Humidity a concern?

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PostPosted: Wed Sep 28, 2022 10:20 pm
It’s been typically dry here and I have a good big moisture/ dirt filter but it’s supposed to be rainy the next 4 days and I’m ready to spray sealer and color coat on my car, is there any limit to the amount of humidity allowed for painting? I have a temporary spray booth, would it make sense to add heat? Another option is to wait until the weather returns to normal ( dry as Arizona) in 5 days. I could get a hygrometer. I did a search of this forum and saw one mention of a good job in 90% humidity. Thanks



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PostPosted: Wed Sep 28, 2022 11:03 pm
ive painted in the rain, well not actually IN the rain but in my booth with it raining outside. i do it all the time, it rains a lot here and the humidity is usually high. i really haven't seen or had any problems. one thing you might watch out for is condensation. it happens when you have drastic weather and or temperature changes. kinda like when you walk outside with that ice cold can of beer in your hand on a warm humid day, the moisture in the warm air condenses on the cold can. this can happen with metal items in your booth if they are cold and warm moist air reaches them.
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PostPosted: Thu Sep 29, 2022 9:12 am
Thanks Jay, that’s what I needed to know

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PostPosted: Thu Sep 29, 2022 9:34 pm
I love spraying in the rain. I have found that I get a lot less dust/garbage in my work (ok, play).

The only thing that I have found is I have to use an air blower if I am spraying the water based Envirobase.
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PostPosted: Fri Sep 30, 2022 9:46 am
From my research and limited experience:

Sealer: if its epoxy, high humidity should not effect the curing process but will effect how quickly the solvent will flash between coats. Either spray a single wet-coat, or wait longer (15 min for example) between coats.

Urethane: Humidity ACCELERATES the curing or 2X urethanes. If you are OK with an orange peel finish, then no worries. Just look out for condensate as others have mentioned, and you may have more condensate push through your gun's air nozzle as well (unless you have a really good means of cooling/capturing it).

This was most noticable for me when I sprayed my single-stage 2X semi-gloss black in my interior. Just couldn't avoid the orange peel when the humidity was near 100% in 80 deg weather.

When humidity is high, the acceleration of the cross-linking can occur before the solvents can evaporate, especially on the previous layer. You could experiment on using faster solvents and waiting longer between coats. Lighter coats help too.

In summary (for clearcoat-base), you can make it work but you won't have repeatable results from what you achieved in 40% RH. You will either need to just live with the orange peel (cut/buff), or experiment with technique and thinners to get the results you want.

If you are spraying flat clear for any reason, forget about it. It won't look right. The faster curing caused by high humidity won't get you that consistent flat finish.

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PostPosted: Fri Sep 30, 2022 10:15 am
Slow activators and reducers will eliminate the humidity issues with clear and single stage.
You can even by a Retarder (extremely slow reducer) that allows the clear to flow out and lay down.
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PostPosted: Fri Sep 30, 2022 2:08 pm
As a favour for a friend I paid for the paint and did the work on a hood for his Fiat Uno. The blue base coat went on beautifully well, and the clear flowed on looking like a glistening lake LOL

Then darn, there was a real cloudiness to the clear. I put it down to humidity. I was so pissed off I just left it outside for a few days before I could face looking at it again.

After a few days baking in the sun the cloudiness disappeared and the friend was very happy with the free paintwork and quality of it. Phew.



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PostPosted: Fri Sep 30, 2022 2:49 pm
@Coronet Well there ya go! glad someone with more experienced chimed-in, and I am glad I wasn't too far off. Sounds like you just need to experiment off the car with retarders, reducers, and activators in your sample humidity to get it right. Try contacting the supplier. I am sure their lab folks have somewhere to start from. Speedokote has always been very helpful to me when I ran into chemistry or application issues.

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PostPosted: Fri Sep 30, 2022 4:43 pm
Follow the tech sheet for the amount of reducer and/or retarder.
The key to using slower reducers is to allow each coat to flash off before spraying the next one.

You can usually see the vapors flashing off, if you look down the panel. Any moist looking spots are still flashing.

The other test is to touch the clear (usually on a the masking tape) and see if it strings when you pull your finger away. If so wait a bit longer. It's okay to see your fingerprint but you don't want it to see strings when you pull away.

Getting in a hurry increases your risks of runs and trapping solvents.
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PostPosted: Fri Sep 30, 2022 6:47 pm
100%. My first attempt was awash with runs. I have gotten past that hurdle (run-free), but struggling with the orange-peel. I'll get there! great tips on checking the clear on the masking tape.
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