner burn with less smoke.

The oven dome has also been covered with some temporary insulation, the insulation is a foil faced mineral wool that is rated to 530°C.  I have covered the dome in this as it enables a more even heating of the dome during the curing process.

The curing fires have gradually been increased in temperature, the oven has now been fired for a total of about 24 hours.  Unintentionally, the curing has now been completed, after (I thought anyway!) fire had gone out last night, I completely filled the oven with alder logs.  I had planned to leave the logs in the oven as they had been in the rain, leaving them not dry enough to fire the oven.  Unfortunately there must have been some embers left in the oven and once the logs had dried out they ignited.  When I woke up this morning there was a large hole in the roof of the bakery (fortunately, it did not set fir to the structure) and there was a very small amount of ash where the logs had been.  The fire must have been seriously hot, all the black soot that had collected inside the oven was burned off, even on the reducer dome and chimney transition.  Several hours later the temperature of the brickwork is still over 300°C and the temperature of the hearth insulation transition is at 230°C.  I had intended to spend a few more days gradually increasing the temperature, but I guess the curing process was expedited.  There has been some cracking near the centre of the oven, but nothing more than I had expected even with a proper curing process, some in the brick dome and one crack in the refractory slab that the hearth sits on.