How humid is too humid to paint?

I live in south-central Indiana, and it has been so humid lately. I've got a couple finished rockets I'd like to prime and paint, but I'm afraid it's too humid for spray paint. What's the general humidity level you think it's OK to paint? I had some weirdness with a black paint that I later realized was due to high humidity.

lcorinth said:

I live in south-central Indiana, and it has been so humid lately. I've got a couple finished rockets I'd like to prime and paint, but I'm afraid it's too humid for spray paint. What's the general humidity level you think it's OK to paint? I had some weirdness with a black paint that I later realized was due to high humidity.

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With my Painting Skills and Luck, any Humid is Too Humid.

It depends on the paint formulation, but there's no real reason you can't paint when it's humid if you use the right stuff. If you Google for "humidity and painting cars" you can find a lot of fairly relevant discussion. There are two physical effects in play:

1) Fast solvents or reducers that evaporate quickly, cooling the painted surface. When the relative humidity (RH) is very high, it doesn't take much cooling to cause moisture to condense on the painted surface (bad!). To avoid this you have to use paint with slower solvents that don't flash off as quickly. Pro paint systems offer different reducers for varying conditions. With rattlecans you just have to experiment. Lacquers will probably cause the most trouble. OTOH the hotrod crowd says you can paint with urethanes even when it's raining.

2) (if using a spray gun or airbrush) Condensation in your air line due to expansion after the compressor. When you are compressing very humid air the expansion will cause more condensation. Best practice is to have a moisture trap *at the gun* and to favor shorter air lines.

TopRamen said:

With my Painting Skills and Luck, any Humid is Too Humid.

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I second that! I have no painting skills whatsoever so it makes no difference...

If using spray cans..read the instructions.
The answer you are looking for will be there in very,very,very small print.

I live in Florida, it is always humid. I still paint, and with generally good results. One exception though, clear coats. Humidity is a beooootch with clear coats. Except the ridiculously expensive Testors. I have gotten very good at a formula involving Future, Mean Green Cleaner and a spray bottle that I do most of my clear coats with now.