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Humidity


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#1 mnwildpunk

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Posted 21 June 2013 - 11:51 AM

when is there to much humidity to paint? Right now minneapolis is at 63%

#2 Ace-Garageguy

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Posted 21 June 2013 - 12:10 PM

Different paints react differently to excessive humidity. Lacquer, some basecoats and some enamels will "blush" if shot under humid conditions, but the only way to be certain of YOUR particular paint on any given day is to shoot a test piece, using the materials and spray pattern you want to use on a model.

 

The good news is that you can spray more coats of lacquer over blushing with no ill effects, and the blushing WILL polish off of the final surface...really. Try it on a junk body, on a hot day just after a thunderstorm, when everything is steamy.

 

if you use some paint products (catalyzed two-part urethane clear, for instance) you can get solvent "popping" on a hot and humid day. Excessive moisture in the air will prevent the solvents from evaporating from the paint normally and the surface will skin quickly due to the high temperature. The solvents remaining in the paint will form billions of little gas bubbles in the paint or clear that at first glance look like you sprayed a metallic. They WILL NOT polish or sand out (sanding will expose them as micro pits in the paint) and the only solution is to strip and refinish the whole thing. The 'wetter' you try to shoot the paint to get a good gloss, the worse the problem will get. I once had to strip a 1:1 Cobra twice and respray it 3 times, finally at 3:00 AM in the cool of the night, to eliminate a hot / humid popping problem.



#3 TooOld

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Posted 21 June 2013 - 01:30 PM

Something I learned many years ago from an old body and paint man :  Fill a shot glass with lacquer thinner and set it on your bench .  Check it every few minutes and as it absorbs moisture out of the air it will start to turn cloudy .  The faster it gets cloudy the higher the humidity ,  but if after a half an hour or so it's still clear then it's save to paint .  You learn with experience how much is okay for your particular paint .

 It sounds kind of silly but it works great here since the humidity is rarely below 50 % .

 

And Bill is absolutely correct ,  if you are spraying lacquer and it blushes on you it will polish off .



#4 High octane

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Posted 21 June 2013 - 02:00 PM

In the summertime, I usually end up painting car bodies inside the air conditioned house while my better half is a work. Don't know what I'll do when she retires?



#5 Jantrix

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Posted 21 June 2013 - 03:12 PM

In the summertime, I usually end up painting car bodies inside the air conditioned house while my better half is a work. Don't know what I'll do when she retires?


Get a vented paint booth?