too humid to paint?

[rick spears]

i know humidity affects the out-come of a paint job. (especially when painting in your own garage and not a fancy paint booth) does anyone here have an opinion or experience with how humid is too humid to paint? thanks, rick

[Tony Roussos]

Re: too humid to paint?

Check with the manufacturer/supplier of the paint you select for advice and additives for humid conditions.

In a garage, I probably would stop at around 90%. It depends on the quality of paint, temperature, skill level, and other factors. If you have a dehumidifyer, run it until you get 75% rel hum. then shut the thing off and unplug before spraying to avoid sparking an explosion from possible paint fumes. If your paint produces combustable fumes, only spray with a combustion proof fan for safety.

What per cent relative 'humility' are you seeing lately? What city and state are you painting in? What kind of paint are you spraying?

I hope this helps.

[rick spears]

Re: too humid to paint?

thanks for your response...i am painting PPG single stage urethane. i am in kansas, and humidity has been 50-80% lately (or raining) so you think up around 75% is still no problem to go ahead and shoot?

[Tony]

Re: too humid to paint?

KANSAS??!!

I was thinking Louisiana, Alabama, Houston, or someplace like that!

I have never shot urethane, so I can't say for sure, but consult the supplier and manufacturer for their recommendations (Additives etc..)

Best wishes. Post Pics when done!

[Art A.]

Re: too humid to paint?

Rick, I'm not a painter so I can't give you advice on painting, but when the PROFESSIONAL painter, from the GM tech center(moonlighting), painted my 65 with lacquer, it was 98 degrees and 95% humidity and it STILL stands tall 25 years later.The shop he painted it in was nothing special, just an old gas station type building. To my surprise, he had two other Corvettes in the same room and was painting all three in the same time frame and didn't get cross contamination----wow!

Art

[Ed Jennings]

Re: too humid to paint?

While "blushing" is mainly a problem with lacquer, other paint types, such as urethane can do it as well. Lacquer is much more susceptible. Any day that "feels" dry, you should have no problem.

[Tracy C.]

Kansas is Good, I'm east of Wichita where are U? *NM*

[rick spears]

Re: Kansas is Good, I'm east of Wichita where are

i'm in wichita, and i'm plannin on painting the final topcoat on my 73 coupe tomorrow..although weather report says "muggy" (thus the question) where are you at?? rick

[Wayne W.]

Re: Kansas is Good, I'm east of Wichita where are

Heck, you can shoot single stage urethane in the rain. Seriously if you can keep your air supply relatively dry, you can shoot urethane in very humid conditions.

[Craig S.]

Re: too humid to paint?

Art - that is the beauty of lacquer...by the time the dust hits the other cars, it is just dust not wet paint... And that 65 does still stand tall!!...... Craig

[george romano]

Re: too humid to paint?

I shot base/clear urethane in my driveway in July 2003 on my truck in muggy New England. No problems.

George

[John M.]

Re: too humid to paint?

The real issue with moisture problems in painting is not the level of moisture in the ambient air, but the level of moisture in the airstream exiting from the spray gun. You can damn near paint in the rain, if the compresed air is dry enough! I have a refrigerated dryer that then flows to a dessicant dryer, which will usually dry the airstream to better than -40 degrees F dewpoint. A cheap desicant dryer from the paint store will work well, but will have limited life with moist air going into it. I only use a refrigerated dryer to extend the time between regenerations on the dessicant dryer since I paint almost every day. A refrigerated dryer by itself will only dry the air to about +35 drgrees F, it is the dessicant that really pulls the moisture out of the air.

Regards, John McGraw

[Tracy C.]

Towanda *NM*

[terry leeker]

Re: too humid to paint?

John, as always is quite correct on the moisture issue. The critical factor is how much moisture is introduced in tho the air/paint stream. With high ambient humidity, one gets a double whammy - moisture in the atomized air/paint stream and little or no evaporation of the moisture droplets in the air/paint mixture as it approaches the surface to be painted. Living in Houston and having painted cars (in my home's three car garage) with urethane and polyuethane PPG products, I was forced to address this issue. What I came up with was a simple, inexpensive refigerant seperator. Take 50 feet of 3/8inch copper tubing, adapt to a short piece of hose to your compress, take the coil and set it in your deep sink (home made box with plastic or what ever you got),open the coil up so it looks like a big spring, run the copper bitter end out the lowest point, seal the penetration point, fill sink with water and a lot of ice, attach your standard water seperator at the low point outside of the cool tank and crack the drain valve. Voila! My '58 took $16 worth of ice for about four hours of painting. FYI A typical water seperator only works when the water vapor can be condensed (cooled) by the differental presure drop across the filter below the dewpoint. When the ambient air is much above 70 deg plus the added heat from compression process, the outlet air temp from the compressor is probably over 120deg. The standard seperator will be ineffective and the moisture will drop out in you hose as it cools or during the pressure drop/cooling when you pull the trigger on the paint gun.

[Chuck S.]

Re: too humid to paint?

Rick, there is no point in guessing about these kind of questions...Go right to the source: PPG Technical Service, 440-572-6111...you pay for the call, but the advice is free and they're happy to help.

By the way, it won't make any difference if you are painting in a booth; the air volume changes out so quickly that you are just using filtered ambient air. Dehumidifing is impossible to my knowledge. But, frankly, I don't know how you can spray a car without a booth; after a bit, you can't see the car for the fog. As alluded to earlier, your compressor MUST NOT BE IN THE SAME CLOSED SPACE in which you are painting. Those motors are not suitable for flammable vapor environments, plus I always wondered if a compressor could draw in a proper mixture of paint vapor and air to make it a simple diesel engine.

In summer, you may have to consider painting at night if that helps with lower temperature and humidity. I don't know if you are using the DCC urethane or the OMNI brand urethane, but I could begin to sense imminent difficulty ahead at around 85 degrees with DCC. Be sure you are working on the lower end of your reducer temperature range...by now you are probably using DT895 anyway. Humidity is seldom a problem out here unless it's pouring rain...and that seldom happens.