Sealant for OSB Air Barrier
BrunoF
| Posted in General Questions on
I am looking for product recommendations for the sealant to use when making my OSB sheathing the primary air barrier.
I hope to get the crew to apply a bead of sealant to the top and bottom plates as well as corners before the sheathing goes up and I plan to then also seal from the inside once the house is framed.
If there are some specific products for this use please let me know.
Thx
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Replies
I like polyurethane sealants for this as they are readily available and very durable. Downsides are they are more expensive, and stinky while curing (but not too bad). These sealants stay stretchy and durable over time, and adhere strongly to pretty much everything, which helps them to ensure a good seal over time.
Bill
Bill, like OSI Quad?
Yep, that kind of stuff. I usually use the Loctite PL line products, but OSI Quad is essentially the same thing, and is from another reputable company. I'd have no problem using their product instead of the Loctite stuff I usually use.
Bill
I think Quad is a silane-modified polymer, not a PU, but I don't think that should bother you. If you have larger joints, Prosoco Joint & Seam Filler is, to me, a leader... it tools totally differently, dries differently... I'd grab a tube of that and maybe their Air Dam, which is similar to Quad.
Quad Max is silane modified polymer, but regular Quad is some other type of elastomer if I remember correctly.
BrunoF,
Contega HF often gets used as a more benign alternative to Tremco acoustical sealant.
I'll second Malcolm's suggestion of Contega HF. It's made specifically for this purpose and it's zero VOC. You do have to order it from foursevenfive.com but with a few days of planning ahead you won't have to worry.
If you're stuck using what's available at your lumberyard, I like Loctite's PL Premium; it sticks to things very well, especially if they're slightly damp. But it's very rigid when cured, which isn't ideal for an air-sealing product. Sashco's Big Stretch is also a good choice; it's very sticky and durable, and remains flexible.
Michael, VOC aside, is the Contega preferred to the Prosoco products?
Bruno, I don't have first-hand experience using Prosoco products but I know they are high quality and I'm sure they would be fine.
BrunoF,
One caution I would give to anyone in high seismic zones, is using a construction adhesive for air-sealing. It reduces the shear strength of walls.
I hadn’t considered that; thx! I’m in central NC so no factor for me.
> One caution I would give to anyone in high seismic zones, is using a construction adhesive for air-sealing. It reduces the shear strength of walls.
Had never thought about this before, so did some thinking and reading.
If I'm understanding this correctly, construction adhesive on a shear wall may actually increase its static shear load capacity, but decreases its ductility, which may actually make it more susceptible to cyclical loading induced by seismic events, despite the equivalent or higher static shear strength. Fair?
Patrick,
Yes that sounds fair. From what I understand It's the initial shock that seems to need a bit of elasticity in the shear walls, and the adhesive removes this. There is some interesting testing that showed that walls with an aggressive fastener schedule that are separated from the framing behind by foam (like Zip-R) can do really well in preventing the complete collapse of buildings - but their increased flexibility meant that short of collapse, the buildings sustained much more damage.
These are all theories I hope never to have to test.
> There is some interesting testing that showed that walls with an aggressive fastener schedule that are separated from the framing behind by foam (like Zip-R) can do really well in preventing the complete collapse of buildings - but their increased flexibility meant that short of collapse, the buildings sustained much more damage.
Truly fascinating. But it speaks to the ductility of nails, it would seem. It leads to another point which is that we typically think of buildings as either sound or unsound, not somewhere along a duty cycle. There's probably a lot of research in seismic construction that considers this, but I'm not familiar with it.
As far as the research you mentioned, if you have a link handy, I'd love to read more.
Unfortunately I read it from a link in a posting here in the Q&A about a year ago which I didn't save as I couldn't see the applicability to anything I do.
Seismic standards seem similar to other safety related requirements (like fire prevention and electrical services) in that they fall on a spectrum of possible responses and represent a balancing between the work and expense involved vs the potential to save lives.
All my residential projects now either follow the prescriptive path in our code, or if the design precludes that use an engineer. But I've also done a "post disaster" addition to our local fire-hall, which was more involved. I'm under no illusions that either type will survive given the right conditions. They just have a much better chance than many of the ones around them.
Note that Loctite's PL line includes things like "PL Premium", a construction adhesive, but also things like "PL Polyurethan Sealant, Window Door and Siding". "PL Premium sets up pretty hard, but not completely hard like Liquid Nails.
The PL line Polyurethane SEALANTS though, do NOT set up hard -- they set up to a very tough rubbery material a bit like a high-end rubber band. These are very different from the PL products intended for use as adhesives. I've had very good luck using the PL SEALANTS for air sealing, where they are basically like a very, very durable version of silicone. I would NOT use the PL ADHESIVES for air sealing purposes.
I think it's important to make the distinction here, since I think some in this thread might be mixing up the two products, which is easy to do since Loctite doesn't really make it easy to identify them seperately.
BTW, I like to use white sealants for air sealing. White tends to be less obtrusive if it oozes out somewhere visible most of the time, and it's easier to spot any places that you missed compared to using a clean sealant. I made the mistake of using some leftover "aluminum" color sealant once under a door sill, and that stuff oozed out and was a pain to clean up enough that it wasn't noticeable -- even a small amount of that silvery gray "aluminum" color looked weird, so it was necassary to do a really thorough job of cleaning it up, even though it was in a relatively hidden location.
Bill
I have done sealing OSB with caulks but it is a lot of work do it right. Even there, the adhesive can separate over time unless you install backer rod in joints which way more work.
Tapes are way easier and hold up better, I would not bother with caulk. This a good look at how tapes hold up on various surfaces:
https://www.finehomebuilding.com/project-guides/insulation/backyard-tape-test
https://www.finehomebuilding.com/2013/11/07/backyard-tape-test-10-months-later
Akos, I plan to do both; tape and sealant and lots of blocking between the attached garage to seal that as well.
Looks like I can get the Prosoco joint and seal filler locally and will have to order the Contega HF online. Both are the same price…I wonder which one would be better?
The joint and seam sets up harder than the contega. The Contega stays much stickier and more flexible.
Prosoco AirDam is more similar to Contega HF than the Joint & Seam Filler is. The datasheet says >800% elongation at break and that seems about right after I've messed around with some cured bits. I've only used it for window and door dams so far, but have seen lots of mentions of people using it as an air sealant between framing joints. Last time I bought some, it was a few bucks a sausage cheaper than Joint and Seam Filler in small quantities (I only bought 3 or 4 to try out).