*** This post is an edited and updated post from my old website that was originally published in 2007 ***
While writing the series of posts about the 2018 woodfiring I thought I'd reserect this old article from 2007 so that people can see how the kiln was constructed.
After completing my university degree in Manchester, I moved back to Wales in 2006 and worked on the family farm. During the first year I saved up enough money to buy the materials to build my woodfiring kiln. The construction of both the shelter and the kiln took about 10 months during which time I was still working part-time on the farm.
Knowing how bad the weather could get in west Wales the kiln would need protection and therefore the shelter would need to be substantial and have enough space for the kiln and all the firewood.
With help from my brother and my friend Rob (who I met on the 3D Design course during my time at Manchester Metropolitan University) we set about digging the foundations for the kiln and it's shelter in September of 2006.
We completed most of the kiln shelter by November of 2006. It was at this point Rob had to head back to Manchester due to other commitments. From now on I was going to be constructing everything on my own.
I had based my design on Joe Finch's fast fire downdraught kiln due to it's ease of use and it's predictability. At the time I was planning on producing utilitarian ware and needed a certain amount of consistency and reliability.
The kiln consists of of opposing fireboxes with a flue that runs down the centre and the ware chamber situated above. This design makes the most of the heat generated by the firewood.
Construction of the ware chamber began in January of 2007. An angle iron frame was welded together to support the kiln and acts as a guide while building the chamber walls. The frame support will also hold the doors for the fireboxes when finished. The kiln is mostly built from soft high temperature insulation (HTI) bricks which means it fires and cools quickly ('heavy' firebricks are used for the fireboxes, flue, and chimney).
The roof consists of wedge shaped HTI bricks which need supporting during the construction. Once all bricks are in place, the former can be carefully lowered and removed and the weight of the roof is now supported by the angle iron frame.
Flue & Chimney
The flue incorporates both a passive and active damper which this gives control over the chimney draw and constriction of the flue . The passive damper consists of 4 bricks which can be removed from the flue and acts as a way of reducing the draw of the chimney through the kiln. Opposite to the passive damper is the active damper which consists of a kiln shelf which can be slid in front of the chimney inlet to restrict the flow. (In hindsight, I would have put the passive damper in the chimney breast as it would have been easier to operate and also be more effective).
The chimney has a total height of about 18 foot - tall enough to create a strong draw through the kiln. The height was calculated according to Olsen's rule for natural draught kilns, that 'the chimney is 3x the height of the kiln. Where it passes through the roof I made a hood which keeps the rain out but lets air circulate.
Secondary Insulation & Firebox Doors
To maintain the heat within the kiln chamber I clad the kiln in ceramic fibre held in place with chicken wire. Although it doesn't seem a lot, the fibre is very efficient at keeping the heat in and helping reduce the amount of wood I need to use to fire.
The firebox doors were welded together by my friend Rob before he had to head back to Manchester. They have a kiln shelf sandwiched between two layers of ceramic fibre. The lower doors are only used in the early part of the firing, while the upper doors are the main stoking access.
Since building the kiln over 10 years ago it has performed really well. I've also learnt a lot on how to fire it properly and get the results I'm after, but only after getting lots of things wrong...
I have also had to figure out how best to pack the kiln to get the kiln to fire evenly (there will always be about a 20/30ºC difference between the hottest and coolest areas though). It's starting to show a bit of wear now, for example the foil over the ceramic wool is disintegrating, the fire-doors are beginning to warp and the metal on the inside of the doors is starting to thin. Also, I'll need to think about re-pointing the chimney in the next year because of the effects of the West Wales weather.
I have no plans of changing the kiln any time soon as it works just how I need it to, however In hindsight I wished I'd built it ever so slightly taller so that I could have fitted more work in. Apart from that I'll continue using the kiln to create my work and adapt it to suit the direction I'm going in.