Controlling Lacquer Blushing
Humid environments sometimes make lacquer "blush." Here, pros suggest ways to minimize blush, and to correct it when it happens. August 30, 2005
Question
Does anyone know of a way to control blushing of spray lacquer in a high humidity environment other than a climate controlled spray room?
Forum Responses
(Finishing Forum)
From contributor C:
Add no more than 5% retarder (Butyl Cellosolve), but if the humidity is extremely high this still may not work. There are other coatings that will not blush.
From contributor W:
I would suggest making the switch to a conversion varnish. We did about a year ago and have never looked back. We get ours from Sherwin Williams, but there are many suppliers.
From contributor R:
What brand lacquer are you using? Are you reducing it before you put it in the gun? If you are reducing it you may try using a more refined thinner, they are not as hot. You want to try and give the finish more open time. I spray Chemcraft, and they make a thinner called compliant reducer. This gives me the perfect amount of open time.
From contributor H:
Butyl Cellusolve may be hard to find, it's on the HAPS list. Butyl Acetate and MAK work well in most all Lacquer formulations and they are not on the hit list. Another good thing with those is they get out of the film quicker.
The key is to retard the clear topcoat. That will keep the film from drying too fast and trapping moisture. When retarding the film allow longer drying and curing times prior to stacking or flipping over to finish the other side of the part if you have to.
If you have blushing on a finished part there are products packaged in Aerosol cans called Blush Eliminator that can be sprayed over the dried film in the blushed area to open up the film to let the trapped moisture out.
From contributor S:
Unfortunately blushing is something that all wood finishers deal with. A lot of it depends on where you live and that correlates to how you deal with it. I live and work in Chattanooga, TN and the humidity here is horrendous. I deal with it in many ways depending on the piece.
Some blush worse than others. The first thing you should buy is some aerosol cans of blush retarder/ blush control. Be careful using these on the finished product though. They have a tendency to cause a halo wherever you spray but are great for coats prior to the last. If you are having a real problem with a piece from the beginning you will probably have to fight it the whole way.
I recommend investigating grades of lacquer thinners from your suppliers. There are some grades that are not as hot and are slower drying. I use benco-finishing grade. I also use a good deal of lacquer retarder in my finish in these conditions as well as some MAK (Methyl Amyl Ketone) which is an ingredient of lacquer thinner that improves flow-out and slows down dry time. This usually does the trick. Once you play with the mixtures and get it right you will figure out what to do to stop the blushing problem. Also, I would recommend the Mohawk blush retarder or Touch-up Solutions. They seem to work the best.
From the original questioner:
Unfortunately I have tried the retarder, but I have not tried the blush spray. I live in the Caribbean surrounded by the ocean and when it rains the humidity goes off the chart. I am using Sherwin Williams’s products and proper mix ratios, but I think I will just have to wait for the weather. Maybe the conversion varnish would be worth switching over to.
From contributor J:
Isn't Mohawk/Star Flash-off Control Solvent straight MAK?
From contributor S:
Guardsman Pro Series Products has a Blush Eliminator in an aerosol package that will take care of it on dried films. Pick up some Butyl Acetate or MAK and add a small percent to your finish and it will help.
From contributor M:
A very fine mist of lacquer thinner sprayed on the blushed area removes it. It is almost like magic. The first time I did it I was afraid I would have to wet down the blushed area with the thinner (which wasn’t the case).
From contributor D:
To the original questioner: For what it is worth, I would say that you need to switch to CV or use up to 8% by volume of Glycol Ether EB (ethylene glycol monobutyl ether). This will leave prevent the lacquer from flashing too quick. However it will not prevent the lacquer from hanging. I am a tech and I would not go anywhere without the EB. The other posts here are also correct, but in my experience in coastal environments the EB will perform the best. I recommend it to all the customers I deal with up and down the Oregon and Washington coasts.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor E:
If you have blush, an Amalgamator (Mohawk makes the one we use) is designed to open finishes and let the humidity evaporate. It's just solvents, but specifically formulated for what you’re trying to do. It also works great for getting water marks, etc. out of finishes in touch up.
Comment from contributor A:
For most lacquers you can add up to 10% retarder/thinner (S-W's) R7K27 or Butyl Cellosolve (R6K25) up to 3%. I agree with the several contributors above in that sometimes you can't avoid blushing in lacquer qualities. Switching to Conversion Varnish worked for me, but I have a pristine, climate controlled shop.
Comment from contributor X:
I had the same problem applying spray lacquer. I read that it was caused by humidity. For those of us who live in the South, waiting for a "low humidity day" could be months down the road, if ever. I found that by placing the piece to be finished in the sun for a while, and allow the wood to warm up, and then spray it, the problem goes away. The warmth allows the moisture to escape before the lacquer dries, leaving a clear finish.
