17 July 2011

Rebuilding the kiln

The broken shelf which curtailed firing 16 gave me a chance to assess the. Condition of the kiln after 15 full firings. I removed the broken pieces of the shelf but couldn't get a whole new one back in it's place. The brickwork has shifted quite a lot with all the expansion and contraction of the firings.

 I had to unbuild most of the kiln anyway so I took the chance and went right down to the base. I had been concerned that the bed of sand on which the whole kiln sits may have eroded away.  But no, that is as good as new. What I should have been worried about was the chimney.
You can see the gap of about 2cm down the left hand corner of the chamber.
The internal chimney wall was listing away from the chamber and in danger of collapsing into the flue. As this wall is free standing it seems inevitable that this will happen and I'm lucky that the floor shelf went first.
These are fire bars at the rear of the fire box,  pretty well fused by ash, embers and the effects of the soda going in that way. All the soft brick back wall of the chamber was also very crusty. Time to reassess the soda?  The soft HTI bricks don't like it. I rebuilt that part using all the spare hard fire brick I had, taking some from the front of the fire mouth.
The chimney wall is strengthened by laying the bricks flat and increasing the size of the pillars on which they stand even though this reduces the flue area, and by tying the top course of brick into the side walls of the kiln. The chimney is also taller than the original design by 2 courses which takes the smoke away more effectively. Two firings later and it doesn't seem to be affecting the firing except perhaps for the better. It seems to climb more smoothly but perhaps that's because I've learnt not to get distracted.
The cooling has slowed down now that the new iron framework holds the fibre more snuggly to the walls. The iron is a little flimsy and will need modifying but it works well enough, especially the door.
All in all the rebuilt kiln is an improved one but I'm not sure I want to rebuild it every 15 or so firings. And of course it's just not big enough.........
I was at Aberystwyth a couple of weeks ago for the International Ceramics Festival. Had a brief chat with Joe- Mr Kiln -Finch.........

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