Q: I sanded old finish off my wood floors, then put a oil base stain on, and then put a water base urethane on. I lightly sanded the floor next day and put a second coat of poly on. Now I have a few spots flaking.
I redid the floors one more time, the same way, except I sanded the bad spots more thinking something might be causing poly not to adhere. Still having the same problem in same areas!
A: Unless you have used a fast drying stain such as Dura Seal Quick Coat I would think it rather risky to apply a water borne finish the next day because if all the solvent has not evaporated from the stain it can cause peeling. That would then be the contaminant.
Or there may be some type of contaminant in the wood. I’ve done a couple of floors that when I sanded them to clean wood they shortly after started weeping an oil. These were old floors and this was likely linseed oil. I used an oil based polyurethane sealer and had no issue. If I had used water borne, I would expect it to peel off. Of course, Poloplaz has a water borne coating they recommend to be used as a first coat over woods that have high levels of oil in them and this will bond and act as a seal coat.
Follow-up: Can I just lightly sand and put an oil base poly over water base poly?
A: If the water borne coating is sound, not flaking off then yes, you can lightly but thoroughly sand it and apply an oil/solvent based coating over it.