I have been using outdoor polyurethane on several projects. I am using the Minwax brand. I have heard from two people that have my projects that the urethane is peeling. What do you think the cause of this could be? I wait no less than 12-24 hours before re-coating. I put 3 coats on as recommended and I sand lightly between coats. I also use a rag dampened with denatured alcohol to clean the sanding dust off between coats. I don’t soak the rag or the piece, but other than that, I follow the instructions on the can. I don’t think the cans of urethane that I use are very old. I live in southern California so we don’t get much rain and no snow. I am perplexed at what I am doing wrong. Any advice you can give me will be greatly appreciated. – Eric Levine
Chris Marshall: I’m no opponent of polyurethane; it gets plenty of use in my shop, too. But maybe it’s time to venture beyond poly for some of your future projects. Both lacquer and shellac cure quickly and well in hot, dry environments. They offer decent performance characteristics for indoor projects, and they’re certainly widely available at home centers. Both also are easy to repair, and one layer bonds readily to the next, unlike poly. Give these a try and you might find a whole new avenue of viable coating options to add to your list.
Tim Inman: Polyurethane finishes have tremendous durability characteristics. Their major shortfall is their lack of good adhesion properties. They don’t stick well – to the surface they’re on, or to the layers themselves. Are you using an oil-based stain? If so, it might not be “dry” before you’re applying the finish coats. That can influence inter-layer delamination (peeling). Another issue could be relative to your location. Polyurethane requires moisture to set or cure. Usually, 40 percent relative humidity is recommended. In southern California, that might be hard to achieve. If you finished your projects at a time when the humidity was very low, the finish may simply not have been cured out well enough. What to do? Make sure you have higher humidity in the air when you finish. Use a “swamp cooler,” add some mist, or do whatever it takes. Once the finish has cured out, extra humidity would no longer be needed. Finally, extreme heat/cool cycles can influence peeling. Is the project sitting in or near a window or outside? That could be the fatal blow, too!