I usually do not buy things on impulse, but today I bought a case of Kaowool board for $50 off a Craigslist.  The case has 128 pieces of 18" X 3" X 1.5" thick boards in it.  I am planning to build a new forge this winter using blanket, not board, and 2" not 1.5",  and kind of round in shape, so now I am wondering what could I do with it.  Any suggestions?     

My idea cut the board into strips and lay them out in your forge shell around the inside and then a second layer, staggered, and top that with some hard refractory. Think of a whiskey barrel

Did you forget that you can use rigidizer to "glue" the pieces back together, and build anything you like with them? Don't forget to heat cure the parts after they're glued.

The first furnace I built followed the format of the glass blowers' glory holes, and used 75mm (3") strips of ceramic blanket packed like masonry arch blocks around a section of a 50 gallon oil drum.  It would not be a disadvantage for you to make the chamber that way. At 3" wall thickness you could have an 18" long by up to 61" diameter chamber.

Alan

I did not know I could glue it together with rigidizer, that's a pearl.  I was going to call someone in a Pottery Supply house and ask them.   Alan, thanks for calculating how big I could make something with this stuff, I have been thinking about the arch concept, I have a band saw that once set up correctly could cut those blocks into the shapes I need, Although all I need is about a 350 cubic inch forge. 

Just cut them into the arch shape but be carefull of the dust created by cutting the board(even if you have a dust collector)

That seems like the best solution for your materials and i didnt even think about the rigidizer as glue in that situation

On second thoughts...

Given your resource, I would consider what shape furnace it would make most efficiently that would suit the type of work envisaged. Preferably without having to cut or modify them, or at least keep that to the minimum.

If you have a power hammer you can make use of long heats for tapering so two 18" long furnace modules would be good. Using one 18" module by itself for shorter heats.

I would be inclined to pack a couple of layers of boards on flat along the axis of the tunnel for the floor,  and again on flat to give you vertical sides which can be corbeled top and bottom to give you a flame swirl. The corbels could be trimmed at 45 deg. to give a smooth transition. You would only need to bevel the top corbels, the off cuts could then be glued in place on the bottom ones using Mikey's suggestion. The roof can be made with the boards laid on edge spanning across the axis of the chamber linking and fixing the corbels. A squashed or squished octagon depending whether you needed height or width for your projects.

Alan