Saturday, October 8, 2011

Kiln Geek

Over time I have been getting questions about the construction of my kiln and requests for pics, so without further ado......

I'll start by saying that this was the 15th wood fired kiln that I had built and the smallest. As with anything I create there is experimentation, successes and failures; this kiln was the culmination of all that I had learned and still some experiments within it's final construction. The size was roughly 90 cubic feet of packable space, the rationale for it's size was largely for turnover time, I wanted to fire it more than once or twice a year, one winter I fired it 6 times. The design was based on the bricks that I had, more on that later. It's firing time was; from green ware to cone 11 in 32ish hours using 3/4 of a cord of wood (this was the fastest and least desirable results.) In general I was firing for roughly 72 hours from green ware to cone 11 using about 2 cords of wood, extrapolate that to 9 days and that's 6 cords of wood; this was the most efficient kiln I have ever met and in fact the hard part was to keep it moving slowly, it felt like a race car, it wanted to GO!

Kiln geeks, this is for you. The rest of you can go back to facebook or something.
The body of the kiln was a simple barrel arch with a cast key and flame peeps in the key, one stair in it and one side stoke hole on either side. The stair was double brick wall and backfilled earth with silica sand floor. The fire box was earth and silica sand, the bricks were used only for walls, arch, and chimney.   The walls were built double brick using arch brick and the arch was arch brick as well (this was the first time I had the luxury of using arch brick in an arch and it was so easy it almost wasn't any fun.) No, that wasn't a typo, I used arch brick for the walls; I scored about 1500 arch brick for free. They were in pretty bad shape, if I hit them together they would break into 10 different pieces. I also had, collectively, 300 other bricks of varying shapes and sizes, 30 bags of refractory cast-able, and 4 garbage cans of soft brick pieces, all of this material was free. In fact my cost for the kiln was about $150 for sair set mortar and fire-clay. The arch was a single layer then smeared with fire clay and a layer of fire brick set toward the base of the arch and progressing into soft brick as I moved up the arch. The drain tiles, also free, were meant more for visual and a surface to set things on, they probably offered minor buttress support as they were laid up in mortar.
On top of the soft brick layer was a layer of cast-able and basalt rocks from the quarry on the property, on top of the cast-able layer was broken drain tile set in a bed of regular mortar. This last layer was 
primarily for visual pleasure with perhaps some minor insulation properties. I believe the real secret power and work horse of this kiln was the flu system. I have built kilns with venturi boxes and one with a double venturi box. This kiln had a triple venturi box between the end wall of the body and the start of the straight run chimney, the pics on the left show some of that. One of the venturi boxes was made of castable while the others were made of brick. This is the only part of the kiln where I feel dimensions are critical, the rest is just sort of common sense kind of stuff i.e.: the slope being 30 degrees from fire mouth to chimney exit..... well, a sort of "heil  
hitler" pose gives you the right size of chimney. The first venturi box was a packable space and based on how much work was in there would affect the draw a bit; it did produce some amazing results that I had never seen before too, The red white and blue vase for example.
If you click on any of these pics they will blow up bigger for more detail, this is true throughout my blog. You may have noticed the past tense used here, well, I had to walk away from that kiln a couple of years ago due to a breakup. I live mere miles away from it now and have come to terms with not being able to fire it anymore. I believe it is used as a cat house now and as far as cat houses go....


Cambria Pottery said...

The drain tile on mortar is visually very pleasing

Cambria Pottery said...

I appreciate the descriptions on the specifics of the kiln. It will be useful information to think about.