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Building Tips and technical articles. => Paint and finishing => Topic started by: Perry Rose on August 18, 2020, 08:37:54 AM
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I ran the dehumidifier until the humidity was lower than the machine was able to read. The plane was in the room all the time. It did raise the temp. in the room to 90 degrees though. I put two water/dirt filters at the gun and have about 15 loops in the hose. I sprayed a small section of the wing tip bottom and the clear blushed in the open bays only. The sheeted portions didn't blush. I figured there may be moisture in the hose so I put some clear, the same stuff, in a Pre Val thing and sprayed a bit more. Again the clear blushed in the open bay only. Dry out the wing internals? So I'm left with adding retarder which should be here this week or the clear may be tainted. I used all Randolph butyrate dopes and thinners. Does anyone have a cure for me. (I know there is no cure for me it's for the blushing)
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Retarder can help. I've also shot thinner on a wing (lightly) to allow release of moisture. In high humidity, lacquer gets tricky.
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Don't tell any dirty jokes until it's thoroughly cured?
It could just be that the air is so warm that the dope dries too fast on the open sections.
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I had a problem with blushing on a Brodak FW 190 that I sprayed this spring. It was my first time spraying dope. Since I have to spray outside I waited for the early afternoon warm-up and the accompanying RH drop on a calm day. It was in the low 80's when I shot and I had blushing right off the bat. Scratching my head as to how to get rid of the blushing after the fact, I grabbed some Nu Finish Scratch Doctor Clear Coat Scratch Remover applied to a soft rag and was amazed how easily the haze was removed. I have found that in my opinion I am better off spraying in cooler temperatures with higher RH than the other way around. 90 is way too hot for me. I've since found that on average a 50% dope mixed with a 50% mixture of 30% thinner and 20% retarder works well for me. I like to start mid-morning with the temps in the 60's and no warmer than 75. I have noticed a lot of variation in the dope viscosity of newly opened cans so ratios may vary.
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Per Randolph:
Blushing occurs when humidity is over 50%.
Cure:
Wait for lower humidity.
Paint in an air conditioned de-humidified building and take beating from your wife.
More retarder.
I'm fighting that war now. The dark blue on top looks OK. The white bottom shows some blush. I can live with that.
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When I used Dope I cured this problem by adding or replacing some thinner with Sig Brand Retarder. I have no idea if it is still on the market.
John L.
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I agree with Randy. So far, spraying thinner so that it settles in a mist has always removed blush for me.
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When I used Dope I cured this problem by adding or replacing some thinner with Sig Brand Retarder. I have no idea if it is still on the market.
John L.
Randolph retarder is still around. I buy it by the gallon. It works good with lacquer thinner.
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... I have noticed a lot of variation in the dope viscosity of newly opened cans so ratios may vary. ...
If you're really going to be scientific about it you need to get a viscosity cup. Note that I'm not that scientific about this...
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Could be moisture from your compressor. Even if you use a moisture trap. For my set up I start by running the compressor with the drain valve open, and use an air gun on my hose with the trigger taped down to drain moisture from the line. Let this run for 10 minutes. Then close the drain valve, remove the air gun and always use a proper respirator. Kevin.