My father and I purchased 4 12x12 pieces of 3/4" plywood and the same polyurethane you showed in the video. We had an extra melamine table that I am allowed to make a mess with. I tried to work on the table, however, I believe it is nonporous and the clay was sticking like crazy. Since I am visually impaired and wouldn't put even coats on the boards he offered to help me but asked if I was sure that was what I wanted. I am a little confused because my understanding is you want a porous surface to work on so your work doesn't stick. Won't putting polyurethane on it make it nonporous and thus stick?