I used a wood plauqe for the base. The only thing that I can imagine adhered it to the wood is from all the pressing on I did while forming it. It's on the good though, I tried to seperate a corner of it after I baked it and it would not budge. It seems to be adhered even better than the last one I did with glue, I had alot of problems with getting it stay flush with the base. I thought that time that maybe the water in the glue was having an effect with the wood. With the way that the wood is from the store it is allready kiln dried so shoud not be to much moisture in it. Of coarse the real test will be come summer time here in GA when the humidity returns, right now it has been pretty much in the 30% relative range.
I imagine that there has to be something in it, If it was real clay, then it would dry out over time and become hard like dirt does. This stuff stays moist in a package that is not air tight. I have had the box I have now for about 6 months sitting on top of the fridge and its still moist. That may be what is getting it to adhere to the wood. I have noticed very little contracting with the drying process. There will be some of coarse because water is being removed from it similar to concrete and it's thin. Thats why I am thinking that the cracks happened where they did. It was areas where I thined it out with the indentions.
Allright, I just realized that I am sitting here pondering the science behind sculpty. I must be bored!