Film on finish
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Remedying a blush on finish which can be wiped off but reappears. September 25, 2002
Question
I live where the humidity is very high - 80% most of the time. I use a dehumidifier, but on finish I still get this humid, kind of filmy blush that wipes off and comes back. My shop has no A/C. I am spraying lacquer on some walnut dinning chairs. What could be happening?
Forum Responses
From contributor D:
It's cotton blush and there is nothing you can do about it other than to control the climate (A/C). One solution is to use conversion varnish, which is much more tolerant of high humidity conditions. Or you can move to Arizona where I live and never have to worry about seeing this problem again.
Wipes off and comes back? Wipes off with what? Humidity related blush is a common occurrence. Retarders should be used and you can even spray a thinner/retarder mix over the blushed areas to eliminate the blush without a total re-spray. Mohawk and others offer an aerosol labeled "Blush Eliminator".
From the original questioner:
I do use retarders and there is such a thing as too much. This film is on the outside of my finish and it wipes off with a soft cloth. I took the first responders advice and it helped.
From contributor R:
I am in NY and I have no way of controlling humidity in the summer. It can reach about %80 from time to time. Retarders are good but in my experience over 20% retarder (that kills blush in these conditions) may slow down finish drying time way too much. As mentioned, CV is a good alternative. Also, I had better results with 2-part polyurethane. If you absolutely have to spray Nitro and get away with it in such conditions, you may want to try heating it up before spraying. I've used a double boiler and a qt. cup and for some reason it worked out great with 10% retarder. Try to stay away from fast drying solvents. When solvent evaporates from the finish, it cools it down and causes moisture from the air to accumulate on the finish. If your blush seams kind of oily, it may be excess retarder coming out of the coating also. I even fixed blush by blowing hot air from the heat gun on the surface.
From contributor D:
The 2K urethane solution is perfect. In fact, these coatings harden by reacting with moisture in the air. C-V is your first and cheapest long term solution, but if that fails, the 2K urethane route is very doable and it's the most bullet proof film there is.
Try thinning with butyle acetate instead of lacquer thinner. Also cut back on the retarder and find the best combo to solve your problem.
I'm here on the Texas coast and I've never had blush just wipe off. Maybe something else is going on. Too much catalyst if you're using that type of product.
From contributor R:
I forgot to mention that in this condition your compressor accumulates water at a qt a day rate or so. Just drying compressor tank and airlines isn't enough. 5 minutes after you're done, you're going to have moisture in there again. I spent about $350 on an inline filter and it made a great improvement. On a hot summer day I use to have droplets of water and oil come out of the air cup after 3 hours of blasting lacquer.
From the original questioner:
Since the film is on the outside and not under the finish, I think it is from the large amount of moisture in my shop air. I reduced the amount of retarder and put A/C in the shop - all appears well for the moment.
Just the opposite of A/C, how about raising the temperature in the shop 10 degrees? That will lower the relative humidity in your shop environment. Sure, it's not comfortable. But it works.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor A:
We experienced this on again, off again problem over the years. We blamed everything from humidity to cleansers. It turned out that we were on occassion slightly over-catalysing our lacquer. This caused the haze that could eventually be removed by repeated wiping with a moist (water) rag.
