Testing

To date I have run two series of test of the Hobart Butte fireclay. Hank Murrow has been quite generous in firing my tests. My current intention is to use a homemade insulating castable. My first tests were 2 parts 1/4" to 1/2" fireclay, 2 parts 1/4" to fines, 2 parts sawdust and 1 part 71% calcium alumina cement (by volume). I used the 71% because is was all I could find at the time but for the kiln I will be using Secar 51 a 51% alumina cement. The first series showed excellent refractory qualities but they were a bit crumbly with the larger particle size being the worse of the two. Also, the sawdust I used was coarse end grain shavings which seemed to contribute to the lack of mechanical strength. The second series, shown at right, used 4 parts 1/4" to fines fireclay, 1 part calcium alumina cement and varied the saw dust content using1 1/2 and 2 parts (by volume). I used tablesaw sawdust this time with the fines screened out. This gave a much stronger brick with the 1 1/2 parts sawdust being the better of the two. I still have an issue with fine cracking due to shrinkage but they seem mechanically solid. As I have no way of firing grog at this point, I will construct this kiln with the materials, "as is", and use it to fire grog, along with ware, for the next kiln. The background in the photo is the fireclay we gathered. Test bricks were fired in Hank's shino firing to cone 11.