Wet Spots in Finish

If excess stripper isn't removed, it can stop laquers from drying properly. August 30, 2005

Question
I am not new to the woodfinishing industry but I am certainly not a know it all. One question I have is about why lacquer seems to lay wet in certain places especially in the bottoms of drawers that I have sprayed or on random spots on the tops of some pieces. I have always misted these spots with some naptha and they seem to go away, but I am wondering what causes it?

For instance, I was working on an old trunk recently that I finished a while back. I set it aside to order some leather for the handles and decided to final coat it and when I finished I noticed that I had some random spots that just would not dry. I tried hitting them with a light breeze from a hair dryer to no avail and I am just wondering what causes this and how it can be avoided. Does anyone have any suggestions?

Forum Responses
(Finishing Forum)
From contributor S:
Sometimes it can be something foreign on the surface prior to spraying that the finish does not like. I would think contamination of some sort. Try wiping the piece with the VM&P Naphtha prior to spraying to see if that helps until you find the source of contamination and are able to eliminate it. Some coatings are touchy/sensitive.


From contributor M:
Are these spots on pieces that you stripped? Or are they pieces that you cleaned and de-waxed and then recoated.

From the original questioner:
These are usually on pieces that I have stripped using Benco B-1 stripper. It doesn't happen consistently making it harder to trace.. It's like the whole entire bottoms of a set of drawers I spray will lay wet for hours. I use a Kremlin MVX gun and a 10-14 pump. I am sort of at a loss for an explanation.

The funny thing is that none of the other parts of the piece do this. They all dry to the touch within 15-30 minutes but these it seems will never dry and some places literally never dry. They always look wet until I mist them with naptha from a spray bottle. I will have to admit I am clueless on this one. Today I promised that trunk to a customer. I sprayed it, set it in my curing area, she came in like five hours later and there were wet spots. I had to send her home and without the piece.


From contributor S:
Wax in the stripped areas, strippers not dry where the wet spots are present possibly, all points back to contamination somewhere. Final wipe your stripped pieces with Acetone and see if that helps.

From contributor M:
You need to do a better job of removing the residue of the remover. I suggest you use Acetone or Lacquer Thinners as your final clean up with steel wool or the nylon rubbing pads. What is happening is that you’re not removing all the stripping residue, and then when you spray you are reactivating that residue.

Sometimes a damp cool cloth wiped over the wet spots may take away (not remove) the wet spots, naptha, or mineral spirits also may work with out affecting your new coating. The key to eliminating them is to clean the pieces better with a solvent.


From contributor R:
To the original questioner: Are you using a catalyzed lacquered/varnish? If so, my experience says it's directly related to the stripper. My experience also suggests that the stronger solvents such as lacquer thinner and acetone don't totally solve the problem. After my last experience I talked with a tech at the company manufacturing the stripper. He recommended mineral spirits since the type of wax was incompatible with lacquer thinners and acetone. So I haven't had opportunity to really test that, but try thoroughly washing with mineral spirits next time and see if that helps.

From contributor T:
The late Jerry Metz routinely advised against using conventional finishes on drawer boxes, and recommended a drawer-finish, which was a wax-based spray. This wax on raw wood doesn't strip or rinse easily, so that could be your drawer bottom problem. Contamination (residue of stripper/old finish) as mentioned is likely the cause of the random spots. A misting and/or wiping with clean cold water is very effective at forcing these areas to dry, although sometimes with a higher gloss than the rest of the surface.

From contributor R:
To contributor T: Do you know why Jerry recommended that?

From contributor M:
It's usually residue of wax that inhibits the lacquer drying. Try passing a damp/wet rag (using water) over the area. Somehow, when the water dries it helps dry the area, and the wet spot usually disappear.

From contributor T:
To contributor R: I believe he was addressing the concerns of blocking, sticking, and odors.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
I have been dealing with wet spots in lacquer for the past 40 years. The difference between finishing virgin wood and doing re-finishing work on furniture is night and day. The tendency to lay a nice wet coat of finish is always present. The problem is exposing the contaminated surface under the finish. Lacquer by its nature dissolves the previous layers or coats so that at the end you have one layer, not multiple coats of finish. I have found that applying several light coats rather than a few nice wet leveling coats is the only way to avoid the wet spots. Even at that you can still have some areas that just won't cooperate.

This is the nature of the beast. I have found over the years that the type of wood also has some effect. Cherry and maple in particular are susceptible to wet spots. I too have found that wiping the area with Naptha and then letting the finish dry for at least an hour or more before adding more finish helps to control the process. The key is to bury the contamination by applying several light coats and then at the end giving one or two typical wet coats that will level and look the way you want it to. Using a good sanding sealer also is necessary when doing restoration work. You get a more solid build with it as opposed to just using lacquer for the sealing process.

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