Urethane Separating In Prefinished Floors


Six weeks ago we screened and recoated our prefinished hardwood floor with an oil based polyurethane. We did consult with the manufacturer of the floor first, and they said the foor was meant to be recoated if it was properly screened first. Over the last week we have noticed that the urethane appears to be seperating from the surface between the cracks of some planks. It looks almost like an air bubble in the bottom layer of urethane at first and then in a couple of days it comes to the top layer of urethane and peels slightly. Why is this happening? The humidity has increased recently and the boards are swelling. Is the urethane that got between the planks being pushed up between the cracks? We don’t want the urethane to start peeling off the whole plank.



Dear Bekky

Well I was waiting for questions like this now that the new urethane prefinished floors have been out there for a about a decade. The factory applied finishes vary from brand to brand and they keep their finish ingredients a closely guarded secret. They are generaly coated with what is called in the trade; conversion finishes. Some are cured only by exposure to ultraviolet light others are two component finishes with special hardening components. They all are coated in a well timed factory setting and are exellent coating in themselves. Now in the real world these finishes may have a hard time accepting another coating of a conventional finish. Before coating over an existing finish I always do an adhesion test by cross hatching a small sample area with a razor blade. Apply a piece of duct tape to it and rip it off. A well adhered finish will show now signs of peeling on the hatch marks.

Try this test in a corner of your floor on this finish that you applied so that you can find out if it is actually sticking to the original finish. It may be that it is just not sticking to the edges of the V grooves because these didn’t get screened before coating. Another possible problem is that the coating is too thick and didn’t cure properly especially in the V grooves. But I expect the culprit is the lack of adhesion between the factory coating and yours. Do the test. I’m sorry to say if it fails the test you wiil need to sand the whole floor down to the bare wood (sand out the V groves) and finish with a conventonal finish that you will certainly be able to recoatin the future.

As always your Most humble servant, Joseph, the Wood Floor Doctor.