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Old School
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Discussion Starter · #1 ·
I answered a finishing question on another forum about lacquer blushing, and finishing problems with spraying, and I thought I'd also share it here.

The major problem with spraying may be in your set up. Many different parts of the system can be a cause. Understanding the process may help you to get better finishes. An air compressor is basically an air pump. When running it is pushing hot air into a container (tank), which fills under pressure. The air going into the tank is hot air. This creates condensation in the tank and water, and other matter gained in the air in the process will store in the tank. This is why you should drain the tank regularly. I do it under tank pressure in order to blow out all moisture and whatever sludge builds in the bottom.

Next in line to check is the filter. It is fairly useless to have the filter mounted right at the tank where the regulator is. You should pipe the filter as far from the tank as possible. The reason for this is that at the location of the regulator, there is hot air under a lot of pressure, that blows by the filter some moisture and debris. If you don't have a long run to where you want to spray, pipe up as high as you can with a drain below to catch the moisture. If you have no room to take off at a 90 degree from that high point, just create a large "U" turn and come back down. What you want to create is to travel the air so it will cool, and get as much moisture out as possible. Remember, just moving the air will warm it.

Ideally, any line you set up from the compressor is more effective if it rises in height until your spray gun, with drains along the way.

Next is your spray gun. I've always used one of those bulb filters that screw on the the handle of the gun as a final filter. Try it, you'll see a difference.

Next is a little discussion on finishes. I'm a proponent of using like materials from start to finish. If I'm using lacquer, all the steps in finishing will be acetone based (lacquer thinner), such as a sanding sealer, and then finishing lacquer. If a stain, or dye has dried that has been applied to bare wood, your steps in the lacquer finish should be fine.

Where you have a problem is when ingredients from different bases have the chance to dance around together. Most of the compatibility problems I've had were due to preparation, rushing, or not being ready with the next step.

Now for blushing. The start of blushing can begin at the point of the tank, If enough moisture is carried out to your line and gets blown past the filter (it doesn't take much), it will merge with the air that enters your gun and...voila...blushing. Or, any moisture that collects in the line to the gun, that should be caught by that neat little filter I already told you about, but wouldn't be if you don't have it.

The mixture of how much air (to the gun), and the air/fluid mix (at the gun), can contribute to blushing, if the air mix is much greater than the fluid composition. Ideally, a lacquer finish would be almost problem free if you could get it to the workpiece without any air. If your air pressure mix is too high, the spray will cause a "drying" before it gets to the workpiece. So, depending on the type of gun you use, it's playing with the fluid/air mix. You do want the mix to atomize sufficiently, so that runs will be less likely.

Next, If the humidity is fairly high, as you spray, the spray pattern shoots through the air to your workpiece collecting moisture that's in the air. I've seen it so bad that mid air I saw the blushing occur when the lacquer carries the moisture to the workpiece. It's like it grabs a little cloud and transfers it .

So, the answer I found to help in the spraying end of all this is to add retarder to each cup. Even if the humidity seem low, it makes the lacquer flow much better. As a mixing note, in general terms, acrylic lacquer thinner can be used in both acrylic lacquer and nitrocellulose (NC) lacquer. Don't use NC lacquer thinner in acrylic lacquer. The term "acrylic" lacquer has nothing to do with water or latex. Furthermore, there are different drying speeds in lacquer thinner. If you're buying from a supply house that carries industrial products, you can buy a "slow" lacquer thinner, that will flow better than a faster dry.

Now for the fixes to your problem. If the lacquer has dried with the blush, you can mix up some lacquer thinner and 20% retarder, with a small addition of lacquer, like maybe 5%, and spray over the blush. It's much better to catch the blush while it's still wet, or hasn't cured. Pure thinner and retarder at that point may resolve it. If it is really bad, you may have to wet sand and respray.

I have since been using water based polyurethane, which has fewer problems, less of a health risk, and finishes off very nice. I get a very good finish with it. If you haven't tried it yet, it could be like a whole new adventure.

129 Posts
I do some touch up and repair work nowadays. Moving damage etc. So I work with shading laq, and clears in the bug bombs.

I ran into this blushing sometimes in New York in the summer months. Now in Florida it is horrific.
I see in my Mohawk catalog a product that is suppose to re flow the finish and allow the moisture to escape. Have you or anyone ever used this? I think my next order will include it to try.
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