I have made a largish-sculpture (prob. 20 lbs after bisque firing) and some wall pieces, The wall pieces are slabs with shallow "walls" (about 1.25") so they stand clear of the wall and the lugs/wire for hanging are hidden. I bisqued 1 wall piece flat-side-down on a thin waster slab of the same clay body and then glaze-fired it flat-side up on the same waster slab and it worked great! (Well, the waster broke, but that was the point.)
The waster slab I put under the sculpture broke into about a dozen pieces, so it isn’t re-usable. I’ll roll out another waster slab for the glaze firing, but I don’t know if I’ll should bisque it first.
Additional question: one of the waster slabs I made for a wall piece broke when I moved it. It’s about 17-18" diameter, and a piece along one edge about 1" wide broke off. The wall piece should be almost completely supported by the waster since it’s a little bigger than the piece. Do I need to make a new waster slab? Should I put the broken-off bit next to the rest of the waster?
Other, possibly relevant into: The wall pieces are bisqued at ^1 and glazed at ^04; it’s a ^5 clay. I’ve fired hundreds of wall pieces made from this clay at these temps and it works very well for what I’m making. I use full shelves. HOWEVER, these are the first I’ve built with the walls/rims — the others have all been completely flat and I fired them on grog, no waster slab. The sculpture is a ^04 clay, so bisque firing was to that temperature and I’ll glaze fire it at ^04, too.
Final question: do I need to put grog under the waster slab?
Thanks for your advice!