Greasy substance on unfinished floor

Q: I am about to screen/lightly sand my floors and apply a couple coats of polyurethane. I have done some years ago, but never had this problem: There is a greasy substance which has gotten into the oak hardwood (the finish has been worn off/there’s no sealer) and regular cleaning/washing did nothing to fix it.

How do I be sure to get it out before putting the new finish down? I don’t know if light sanding will remove it.

A: Are you saying the wood in that area has no finish and is totally exposed? In that case, it must be greyed and discoloured. If that is the case, you will need to make sure the wood is sanded clean.

If you are concerned about contaminants you could wipe the area down with alcohol (not Jack Daniels), perhaps apply a coat of de-waxed shellac and then coat the floors.