We are refinishing floors in a 1957 house and the floors are severely stained with dog urine. We have used a drum sander and taken The first 2 coats off. We have tried hydrogen peroxide, bleach, spot shot, folex, and now wood bleach. The wood bleach is lightening them some but not removing them completely. The hydrogen peroxide did The same. These are stains from the last 35 years or so when they were covered with carpet. Any other tips or tricks out there.

You can only bleach out so much from stains that have been there for so long. About the only thing you can do is to try sanding deep enough to remove the stain (which may not be possible).

The only real fix is a partial or complete flooring replacement. Staining does not work, as even dark stain tends to highlight the urine stain areas.

Thanks. I will try sanding 1 room and see what happens after the bleach.