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Asher
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# Posted: 18 May 2016 03:43pm
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I am planning on using I-joist on our cabin, since this is a crawl space design I am wondering if I should paint the joist for a little added protection. The space should stay plenty dry but it wouldn't take much for me to spray them with my airless before setting in place.
What do you think?
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Eddy G
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# Posted: 18 May 2016 05:09pm - Edited by: Eddy G
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I don't believe "paint" is of any benefit under your cabin.
Unless the cabin sits over very moist soil or open water I don't think treatment of any kind is necessary.
Our cabin is on a slopped area and sits 12" to 30" off the ground. The earth is generally dry under there.
The original 1/2 of the cabin has been there since 1950 and an addition was put on in 1967...
That's give or take 50 to 75 years through some pretty harsh New England weather and the joists and floor boards are still solid as a rock....
That said, I'm not up on the newest and greatest wood preservatives. Maybe there's something out there.
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bldginsp
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# Posted: 18 May 2016 08:44pm
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Couldn't hurt I suppose. But if the I joists are in a situation where they are exposed to excessive moisture I doubt paint would prevent rot, maybe delay it. If you are at all concerned I think the best thing to do is either get them higher, or put in as much underfloor ventilation as you can, or both.
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Don_P
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# Posted: 18 May 2016 09:25pm
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Paint does a good job of repelling liquid water and keeping it from soaking into the wood but I don't know of any finish that can keep humidity, water vapor, out for long. If its a concern, put that money towards a 2" thick "rat slab" under there?
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Asher
Member
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# Posted: 18 May 2016 09:29pm
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There shouldn't be any moisture issue, I will have a very good drain system in place to keep water away... I just always have that "swollen particle board picture" in my head every time I look at the boards they use for the webbing...
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Don_P
Member
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# Posted: 18 May 2016 10:09pm
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I wonder if something like Thompsons might be better at saturating the porous surface with a breatheable finish that repels (beads) water rather than paints skin... I dunno. I do wish they would use Advantek in the webs.
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bldginsp
Member
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# Posted: 18 May 2016 10:21pm
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Asher- I agree that swollen OSB is ugly and scary, but it only happens when the stuff gets wet. I live in a dry climate, so I don't know what years of 99% humidity in the summers can do to it, but I doubt it will harm it.
I left a piece of OSB out in the rain and snow just to see what would happen, it looks pretty bad after 3-4 years. Problem is that the fibers are compressed during manufacture, then when it gets exposed to water the fibers swell up again, but when the water leaves the fibers don't shrink back to their compressed state, they stay swollen. When plywood gets wet it swells up a little, but when it dries it goes down to its original dimension, since it was never compressed. I don't like OSB, but maybe I'm just old school. But it's being used everywhere. Wonder what it's going to look like in 30 years when they reroof.
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toyota_mdt_tech
Member
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# Posted: 18 May 2016 11:03pm
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I'd get a sprayer and spray on Jasco wood preservative. Or one of those cheapo pump up week killer spray bottles. Nice little wand, go under there and spray it all. It will turn it green. No bugs will bother it. Or any brand of wood preservative. Home Depot sells "Copper Green" too
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Asher
Member
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# Posted: 19 May 2016 08:08am
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Thanks guys, I was thinking of doing a quick spray just before I set the joist in then maybe a quick touch up in the cut areas... That was my thought, to just add a little protection against bugs and resist any water mishap that might happed over the years...
I just wasn't sure if this was a "no-no" to paint the joist..
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bldginsp
Member
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# Posted: 19 May 2016 08:25am - Edited by: bldginsp
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Never heard of any manufacturer requirement prohibiting painting an I joist. But if they are high and dry I think its unnecessary.
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Don_P
Member
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# Posted: 19 May 2016 08:29am
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Google Flak jacket I joists and no burn coating, these are both intumescent paints that are applied to joists so I don't think there is any prohibition. The manufacturers help lines are usually quick to respond though.
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bldginsp
Member
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# Posted: 19 May 2016 12:47pm
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The first place you will see rot in any floor is around the perimeter, unless there is a plumbing leak inside. So painting or treating the ends of joists is not a bad idea.
I always try to treat the exposed ends of rafters since that's the first thing to go. I would NOT treat all the joists with preservative unless you are installing in a situation where the joists would be exposed to a lot of moisture. Sounds like you are not.
Rim joists and ends of joists on the perimeter won't rot if properly covered etc., but experience has shown that this, along with rafter tails, is the first thing that goes with time
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KinAlberta
Member
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# Posted: 23 May 2016 11:30am
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My lay opinion: I'd consider a paint coating for fire proofing or maybe a light stain to deter bugs.
Paint though might add and eventually trap moisture creating the problem you're trying to avoid.
Maybe lay a strip of flashing material along the top if there is any risk that water could reach it from leaky pipes or infiltration.
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Don_P
Member
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# Posted: 23 May 2016 09:19pm
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You'd lose the ability to glue the subfloor down, I don't think I'd want to give that up. The Flak Jacket joists are not sprayed on the top edge, so they do have an up/ down orientation.
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