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Old 09-08-2005, 08:28 AM
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Brian Martin,Freelance adviser
 
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What causes the paint to "blush"?

On another forum (click here) this came up and I never have known exactly what causes it. You know, when you paint something and it will "blush" when you paint in too cold of weather with a flat non glossy look? It happen all the time with lacquer but would also do it with acrylic enamal and using a SLOWER thinner or reducer would help.

I think it does something strange like the solvent molecules that are rushing out of the paint "hit" water molecules in air and grab a hold of them and then they fall back to the surface. I remember there would commonly be a "dew" on top of the paint when it happened.

Any ideas?

Brian

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Old 09-08-2005, 11:02 AM
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Paint "Blushing" is caused by high humidity. The water vapor gets trapped in the paint as the solvents evaporate and cool the surface. It can happen in hot humid weather as well as cool.
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Old 09-08-2005, 11:11 AM
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I think we all agree on the humidity deal, but I to would like to know why?
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Old 09-08-2005, 11:54 AM
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I'm no brain but it's most likely the dew point temp of the paint.
Dew point being the temp which moisture will condense.
High humidity brings this conversion temp closer to the actual ambient temp as well as (I guess) the "cooling effect" that the solvent has as it evaporates. Like alcohol has when it evaporates off your skin.
Causing condensation to form on top of and mix with the wet paint.
So if you had a quick drying solvent that would speed the process up so to speek by decreasing the paint temp even lower.
Say it was 78* and the dew point was 76* that's a 2* window for moisture to form. The solvent evaporation drops the paint down to 76 and water starts to condense on the surface.

Last edited by Bee4Me; 09-08-2005 at 12:00 PM.
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Old 09-08-2005, 01:47 PM
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Brian,

The truck is a mess in the picture. Problem was he painted it outside.

Of course we all know its caused by water in air or water in line but that is just part of the problem as it needs exposure to carbon dioxide from the air.
What your seeing is the formation of the Carbamate salts having been exposed to the elements listed above.

In basecoats its the moisture being contained by the polyester resins.

Most common with fast reducer, fast activators and not enough flash times between coats.

Not as common today as was in the lacquer days but still an occasional occurrence in some colors of base, although it will occur in all colors you only see it in the darker colors.
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Old 09-08-2005, 02:20 PM
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I had that happen on a truck I painted once on a rainy day many many years ago.. It was black and when I was done it greyish.. Nothing like a redo

BK
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Old 09-08-2005, 02:25 PM
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REDO! Ouch!

What a lot of people don't know is it can be drawn out, with a short wave lamp or a medium wave but takes longer.

Sun will also take it out but slowly depending how much material is on the car we could be talking eight hours of a short wave lamp and 16 for a medium wave.

Minor blushing will normally come out with buffing as buffing raises the metal temp to about 115-120 degrees.

Truck in the picture is worse I have ever seen and perhaps a match and a call to the insurance company is the best way.
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Old 09-08-2005, 03:24 PM
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Brian,
I have read the rest of the post for that truck.

His question is why here and not there.

Because dew sets on the top of the panel first and most important the top is sprayed wetter and heaver than the sides and front panels to avoid runs.

Also asked when to repaint?
The problem he has is the water has made the enamel sensitized and the longer the better as right now this is a very unstable paint.
2-3 weeks in sun would be my choice if he has a good hardener in it.
Anything sooner could be a recipe for lifting or crazing.

If he is smart he would sand now and let set in sun.
Then when ready to paint sand again to be safe for adhesion.
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