I made a clay handbuilding desk out of a 2nd hand wood computer desk/table. I sanded the finish down to bare wood, then removed as much texture from the woodgrain as possible with finer sandpaper, but not to the point of burnish or polish. I did not seal the wood, because clay work is easier on a absorbent surface like unfinished wood, or canvas on un finished wood. Clay tends to just stick to non absorbent surfaces, not fun for handbuilding. Think about how a lot of clay tools are made with unfinished wood and I think you'll understand it more intuitively. As for drying, I am a very impatient rebel. I made flat 12 by 12 inch potters plaster boards to stick my stuff on to set up, so I could throw and trim on the same day, or build and decorate.