Drying time needed for exterior latex paint before rain

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Old 04-24-06, 08:33 PM
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Drying time needed for exterior latex paint before rain

I'm branching out to exterior painting, and I'm concerned about painting when rain is expected within 24 hours. I operate in the Philadelphia, PA suburbs. We get a fair amount of rain in the spring. In the summer, we can go for weeks with afternoon and evening thundershowers expected every day. Most latex paints I use dry in about 4 hours. But, what happens if rain blows in after 5 or 6 or 8 hours??
 
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Old 04-25-06, 04:35 AM
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I'm out here in the ocean Wanna-Be, it's wacky out here for exteriors (which if you remember I'm working on one now)

I can be listening to the radio saying how sunny it is while I'm rushing to pack my stuff up in the rain-which happened last week
lol

Conventional Wisdom says if you've got 4-6 of good dry-time, you should be OK
The paint and humidity will affect this, as will the amount of rain and splash-back, and the vertical vs. horizontal surfaces etc...

What happens?
If it's OK, then nothing
If it's not quite dry enough, or it rains too hard too soon, the surface may look pretty bad
You may have to sand and repaint
 
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Old 04-25-06, 03:46 PM
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Thanks! 4-6 hours to dry sounds reasonable.

In an ideal world, it would be nice to have no rain for 24 hours after painting. My S-W rep (in his "ivory tower") recommends 24 hours. But, as I said, here in the real world of the Phila-PA burbs the threat of afternoon and evening thunderstorms during the summer is VERY common.
 
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Old 04-25-06, 03:54 PM
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Slickshift hit on a key word: humidity. That is the most important thing. I painted the trim on a cedar house up on pilings on the beach, 25 years ago, and did so just prior to the fog rolling in. I think there already was some fog in the air when I was painting and it just got worse and worse. The next day I returned to the house and all the trim I had painted the evening before was nowhere to be found. It erased. It didn't even run down on the silvery cedar siding and wreck it(luckily). It so thoroughly washed off it was as if I dreamed I had painted the trim. A very learning experience that was for me.

I will never ever again paint when I know the humidity level is high, and I feel the situation will then only get worse, instead of better.
 
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Old 04-25-06, 06:02 PM
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Originally Posted by DaVeBoy
Slickshift hit on a key word: humidity.
Yes, I always factor humidity into the drying time.
 
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Old 04-26-06, 03:47 PM
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Originally Posted by Wannabe-A-Pro
Most latex paints I use dry in about 4 hours. But, what happens if rain blows in after 5 or 6 or 8 hours??
Actually, I'd say the paint is quite dry already well before 4 hours...to the point you can't leave a finger mark in it. Once it gets to feel like it has totally skinned over, I don't think you have anything to worry about.

But let's say you paint and the humidity level is high, so after an hour it still feels wet to the touch? Time to go, "Uh-ohhhhhhh. I think I goofed!"
 
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Old 04-26-06, 06:17 PM
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Originally Posted by DaVeBoy
Actually, I'd say the paint is quite dry already well before 4 hours...to the point you can't leave a finger mark in it. Once it gets to feel like it has totally skinned over, I don't think you have anything to worry about.
Well, I should qualify my statement. Most latex paints I use are dry "to the touch" in 1-2 hours, maybe less. But, after 1-2 hours I would not want the paint subjected to a rainstorm. I would want a minimum of 4-6 hours before rain, preferably 8-12 hours to be safe. As I said, my S-W rep recommends 24 hours, but 24 hours is not realistic in my rainy locale.
 
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Old 04-28-06, 03:08 PM
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There are many many variables. Humidity is a big factor but don't forget what type of substrate, paint, method and thickness applied. And then you need to factor in sun and wind [or lack of]. Each job will be different. I have had jobs get rained on 1 hr after completion with no ill effects and have had jobs that dried for 8 hrs that required a lot of fixing.

All you can do is use your best judgement, hope for the best and play the cards you are dealt.
 
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Old 04-29-06, 12:18 PM
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Thanks Mark. Some times, you just gotta go for it!!
 
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Old 06-22-12, 08:20 PM
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Drying time needed for exterior paint ... Part 2:

Now what about the drying time of exterior primer before rain? Would that be the same 4 to 6 hours, or does primer have different requirements to be safe enough to be exposed to rain and other humidity?

In my case my project small and can be moved, but the end result will be having it outside year around.

MstrPBK
St. Paul, MN USA
 
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Old 06-22-12, 08:38 PM
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Welcome to the forums

Primer's not as durable as paint but I would think a light rain several hours later would pose little threat.

I paint outside but the garage is always empty if I think there's any chance of rain so I can get the project out of the rain while it's drying.
 
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Old 06-23-12, 04:54 AM
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There are many factors that determine the drying time of the primer. Different primers dry at different rates - read the label! Next weather conditions play a part. Primer/paint will dry quicker in hot dry weather, cool temps or high humidity can slow down the drying process. Wind can also speed up drying some. How dry/sealed the substrate is also plays a part - dry or porous substrate will suck up the primer quicker resulting in quicker drying time.

An hour or so after the primer is dry to the touch should be enough time for latex primer to fend off light rain. A hard rain will affect the primer if it's not good and dry. If the primer appears to be compromised - scuff sand and reprime

Oil base primer takes longer to dry but can withstand rain fairly soon. As long as the substrate is dry when the primer is applied - rain [but not a gully washer] won't effect it too much 30 minutes after it's applied. Rain will slow down the drying time and might affect the looks but shouldn't hurt it's bond with the substrate.

What are you painting? what coatings do you intend to use?
 
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