Breaking in Duraboard

[tom suter]

I am looking on buying possible a pice of duraboard that will fit in the Evenheat Coffin kiln. The guy who owns the kiln has been having trouble with his board. Big bubbles all the time. I took a level to the board and to the the kiln. The kiln was on a 3/4 slope one way an 1/4" the other. I do now have it level. I pulled the shelf out and it had at least 1 /2" warp in it. The level did sit on top of all the kiln post there was three lines of 6 kiln post.
My questions are:
1) is there a breakin firing schedule for duraboard, someone who know someone said it should be broke into cycle of 900 soak cool flip over 900 soak flip over 1200 soak flip 1200 soak before using. Is this true?
2) how many kiln post should be under a 42" x 21" run?
3) is there a different shelf you would recommed?

I am wanting to use his kiln for some larger project and want to make sure I don't run into the same problems as he did.

I assume there is nothing to do to take the warp out of the old board.
Thanks for any info on this trying to spare the pocketbook from bad procdures from the start.
Tom

[Phil Hoppes]

A couple of things to do here. First I assume you have a new piece of Duraboard cut to fit the inside of the kiln. You did not mention how thick it is but I'm hoping that it is at least 1.5 inches. Second, you need to rigidize your board with rigidizer (colloidal silica). This is important as it will bind the fibers on the surface and keep them from becoming airborn. I'm guessing for a 41" by 21" sheet you will need about 1/2 gallon. You should be able to get this farily inexpensive from a refractory supplier. (I'm guessing the same place you got the board from.) I would NOT use any kiln posts. The way to put the rigidizer on is to get a medium knap 9" paint roller and roll it on. I cut open a large trash bag for a drop cloth and roll it on using a regular paint roller tin filled with a liner. That makes cleanup easy. Roll the top and the sides and wait for about 15 min for it to soak in. Flip it over and roll the bottom. If you still have rigidizer left, flip it over an finish it off putting it on the top.

To fire it you can do one of two things. You should make sure it is dry before you take it up high. I ramp AFAP to 500 and hold it for 1 hour. Then I ramp AFAP up to 1400 and hold for about an hour and then shut down. You may have to do this twice as the bottom may not be completely fired out. You can tell if it is still brown. If so flip it over and repeat the cycle. Be sure and vent your kiln when you do this. The other method is to wait a few days for it to dry and then just fire it like I mentioned.

Phil