We have an old 1930's handymans house and are slowly refinishing it. In the mudroom we just recently pulled up the old vinyl sheet tile and found that the floor was made of standard old boards which someone had "insulated" by placing sheets of newspaper over, back in the 40's. I talked to a friend because I have my heart set on placing in groutable 12" square vinyl tile, and he suggested rather than trying to repair the boards and level it all with floor leveler, that I should just go over it with 1/4 " plywood. My question is, should I do anything to the boards before I lay down and start screwing in plywood? I'd rather not have them slowly rot from beneath, or cause an issue because I didn't protect the boards.