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Author Topic: Humidity?  (Read 1034 times)

Offline Paul Taylor

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Humidity?
« on: March 25, 2013, 05:11:06 PM »
At what percent is it safe to spray dope?
My memory is about gone. Im going to write this on my spray gun.  LL~

Is it 30% and below?
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Offline Tim Wescott

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Re: Humidity?
« Reply #1 on: March 25, 2013, 05:19:04 PM »
That doesn't sound right.  It seems to me that the number must be higher or no one would be able to spray dope in the Willamette Valley.  Whatever it is, though, if your paint is too embarrassed to be painted that day, you can always add retarder (that's retahdah if you live in Wallingfud, CT).
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Offline Allan Perret

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Re: Humidity?
« Reply #2 on: March 26, 2013, 07:31:11 AM »
50% or less.
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Offline john e. holliday

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Re: Humidity?
« Reply #3 on: March 26, 2013, 08:28:57 AM »
Temperature has to be factored in here.   I put the last coat of clear dope on my Thirteen in less than 50 degrees F and all the cloudyness that was there disappeared.
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Offline Tim Wescott

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Re: Humidity?
« Reply #4 on: March 26, 2013, 09:34:16 AM »
Quote from: john e. holliday on March 26, 2013, 08:28:57 AM
Temperature has to be factored in here.   I put the last coat of clear dope on my Thirteen in less than 50 degrees F and all the cloudyness that was there disappeared.

That's interesting.  Temperature is going to act like retarder, but it's going to make the water evaporate slower, too.  I wonder if it has more of an effect on the thinner than the water?

Also, for the same outside humidity, the inside humidity in a heated space will be lower as the outside temperature goes down, even if your space is just heated parasitically, like an attached but "unheated" garage.  That's because the amount of water needed to reach 100% humidity drops dramatically as the temperature goes down.
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Offline Mark Scarborough

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Re: Humidity?
« Reply #5 on: March 26, 2013, 10:44:21 AM »
Quote from: Tim Wescott on March 26, 2013, 09:34:16 AM
That's interesting.  Temperature is going to act like retarder, but it's going to make the water evaporate slower, too.  I wonder if it has more of an effect on the thinner than the water?

Also, for the same outside humidity, the inside humidity in a heated space will be lower as the outside temperature goes down, even if your space is just heated parasitically, like an attached but "unheated" garage.  That's because the amount of water needed to reach 100% humidity drops dramatically as the temperature goes down.
I think you will find it has more to do with the paint staying "open": longer allowing the moisture to escape,,
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Offline Randy Powell

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Re: Humidity?
« Reply #6 on: March 26, 2013, 05:04:01 PM »
I've shot color coats as high as 85% humidity. Sometimes get a bit of blush but shooting some straight thinner (lightly) reopens the paint and allows the moisture to escape (as long as you don't wait too long). I try to wait for decent weather for top coats. And, of course, you are much better off and end up with a much more predictable process if you shoot below 40% or so. But it can be done higher. Sort of depends on your time table, I guess. You do what you can with what you've got.
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Offline Dennis Toth

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Re: Humidity?
« Reply #7 on: March 26, 2013, 07:45:10 PM »
Paul,
It depends on the type of paint you and the reducer/thinner are using. Generally anything under 70% will be fine with dope, LusterKote and Rustoleum. For some auto paints you could go up to to 75%. For the spray cans check the instructions for the humidity limits.

I usually mix my dope at least 50/50, and final clear at 60/40 thinner to dope. A couple tips that make it a little simpler. Go to Walmart and get a combo temperature - humidity gauge. Timing of when you spray is important, in high humidity areas, I find that if you watch the humidity as the day warms usually around 11 am it drops for a few hours, that's when I spray. Also if you are in a "must paint" situation and can't wait you can add some "retarder" but be sure it is either Sig, Randolph or Brodak retarder and don't use more than 8% or it will never dry solid (it will be rubbery). Good luck.

Best,              DennisT
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Offline EddyR

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Re: Humidity?
« Reply #8 on: May 18, 2013, 11:01:16 AM »
Stop using dope. Use Duplicolor Clear Lacquer from the quart cans,not spray cans. It is the same price as dope maybe cheaper. Any dope or Lacquer thinner will work in it. It will work with any dope under or over it. Use one last coat of clear fuelproof dope over it to protet it from exhaust residue. I have used it without the clear dope over it and it started to get soft after a year of use. It will not shrink and pull fillets. I stopped using dope five years ago. It is the consistency of the old Aero Gloss. I use shrinking dope to pull covering tight and then switch to Duplicolor. I spray it in very humid conditions and no blush.Also Duplicolor Lacquer thinner is only $15-17 gallon and it works well in dope. Most auto stores sell it. #^ #^ #^ #^ #^ This plane all Duplicolor.
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Offline Bob Hunt

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Re: Humidity?
« Reply #9 on: May 18, 2013, 08:02:26 PM »
Or use a much higher quality paint that has many more color choices: Dupont ChromaBase system. No issues with humidity!  %^@
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