# Spray Polyurethane - A few questions



## J2W2 (Dec 31, 2014)

Hi,

I am using spray polyurethane (Minwax Satin Fast-Drying Polyurethane Aerosol) for the first time. The poly went on nice, but as I was doing some clean-up later, I noticed the can says to recoat within 2 hours, or to wait at least 72 hours. That really threw me off as I intended to put a second coat on tonight. It had probably been an hour and a half since I'd applied the first coat when I read that. I touched the last piece I had done (it's a base piece that doesn't show) and the poly on it was still very tacky.

I normally use brush-on poly and will sand and apply additional coats after I let it dry for several hours, but I've never waited anywhere near 72. I assume the spray on poly has been thinned with something that will at least partially dissolve the previous layer if it hasn't fully cured? And is it proper technique to apply additional coats while the first coat is still drying? If so, how quickly (since the can says under 2 hours)?

I plan to apply at least one to two more coats, so I need to know the proper way to do that. Since the first coat has been on for over 14 hours now, I'll wait the 72 hours before applying additional coats.

I was also planning to do a light sanding with 000 steel wool, but right now the pieces feel so smooth I believe I'll skip that, unless I notice any bumps, etc., when I really check them out. Is that acceptable? I do not want a shine on this project, and I know from experience that brushing on more than two coats of satin poly, with light sanding in between, still produces a fairly glossy final product.

Thanks for all your help!


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## djonesax (Mar 3, 2008)

This exactly why I dont use poly anymore unless I have to. I can spray 3 coats of lacquer in less than an hour and I'm done. Each coat melts into the previous so there is no need to sand unless you want to.

---Making assumptions here---
Someone else will know better on this but I am assuming that if you spray it again in less than 2 hours, then some of the new coat will adhere to the old coat with no sanding. But after that its past that point and now they want you to wait until its completely hardened before recoating.
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From personal experience, I have never waited 72 hours to recoat poly. When I did use it, I would wait about 6 hours if I remember. I would do it over two days, coat in the morning, coat at night, and coat the next day. Sanding it lightly with 220 sand paper to knock down the bumps, runs, and give the next coat something to adhere to, between coats.

It should not get glossy but you can can always rub it with 000 steel wool and get a satin finish.

David


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## Steve Neul (Sep 2, 2011)

It's called a recoat window and you better pay attention to it. 72 hours is for warm weather. In winter you better give it a full week. There are a lot of finishes that have a recoat window especially rattle can paint. What will happen if you exceed the recoat window is the dried finish that is on there now will wrinkly up like you put paint and varnish remover on it and the only fix would be to put paint and varnish remover on it and remove the finish and start over. What it is, is the solvents in the finish probably acetone is too hot to apply over a nearly dried finish. You have to either spray it while it is beginning to dry or wait until the finish is cured hard enough it can tolerate the hot solvents. 

As far as sanding, use sandpaper. Steel wool will just rub over debris that might be in the finish. Also steel wool is dirty. It breaks down and gets bits of steel all over the finish which is difficult to clean off.


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## J2W2 (Dec 31, 2014)

> It's called a recoat window and you better pay attention to it. 72 hours is for warm weather. In winter you better give it a full week.


 Thanks for the advice Steve. I gave them a week and then applied two more coats about an hour apart.

Everything came out great. I sanded them very lightly with 400 grit before the other two coats. Good to know about the steel wool too - I've seen a lot of posts about using it, but I'll stick with sandpaper.

Thanks again for the help!


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