Q: I have two problems after laying down my first coat of polyurethane on my refinished floors. First, despite everything I read, I stupidly allowed the salesperson from the local hardware store to take the gallon out of my hands and put it in the paint can shaker.
Consequently, I of course got tons of little air bubbles that once lightly sanded turned into little pock marks filled with fine poly dust from the sander.
Second, I used a hand sander with 220 grit paper to lightly sand after this first coat. What resulted is a floor full of whitish abrasion marks from the sander. Visually, it looked pretty good after the first coat, but now that I sanded.. I’m afraid that maybe it did not cure all the way? I don’t know. I am so afraid to do anything now.
I used fast-drying satin applied with a roller then immediately a fine bristled brush. Had good ventilation though temperature was pretty low (like 50). Waited 20 hours before sanding.
A: I know I have no need to mention that such coating should be stirred, not shaken (to paraphrase a Sean Connery line). Also, it is far too cold in the room. You need to bump up the heat to around 70 anyway. Good ventilation is not something you want while you are first applying the coating. After it has flowed and started to set up it is ok to add ventilation. It depends on the particular coating what abrasive grit is used but anywhere from 220 down to 150 is generally what I use in the form of a screen disc on a polisher. I use that for the main part of the room and go on hands and knees with 120 grit sandpaper and lightly but thoroughly sand the edges. Some finishes roll on amazingly, such as Poloplaz Primero. Other finishes will bubble if you use a roller and the general applicator of choice is a brush for the edges and lambswool for the main area.
Follow-up Q: Thank you. I am pretty upset with allowing the salesman to shake the hell out of the can. But, here I am. I had a window open and a whole house fan on so it was really sucking. I should have said that the white marks, though caused by the sander, are not abrasion marks. They are actually very smooth. It’s almost like the poly didn’t stick; like air got between it and the wood. Here are some photos of what the floor looks like at present. I am hoping you won’t tell me that I have to sand down to the wood and start over
A: That is how polyurethane appears when it is lightly abraded. I don’t see any indication of peeling. Believe me, if it was peeling you would see it clearly enough. Having said that, there are quite a few areas that look like you missed with your buffing. Make sure you go over everything again with fine sandpaper. Vacuum and wipe down (I use a microweave mop) and apply another thin coat. Spread rates are usually 500 sq. feet per gallon. Thicker is not better.