Polyurethane coating is flaking

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Q: We have a guest house with pine floors. I have sanded them, applied and oil base stain, then went over them with a polyurethane. I applied about 4 coats of poly in 7 days time. The floors looked great for about a month (they weren’t even walked on) and we had a cold snap in weather. I noticed my floors had almost a frost look to them and they were flaking like crazy. Can I just buff the floors with a screen and redo the poly in a day instead of a week? I am learning that I should not of let them dry that long between coats. The floor scratches like crazy.

A: If the coating is flaking seriously you will have to start over. It’s likely you have flaking between all the coats between the first and second all the way up to the fourth. What you have here is lack of adhesion. Adhesion is attained between coats by applying a coat of polyurethane, allowing it to dry and then thoroughly buffing or abrading the coating with a fine abrasive. Essentially you are applying a fine scratch to the finish to allow the next coat to grab. This has to be done between each coat. You will know if a coat of finish is dry enough to proceed if it turns to a fine powder as you buff it and you aren’t having the finish roll of in little strings or clogging the abrasive. 3 coats of finish initially on a stained floor is plenty to start with.

Follow-up Q: Can I do this with just a screen buffer? I am thinking that a sander is to much. I don’t want to pull off the stain.

A: You can certainly attempt it as a last ditch effort before going the extreme but necessary route of total resand. The difficulty is you don’t know for sure on where the peeling starts. Is it failing from the second coat up? You will likely have to screen it fairly heavily, removing a lot of the finish and so there is a very real risk of cutting into the stain with the screen.

Related Q: We have white lines where the polyurethane looks like it is flaking off. The floor was stained with Miniwax and an oil based polyurethane. The main areas of stain were applied at least five days before any polyurethane was applied. The polyurethane was applied in three consecutive days. We have been using a cleaner that contains ammonia and washing the floors every two weeks. Could this have caused the white lines? If not what could be the cause?

A: It sounds clearly to me you don’t have adhesion between coats. This is achieved by thoroughly buffing each coat, that is scratching and deglossing prior to applying another coat. It is really a mystery to me why you waited so long to start applying the finish coats on the stain and why you would be using such a strong cleaning solution in the meantime. Preparation is everything. Clean environment. Good temperatures. It seems clear to me this has not been professionally done.

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