Troubleshooting Uneven Sheen in Lacquer

Too much thinner can reduce the proportions of flattener, resulting in uneven sheen and excessive glossiness. April 20, 2011

I am spraying Sherwin Williams lacquer medium rubbed effect clear coat over a dark toned lacquer and I am getting an uneven sheen. Lacquer is thinned to about 45% and spraying at about 38 psi. Any ideas? The topcoat was mixed well and when the panels are lying flat, the sheen looks uneven. When I stand them up it does not look as bad.

Forum Responses
(Finishing Forum)
From contributor B:
If you are sure the material is well agitated, you need to look at the possibility of a blush from moisture or an uneven amount of finish on the substrate. The thicker a lacquer is, the higher the sheen will become. Butyl cellosolve at about a quart to five gallons of finish is typically a good place to start if it is moisture.

From contributor R:
You are probably using too much reducer. With that product you really shouldn't have to reduce at all, but if you do, try using a max of 10%. At this ratio, if the material is not spraying properly, you most likely have too small of a tip in the gun.

From contributor L:
Nice even application is key. Keeping the wet edge while spraying and keeping your coats even and consistent will help with the final sheen.

From the original questioner:
I ended up thinning out the finish and added a little retarder to the lacquer. It laid out nice and even, but know it is a bit glossy. I don't think moisture was a problem, but like I said, the sheen is even but too glossy.

From contributor B:
After getting 4 hours of sleep and re-reading the original post again, I wonder if you had some kind of dry spray? Thinned 45% and spraying at 38 psi may have caused material to dry a little before hitting the wood. Retarder would certainly have helped this.

From contributor M:
I think initially you were using too much thinner. I use this same product and in a quart spray cup I only use about 2 oz of thinner, which is way less than 45%. This would cause the sheen to be uneven. I also think maybe you have added too much retarder. Again, I add 1 1 /2 to 2 oz per 1 quart cup. Even a slight adjustment will add to or reduce dry time, which also has an effect on the glossiness of the finish. Keep working with your ratios until you find the numbers that work, and remember these adjustments will have to be fine tuned as the weather changes.

From contributor J:
Too much thinner. You mention it's a little on the glossy side. Adding thinner reduces the amount of flattening agent by volume and will therefore increase the sheen. 45% thinner is approaching what could be called a washcoat. If you ever need more than 20% thinner, you need to reevaluate your gun setup.

From contributor C:
Have you looked at the spec sheet to see what the suggested thinning ratios are? It might also tell you what thinners are to be used and how much, if any, retarder to use, and it might even give you an idea as to the spray gun settings. MSDS and product spec sheets are a great thing to have on hand - a copy in the spray booth and a backup copy in your desk drawer.

From the original questioner:
I would like to thank everybody who helped me out on this one. My problem the first time was the lacquer flashing too quick. The glossy finish was from too much thinner. You guys were right with the proper adjustments - it's looking good. I think my main problem was that I have never used the retarder before and it makes a huge difference keeping a wet edge. Thanks again!