his additional info on the DIY Fast Firing Kiln Design instructions is a modification which will greatly improve the qualities of this kiln type. One drawback of this design has shown itself over years of firing, and that is that the bricks tend to move slightly and eventually bulge slightly into the interior of the kiln. A space between the outer and inner layers of brick develops, which is conducive to heat transfer -- meaning that heat is lost. This gap can also possibly be a problem when reducing the kiln, as air tends to get sucked in through the gaps and exact control of the reduction becomes difficult. However, these are problems that appeared only after several years of heavy use!
Another modification I am suggesting is to place both burners at the flue side of the kiln, instead of at diagonal corners. At art college, the technician there suggested that diagonal placement would give the most even heat in the kiln, however I am not so sure about this any more. In theory, the flame is meant to swirl around the kiln interior in a whirlpool-like fashion, distributing the heat. However, it has been my experience that the flame from the burner opposite the flue sucks a lot of the oxygen from the air entering from the flue, creating an oxidized area, while the rest of the kiln is reducing. How do I know this? Oxidized and reduced bricks on the floor of the kiln have a very revealing story to tell! With both burners at the flue end, the flames will shoot away from the flue, move upwards and arch back down towards the flue. This should also give a more even heat.
The next modification is to put up calcium-silicate sheeting as outer walls, holding the outer layer of bricks in place. The kiln will look a lot neater too. Next, a layer of medium temperature kiln fiber between the outer and inner layers of brick will make the kiln much more efficient, as heat loss will be reduced greatly. In theory, hot-face fiber could be used on the interior of the kiln, however, I do not appreciate kiln designs with exposed fiber walls. The fiber tends to become very brittle with use and it is near impossible to stop fiber particles entering the atmosphere during firings and when loading and unloading the stack. Unless you want to continuously wear a mask when handling the kiln, you would be exposing yourself to quite dangerous fiber particles. These particles are on a similar to asbestos -- not very nice. In Australia, there has been talk about banning the use of fiber blanket altogether. However, if the fiber is wedged between two layers of brick, and thus not exposed to the air and/or mechanical friction, there is little danger. To save stacking space, you might want to reduce the thickness of the cold-face brick by about a quarter of an inch, to compensate for the fiber thickness. The insulation qualities of the fiber will more than compensate for the loss in brick thickness. Actually, you could possibly leave out the cold-face brick altogether, and just use the calcium-silicate sheeting with the fiber and hot-face brick, laid onto the broader side. However this type of wall is probably not suitable for long firings at high temperatures, due to eventual heat loss.
The last modification is to stop the bricks moving by gluing them together with fireclay, ceramic brick cement or a mixture of the two.
Required materials for these modifications:
DIY Fast Firing Kiln Design I
DIY Fast Firing Kiln Design II