Polyurethane Floor finish problems-drying time too short!
July 18, 2023 4:30 PM Subscribe
I decided to refinish the hardwood (maple) floor in a small room in our house while my family is traveling. Sanded & stained the floor etc. I bought "Varathane Floor Finish Polyurethane Oil Based Fast Drying. (Clear/Satin finish)" The temperature here is about 70 deg and the poly was indeed drying fast..too fast.
I'm a quick worker but I found that after I applied a small section of the poly, when I went to apply the next section minutes later, it was difficult to impossible to get the sections smoothly integrated as the "old section" had already hardened to an extent that I couldn't get the old and new to flow together nicely. So, now I have some pretty obvious ridges where the brush marks stop/start and also some puddles/pooled areas of poly. (I was frantically rushing and probably a bit solvent-exposure impaired by the time I got to this point.)
I am supposed to apply a second coat. The questions: 1.) should I switch to another brand of oil based poly that's not fast drying? The instructions on the Varathane can don't offer any suggestions for additives to increase drying time. 2.) is there a particular sanding technique I should use to get the ridges down before applying coat #2? I'm concerned that aggressively sanding relatively fresh poly will just make a gummy mess. The instructions call for light sanding between coats, but I need to actually take down some material to get rid of the ridges and puddles.
I'm a quick worker but I found that after I applied a small section of the poly, when I went to apply the next section minutes later, it was difficult to impossible to get the sections smoothly integrated as the "old section" had already hardened to an extent that I couldn't get the old and new to flow together nicely. So, now I have some pretty obvious ridges where the brush marks stop/start and also some puddles/pooled areas of poly. (I was frantically rushing and probably a bit solvent-exposure impaired by the time I got to this point.)
I am supposed to apply a second coat. The questions: 1.) should I switch to another brand of oil based poly that's not fast drying? The instructions on the Varathane can don't offer any suggestions for additives to increase drying time. 2.) is there a particular sanding technique I should use to get the ridges down before applying coat #2? I'm concerned that aggressively sanding relatively fresh poly will just make a gummy mess. The instructions call for light sanding between coats, but I need to actually take down some material to get rid of the ridges and puddles.
Honestly as a woodworker and sometime builder of floors, I wouldn't use a poly on a floor for this reason (and a few other irrelevant ones), they are hard to get down properly and professionals are the only people I've ever seen do a good job. Sanding will go about as well as you think it would.
The only saving grace is that the second coat may flow on the old a lot better and may blend some of the blemishes, so it's at least worth as small trial area.
In terms of refrigeration - think of it this way, the tin of poly would be cold for a while but a 0.25mm smear of it has a huge amount of surface area exposure to the warm floor and warm air compared to a tiny amount of volume. I'd expect it to be at ambient temperature in well under a minute.
posted by deadwax at 9:07 PM on July 18, 2023 [1 favorite]
The only saving grace is that the second coat may flow on the old a lot better and may blend some of the blemishes, so it's at least worth as small trial area.
In terms of refrigeration - think of it this way, the tin of poly would be cold for a while but a 0.25mm smear of it has a huge amount of surface area exposure to the warm floor and warm air compared to a tiny amount of volume. I'd expect it to be at ambient temperature in well under a minute.
posted by deadwax at 9:07 PM on July 18, 2023 [1 favorite]
Response by poster: To follow up for future readers: I was able to sand the disasterous first coat OK. Despite my concerns I didn't have issues with gummy, partially dried polyurethane clogging the sandpaper. I used 320 grit paper to sand it.
I applied a second coat. I refrigerated the poly (deadwax's point about the air and surface temperature being dominant factors is well taken, but I thought it couldn't hurt. Any additional drying time is welcome.) I got a broader brush to apply the poly more quickly, got an OV rated mask to prevent the "tripping balls while applying" issue and therefore I didn't run the exhaust fan while I was applying the poly. I think all the airflow may have accelerated drying during the first coat.
It turned out OK, there are a few spots with some crazing (I suspect coat #1 wasn't fully cured in the thicker areas and caused the crazing) but the floor looks much better than it did prior to refinishing. I could probably sand and buff the crazed parts out OK, but I'll most likely just let it ride rather than generate more dust and work. I wouldn't attempt this again- I would just buy prefinished hardwood flooring and install it.
posted by Larry David Syndrome at 6:28 AM on July 22, 2023
I applied a second coat. I refrigerated the poly (deadwax's point about the air and surface temperature being dominant factors is well taken, but I thought it couldn't hurt. Any additional drying time is welcome.) I got a broader brush to apply the poly more quickly, got an OV rated mask to prevent the "tripping balls while applying" issue and therefore I didn't run the exhaust fan while I was applying the poly. I think all the airflow may have accelerated drying during the first coat.
It turned out OK, there are a few spots with some crazing (I suspect coat #1 wasn't fully cured in the thicker areas and caused the crazing) but the floor looks much better than it did prior to refinishing. I could probably sand and buff the crazed parts out OK, but I'll most likely just let it ride rather than generate more dust and work. I wouldn't attempt this again- I would just buy prefinished hardwood flooring and install it.
posted by Larry David Syndrome at 6:28 AM on July 22, 2023
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posted by Larry David Syndrome at 7:26 PM on July 18, 2023