Spraying of Satin Polyurethane

Application techniques to avoid runs or streaks and achieve a deep finish. February 12, 2010

I'm putting on my final coats of satin polyurethane. Wiping is leaving a nice finish, but leaving streaks, probably due to an uneven distribution of the silica. I'm thinking of thinning with naphtha (to speed drying) and spraying with an HVLP. I'm figuring this will even out the distribution of the silica particles in the satin poly. Lacquer isn't an option - way too volatile for my shop. Anyone have experience with spraying poly?

Forum Responses
(Finishing Forum)
From contributor A:
Silica in oil based poly? This is news to me. Did you drop a handful of sand in your topcoat? Thinning 10-20% with naphtha is the only way to spray oil poly.

From contributor U:
When spraying poly, try to spray everything lying flat, because poly runs very easily. Spray the last coat as light as you can so it will dry faster and pick up less dust. (I didn't say anything about using a lacquer based product, which is better in all respects.)

From the original questioner:
Very fine silica particles are added to the finish to diffuse the light, thereby reducing the reflection/gloss. It also hides the grain. But some people like it. Thanks for backing up my thoughts on the naphtha.

From contributor B:
It is a good idea to spray a tack coat and let it rest about 5 to 10 minutes before shooting a full wet coat. That will help prevent runs and allows you to let them dry standing up. This prevents too much trash from settling on the wet surface. I like to shoot a coat of gloss for the first coat to add depth and also a harder finish. Satin can look dead without this step. Gloss is a harder finish because the flattening agents in satin (usually paraffin) are not present.

From contributor L:
I have to use it once in a while for a contractor, and when I do I use the method stated by contributor B.