GG curing and vapor barrier paint

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GG curing and vapor barrier paint

Postby chconnor » Tue Aug 24, 2010 8:54 pm

Hi - any reason to worry about painting a vapor barrier paint over a GG wall, in terms of curing? What if it's an internal partition wall, so that both sides (which both have GG layers) will have this paint on it? (might have some leftover paint, otherwise wouldn't use it...)

Searched around in the forums and couldn't find anything relevant... so, sorry if I've missed something...

Thanks,
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Re: GG curing and vapor barrier paint

Postby Eric.Desart » Tue Aug 24, 2010 9:44 pm

By definition providing both sides with a vapor barrier has no sense whatsoever.
Do you understand the difference between watertight and/or repellent paint and a vapor barrier?

I should say making both sides with a vapor barrier is wrong and senseless with or without GG. You can only hope that this vapor barrier at least partly fails otherwise can be the cause of moisture problems rather than be a solution to prevent them.

If both sides have comparable inside climate (can vary somewhat) on both sides just use standard paint allowing your wall to breath somewhat.

You only use a one sided vapor barrier when there is a clear longterm balance of dominant vapor transport in 1 direction.
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Re: GG curing and vapor barrier paint

Postby chconnor » Thu Aug 26, 2010 11:25 pm

Thanks, yeah, I realize there's no reason to do it; the only reason I was considering it was because I'll have some leftover vapor barrier paint ("vapor barrier", perm rating < 1 for the exterior walls, as required by code). I can buy separate, normal primer for the partition wall; I was just curious if using the vapor barrier paint would be bad for the GG curing (or bad for some other reasons, as you described.)

These are two residential rooms in a small outbuilding with a GG partition between them, same heat source/climate/moisture pattern, so as "same" as normal residential rooms could be. Sounds like you're saying that both sides with vapor barrier paint is potentially going to cause problems... Ok. Thanks for the feedback,

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Re: GG curing and vapor barrier paint

Postby chconnor » Fri Aug 27, 2010 7:03 pm

Hmmm... the local paint store guy (Kelly Moore) said that a lot of local contractors prime the entire inside of their projects with vapor barrier paint: partition walls, ceilings, exterior walls, etc. Not sure what this guy knows, or how intelligent of a practice that is, etc, but interesting to hear...

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Re: GG curing and vapor barrier paint

Postby Scott R. Foster » Sat Aug 28, 2010 12:21 am

interesting - why not ask him why
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Re: GG curing and vapor barrier paint

Postby chconnor » Sat Aug 28, 2010 1:01 am

Scott R. Foster wrote:interesting - why not ask him why


The impression I got from him was that here in the Pacific NW, where the general idea is to wage war against moisture against all odds or reason, builders just seal everything they can seal, but I'll probe him a little more next time I go in...
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Re: GG curing and vapor barrier paint

Postby Scott R. Foster » Sat Aug 28, 2010 2:01 am

ahh a general mold fighting step... cover everything with a waterproof layer... sorta
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Re: GG curing and vapor barrier paint

Postby Eric.Desart » Sat Aug 28, 2010 8:11 am

I asked:
Eric.Desart wrote:Do you understand the difference between watertight and/or repellent paint and a vapor barrier?

You didn't answer this, and the following posts suggest that you don't, then why not ask? (with watertight I meant waterproof)

And I said:
Eric.Desart wrote:You only use a one sided vapor barrier when there is a clear longterm balance of dominant vapor transport in 1 direction.

I don't think you understand this sentence either, so why not ask?
Physics works the same in the whole world.

Scott R. Foster wrote:ahh a general mold fighting step... cover everything with a waterproof layer... sorta

There is huge and principle difference between a vapor barrier and waterproof. Water is a liquid and vapor is a gas with a different molecular structure.

If you just paint anything on both sides which is a perfect vapor barrier you cause mold problems, not fight or solve them.
A typical transparent or colored varnish to protect wooden window frames is waterproof but NOT a vapor barrier. That way the wood can further dry out but protect the wood from water penetration.
Even roofing (that black stuff on roofs) is waterproof but NOT a perfect vapor barrier. If not, a lot of roofs should just rot.

Maybe in the US other laws of nature apply, but I never found that confirmed in any physics book.
Just the interpretation chconnor how you tell the words of the supplier shows that you or he doesn't understand the physical background of these words. Whether the supplier was that superficial about it or not I don't know. Nowhere a definition is given about, or relationship with hygrothermal conditions. This are just a collection of words.

Using generally perfect vapor barriers just for safety precaution, without understanding the when and why is the best manner to cause mold problems. And not seeing the difference between a vapor barrier and waterproof doesn't help either.

chconnor, if your inner rooms have comparable climate conditions (averaged over longer period, not on an hourly base), and that paint is indeed some kind of perfect vapor barrier, it can only cause risk, not solve or prevent a thing. That's how nature works all over the globe.
Due to difference in vapor tension (powerful force) on a short term, vapor will enter that wall, at moment x from one direction, at moment y from the other direction depending on the exact conditions at that particular moment (you hardly can make any construction vaporproof, gaps, edges, whatever). That moist will accumulate (depending on hygrothermal circumstances) and you prevent that wall to breath (evaporate) normally to get rid of that moist.
I can wash my raincoat a million times without problems. If I put that same raincoat moisty in a vaperproof bag, after some months it falls apart by rotting (I had the real live proof of that phenomenon).

To give an example: that was the problem in the 70ties when the first double glazing came on the market as a result of the energy crisis. One had not (yet) the later means and process quality experience to guarantee the edge gluing to be perfect vapor tight, causing moist to accumulate between the window panes (for some windows, not all of course).

A vapor barrier is also a matter of degree. Aluminum foil is almost a perfect vapor barrier, a thin plastic foil is a less good vapor barrier, while both are perfect waterproof. Which is why alu foil is that much integrated in food packaging (that's not mainly meant for the nice silver glancing), tobacco, cigarettes, vapor barrier on isolation blankets and so on.

Sometimes (or often) I don't know the perfect applying English word, but you should get the picture.
:twisted: For the time and price of these posts you could have bought some standard paint already and leave that vapor barrier paint on the shelf or please someone else with it who has a physical correct use for it.
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Re: GG curing and vapor barrier paint

Postby chconnor » Sat Aug 28, 2010 7:24 pm

Hi Eric, thanks for the info --

Eric.Desart wrote:I asked:
Eric.Desart wrote:Do you understand the difference between watertight and/or repellent paint and a vapor barrier?

You didn't answer this, and the following posts suggest that you don't, then why not ask? (with watertight I meant waterproof)

Sorry, I must not be writing very clearly; I thought I did, and think I do, understand the difference... this is why I answered:
chconnor wrote:("vapor barrier", perm rating < 1 for the exterior walls, as required by code)
...meaning that I was talking about a vapor barrier paint, not a waterproof paint, which I thought was the question you were getting at. This is why I asked the question about GG in the beginning, since I was worried about the vapor barrier impeding the curing of the GG.

Eric.Desart wrote:And I said:
Eric.Desart wrote:You only use a one sided vapor barrier when there is a clear longterm balance of dominant vapor transport in 1 direction.

I don't think you understand this sentence either, so why not ask?


Again, unless I'm fooling myself, I thought I did, and I think I do, understand your point. I think maybe we're miscommunicating a little? -- I already decided not to use the vapor barrier paint, because of your first post. I just posted the words of the paint store guy because I was surprised to hear him say it, and thought it might be interesting that apparently contractors around here (Bellingham, WA) are covering everything in vapor barrier paint (at least according to the paint store guy). I'm not trying to argue that covering my walls in vapor-proof paint is a good idea, or that these local builders know better. I'm sure it's similar to builders thinking they know how to improve sound isolation. :-)

Eric.Desart wrote:Using generally perfect vapor barriers just for safety precaution, without understanding the when and why is the best manner to cause mold problems.


Yeah, my friends in eco-building have made this point to me a lot of times; I mistakenly thought (until you posted) that it might not matter on an interior partition wall, since there wouldn't be a great difference in temperature or humidity between rooms, but you explained that temporary differences would be enough to cause problems, so that cleared that up for me, and I didn't feel the need to ask any more questions.

So, thanks. :-)

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Re: GG curing and vapor barrier paint

Postby Eric.Desart » Sat Aug 28, 2010 8:03 pm

chconnor,

It's OK, you're welcome.

If I misunderstood, I'm sorry. It gave me, as I understand now, wrongly the impression that your discussion with the local store guy and the further posts here, brought the whole thing back into doubt.

I misinterpreted the situation then.

Kind regards
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Re: GG curing and vapor barrier paint

Postby Ido » Mon Aug 30, 2010 11:43 am

that's real interesting, Eric.
I recently heard that soft plastic food containers, like for mayonaise, eventualy let some air molecules pass through them, which also influences their expiring date.
some such mayo plastic containers activley let air through the cap seals, when you squeeze, you hear and feel it,
it's intentional. knowing nothing of such things, I was really surprised.
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