I had painted my dash before I put my DMT wood grain on , so I had a good surface. If your wood grain is the thin plastic like mine is, then it is probably not very critical. Just sand off the loose stuff and make sure it is clean and not oily from amour all or something like that. I spliced a piece in my dash and the DMT wood grain covered beautifully
If it is a decal, then surface prep becomes critical, as everything will show through.
