Finished Block III

And two shots showing how the blocks interlock.

Finished Block II

This one shows the groove.

Finished Block

Here are a couple of shots of the finished blocks. This one shows the tongue.

Cast block

Here is the mold, full of castable. It's been on the cool side here lately so they take 12-24 hours setting up before they come out of the molds.

Pouring

Filling the mold.

Ready to pour

'nuff said.

Dry mix

Materials are mixed thoroughly prior to adding water

The Mix

The castable recipe I am using is 4 parts raw kaolinite, 1 1/2 part sawdust, and 1 part calcium alumina cement. They are shown here prior to mixing.

Brick Molds

I completed the first set of molds. I bought a piece of 3/4" A/C as it strengthens the wedged tenons. I chose to put a little extra time into making these in this style as they will be easier to demold and I expect them to last through many kilns. End pieces will be interchangeable and I will make different side pieces for different lengths. I sealed the inside faces with Tompsons water seal. The mold will create a tongue and a groove in each brick. It is a little hard to see in the assembled mold, but in the expanded photo you can see, on the lengthwise sections, the parts which will form the tongue and the longer 2 x2 coming off the end piece which will form the groove. The groove was made slightly larger than the tongue and both were beveled to 10 degrees. Note that in the expanded photo the piece which forms the groove is upside down in relation to its position in the assembled mold.

Calcium Alumina Cement

The cement arrived last Friday, a major step forward. The guys at our local lumber yard were kind enough to bring up their forklift to unload the truck at my house. I bought Secar 51 from Pryor Giggey in Chehalis, Washington. They had a $600 min order so I purchased 1200 lbs at $0.50 per lb. . I have estimated I will need at least 800 lbs but I didn't mind having to get a little extra. In the background you can see the clay pile and my batch box. Now I need to find some sawdust. Next: Brick molds

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.

Gathering Material

At the end of the summer I was able to gather enough fireclay for a 30 cu. ft. kiln. The deposit contains flint clay from the size of boulders down to gravel and fines. There are two deposits near the main quarry face the contain mainly gravel size particles so, as I have no crushing equipment, we took a 1/4" mesh screen with us and screened the material as we gathered it. In five hours we loaded the pick up with around 5400 lbs. of clay. I figure we probably moved almost ten tons of material total.

Hobart Butte

My current project is constructing a kiln from a local deposit of flint fire clay. The deposit is located on Hobart Butte in the town (to put it generously) of London, Oregon about ten miles south of Cottage Grove. I learned of the deposit while researching local materials at the university library in Ashland, Oregon. The geology section of most university libraries is a valuable resource in the search for local material, especially for stoneware. This particular deposit was thoroughly analyzed in the 1940's as a potential source of alumina and was mined for a time for the production of fire brick near Portland. The main ore body, which averages 30% alumina, is in excess of 90 million tons and the total deposit is over 200 million tons. Fortunately the aluminum industry hasn't figured out how to smelt anything other than bauxite and the deposit remains virtually untouched, The deposit, located on BLM land, composes, essentially, the entire top 1000 feet of the mountain and the old quarry face is accessible by a rather rough logging road. 4wd in the summer and forget it in the winter. The potential for this material to form the basis of a regional craftsman's economy is tremendous. It is the foundational material for the glass, metal and ceramic crafts and could be used for forge liners, smelting furnaces, glory holes, glass batch furnaces, lehrs and, of course, pottery kilns.