All,

My wife and I are renovating a 115 year old 2-flat (2 apartments stacked vertically) in Chicago.  I recently pulled up the terrible vinyl tiles and masonite previously installed in both the first and second floor bathrooms.  Typically I’d expect the old growth hardwood that is in the rest of the house (and in great shape, but due to be refinished) not to be in the bathrooms – likely removed by a previous owner and replaced by sheet stock or a mortar bed…but it’s there.  It’s slightly irregular, i.e., buckled in one spot, but otherwise it’s solid and salvageable. 

Needless to say the ceramic tile we bought before I pulled up the vinyl is not going to be installed over this (even with cement board) because of the expansion issues.  To get it right I’d have to pull out the hardwood and install plywood, which is not an option right now.   

Any options/suggestions for refinishing/sealing the hardwood to maximize it’s water-resistance?  I’m most concerned about seepage through the floor to the ceiling below (from 2nd floor to 1st and 1st to basement, respectively).  We will still tile the tub surround and may still do the baseboard out of the tile and silicone the heck out of the underside.

Any help is appreciated.