I am going to do a tiled wall hanging. Can I just tile directly to plywood (like attic flooring plywood)? Or do I have to add some kind of sealer to the wood first?
Thanks

Dont use any sealer on the wood it will reduce the bond of the adhesive. It should be real plywood, not pressboard, flakeboard or OSB. Get a thinset that has a lot of latex in the bag mix or a thinset with no latex additive, but you add it in to the powder yourself. It is the latex that will do the bonding to the plywood. For a wall hanging the plywood should be at least 1/2" thick so it doesn't twist in your hands and cause the tile to break away.

Thank you Tileguybob! You're the best!