6 June 2022

The work horse is getting a little tired

After 44 firings to cone 11 and soda sprayed in each time my kiln is needing some major maintenance. The original plan of the kiln was modular, so the firebox, chamber and chimney are all seperate structures and can be independently replaced as necessary. So I’m replacing the chamber with all new bricks, replacing the grate in the firebox and replacing the adobe on the firebox and chimney.

When I built the kiln in 2014 I used old bricks, they had all been in two kilns at least previously. Over multiple soda firings the brick creep problem requires more maintenance – basically banging the bricks back into place. The holes and cracks opening up allowed patches of oxidation and the drips from the throat zone and main arch were increasingly problematic, as was the runoff from the walls/bag-wall that was sticking pots in the throat zones and chamber floor.

So this time I splashed out on new high alumina (Shiral 42 X) bricks for the hot face and insulating bricks for the outer coursework (J26). This should mean the chamber will last about twice as long.
The demolition also gives me a chance to forensically inspect the kiln and see where the worst damage occurred and why. Hopefully I’ll come up with fixes that will reduce the maintenance needed.

Old bag-wall
Brick degradation

After taking off the adobe (and mostly keeping it as I can reuse some of it) I checked out the condition of the chimney and firebox, both seem OK and only need minor repairs. The chamber throat wall slowly revealed the amount of bend it had developed over the years and had bent inwards towards the chamber by 60mm. The other walls had remained mostly true and straight. Although the arch had opened up gaps, these never caused an issue and the fibre layers and outer adobe are all OK to get reused.

The firebox floor has been deteriorating for years and so was easy to dig out and relay with old bricks, ready for the new grate. The condition of the concrete blocks behind the throat steps was also examined and they look fine, a tiny amount of decay but no cracks, they are all full of a clay/stone mix.

Throat arch laid

I created a new flexible arch former that follows the curve of the firebox so the throat arch will match it. The new bricks here will make a big difference as this was one area under a lot of stress. A slow part of the rebuilding is getting the levels right as I’m keying new brick into old structures. The whole pad seems to have tilted about 10mm so I’m correcting this at the soft brick under floor layer as they can be ground easily or packed up slightly to level the floor before I start the walls.

Floor levelling ready for insulation block

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