I have used aerated concrete block for my advanced sculpture students to
work from. It is available from NASCO in blocks that are 2 feet long and 8"
on a side. The material is easily chiseled, dremeled, and drilled. A
variety of finishing techniques can be used including staining over primer
or using texture spray right over the raw concrete. A clear sealant can
then be used to protect the finished sculpture and give it a sheen.
I typically have 2 students split a 2' block, scoring and chiseling 2X
around the mid point of the block until ti breaks into two 1' X 8" X 8"