Sanding Polyurethane

[Thomas Penrose]

I am in the process of applying four coats of oil based Varathane semi-gloss floor finish on a newly installed white oak floor. I have applied the first coat, and with the temperture inside the house at 65 degrees, the stuff is dry to the touch after 24 hours, but after 50 hours I still cannot sand it without gumming up sandpaper or sanding screens. From what I have read, the finish should be dry enough that the sandpaper should create dust, and not gum up. I was going to rent a screen buffer to do the whole floor, but at this point I have no idea when it might be dry enough for me to do this. Anyone have experience with using oil based polys during the cooler months of the year, and how long it takes the stuff to dry enough to sand it? I can use sandpaper, screens, and steelwool to kind of knock off the dust specks and general roughness, but it is not at all like sanding on a finish that is truly hard and set up. Even if I really cranked up the furnace, could I expect the stuff to get hard without it taking many days for that to happen?

[Rick Thom]

That seems really slow drying. Perhaps a few more degrees warmer and a room fan (air circulation) will help it thoroughly dry.

[Jim Becker]

I think Rick may be correct about the tempurature...try and raise it. Also check the working temps listed on the finish container. It's really important that you can accomplish the sanding/screening between coats as polyurethane hates to stick to itself without first being abraded.

[Steve Wargo]

Perhaps you applied the first coat a little too thick. I've not ever used Varithane, but I know that with the General finishes urethanes I have the best luck applying multiple thin layers. rarely takes longer than 24 hours to dry enough to be scuff sanded.

[richard fisher]

this is strange. i just posted about the use of varathane. i am not familiar with it but i bought some on a sears hardware store closing. i used it on my workbench and it dried in a few hours. shop is in the garage with a temp. of about 50 degrees. i put it on real thick and it dried ok for me.

[Bob Johnson2]

I run into the same thing when I use poly in the winter, or even cool damp weather at other times. I have started to move it up into our sun room (solarium?) for a couple days so it can cook. The sun beating on it for a day or so does the trick. I've had it in the non sandable state for days. Don't know what the max would be as I move it into the sun.

[Thomas Penrose]

Thanks for the suggestions. I think it is probably a combination of the weather/humidity here in Western Oregon, and it being the first time I used a lambswool finish applicator. I probably got the finish just a little bit liberal in some spots. However, I noticed tonight that I get some gum spots forming on my sanding screens and sandpaper even when sanding the thinly applied areas, although for the first time I am also creating some sanding dust as well, 60 hours after I did this first coat. I switched to some 00 and 000 steelwool, and was able to abrade the surface and knock off any rough spots pretty well this evening, so I guess it was just a matter of waiting long enough.

[Rick Thom]

Thomas, take heart. I think you will find that subsequent coats with dry progressively faster with each coat. Main reason being less penetration of the preceeding layer.
I do most of my woodworking in the basement of my old house (2' thick exposed stone walls). When the air is a little damp and cool, such as is often the case in spring and fall, that first coat of finish can take forever to dry it seems. I often end up getting out my quartz lamps or bringing the project upstairs. More than once I've pitched what was probably perfectly good varnish out believing it to be deteriorated and lacking driers or something.

[Marcus Ward]

I did my floors with the same finish and didn't sand the first 2 coats, just applied them within 10 hours of eachother. My father in law gave me a tip. He said after the second coat hit it with some steel wool and just knock the blush off and then apply the next layers. It's really tough to get a floor finish as smooth as the finish on furniture, I don't know why, but every hardwood finish I've seen has brushstrokes in some spots but you really don't notice it. My floors are 65 years old and have a lot of character - lots - and I prefer it that way. It looks more interesting than plastic fantastic laminate. My 2 cents.

[Thomas Penrose]

I did see on the Varathane can that you can re-coat without sanding if you do it within 12 hours. However, due to the cool weather and humidity, my floor is still a bit too tacky to re-coat even after 12 hours. I wonder if you could re-coat without sanding at any time, just so long as you did it right after the finish has set up enough that it felt dry to the touch, even if this took 16 hours, etc.