Specialty vs. standard caulks for air sealing gaps
I am about to start the process of air sealing a stick-built/OSB-sheathed home. My plan is to either use tapes or caulks to seal along “the usual” leaky points (plate/wall junctions, sheathing panel joints, around penetrations, etc.).
I can’t help but notice the massive price difference for specialty products such as Prosoco’s Joint and Seam Filler (north of $23/20 oz tube) vs. a ‘conventional’ caulk– for comparison, OSI Quad (closer to $12/20 oz). Multiplied over an entire house, this ends up being a significant difference.
Having not used any of the specialty sealants, perhaps there is something I’m missing. I can’t imagine a decent quality exterior grade flexible caulk (OSI quad, for example) not doing a dang good job of blocking air flow.
Anyone with experience using normal caulks/sealants for air sealing?
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Most of the concern is about longevity of the caulk seal. I have myself seen silicone separate years later and obviously once that happens, you lose your seal. I’ve also seen some silicone that’s been ok for a decade or more, which makes me suspect it’s a bit like paint and depends a lot on surface prep.
I’ve heard stories about canned foam turning to dust over the years, but I’ve only ever personally seen that where the foam is exposed to sunlight where it most certainly DOES degrade. When indoors or covered, it seems to last. Other products that are supposedly sun-proof like duct seal (the tar-like sealing clay) dries out after maybe 10-20 years and needs to be replaced.
Urethane caulks are generally thought to be superior for long-term outdoor sealing, but I’m not sure if they’ve been around long enough for anyone to know for sure how they compare. “Stretchy” caulks (big stretch, etc) are likely to hold up better where you expect some movement from thermal cycling or settling, but the other issues remain. Surface prep likely affects all types of sealants.
Bill
Definitely do some shopping around. I bought 2 cases of Tremco Acoustical sealant for my house that worked out to be $12 a tube for the 32oz quart tubes after shipping. I still have 5 or 6 tubes left over after the house has all been sealed up and the first blower door test completed. I did spend a fair amount on a lot of zip tape but coming in with the first blower door test well below 1.0 air exchanges made up for it.
Trying to caulk you way to a tight house in the long run is asking for trouble. Trying to make it air and liquid tight is even harder. Speaking from personal experience, It is a lot of linear feet and no matter how good your intention, you'll get sloppy and end up with caulk separating. For most caulk to work, you need to put backer rod behind, gets VERY annoying quick.
Stick with tape, provided you roll it, it is much harder to mess up.
If you are looking for a belts and suspenders approach, than by all means buy the cheapest flex caulk you can buy, just as long as you tape afterward. I've had good luck with green glue SEALANT (not the compound) but use it mostly for interior sealing. Because it is water based, clean up is much easier than standard acoustical sealant.
I've used Tremco's Dymonic 100 for sealing gaps in the sheathing, foundation to sheathing joint, and around windows. It's fairly easy to use if the temperature is above 60°F, just need to make sure that not only the gap get's filled up with the sealant, but also an 1" or so on each side of the gap. You can get 20 oz sausages for about $9 a piece. Prosoco can be applied to wet surfaces and in the rain and I think that's what makes it more expensive.
Two notes about caulking – first, I agree with Akos that tape seems to be more robust than caulk, if you have decent surface prep, ie, the surfaces are clean. Second, like other mechanical joints and intersections of shapes, the shape and proportions of the joint make a large difference in the joint stresses. The depth and curvature of the caulked joint are important. This may mean that backer rod is required…I think this is what Akos was getting at.
Did you see Fine Homebuilding's article on this?
https://www.finehomebuilding.com/2004/05/01/making-sense-of-caulks-and-sealants
I read it, and then didn't follow it's advice. LOL.
Poly spray foam is nasty stuff but I've found it's far easier to seal up (and insulate) cracks than construction tapes or pure (non-water) silicone.
Maybe I just can't tape well. (Interestingly, people "ding" caulk for needing a clean surface. I'm my DIY experience, tapes need an even _cleaner_ surface than caulks.)
Jp
I appreciate everyone's replies.
I am going to take a hybrid approach, and I did find some 'reasonable' priced products.
Tremco's Dymonic can be purchased locally for $8/20 oz. sausage tube, and I have seen it explicitly endorsed (Matt Risinger) as exterior air sealant. I talked with a couple of folks about it and it sounds like a really good product -- very sticky, flexible after curing, and a good price point. I plan to use this as my "go-to" sealant: Rim-joists, sheathing panel butt-joints, around penetrations, etc. With backer rock where necessary.
I also found Tescon Vana tape from 475 Building Supply at around $38 per 30 meter roll. I'll use this where caulk looks more challenging or the gaps are big. I did get their primer as well. I plan to use this on the exterior, to seal the bottom edge of the OSB to the concrete stem wall. I like that this will also protect the underside of the OSB from any splashed-up water.
I found this excerpt on sealants and the use of backer rod from Hammer and Hand's Best Practices Manual to be a helpful guide: https://hammerandhand.com/best-practices/manual/2-sealant-joints/2-1-sealant-joint-design/
Our goal was a Passive House level of air sealing, so I used mostly the Tescon Vana tape, along with their Profil and Extoseal Encors tapes. I was especially impressed with the Tescon Vana as long as you have a dry substrate. 475HPBS also has a liquid membrane available now that can be applied by spraying or with a brush. And the HF Sealant, although expensive, is pretty tenacious stuff, sticking to just about anything.
Late in our build I was able to try out the Prosoco R-Guard series of products: Joint and Seam, Fast Flash, and Air Dam. I was extremely happy with all three. Hammer and Hand have YouTube videos showing their use of these products. They've been time-tested in the commercial building world, so they should hold up well.
The one big advantage the tapes enjoy over the liquid membranes is that they can be applied in colder weather. Apart from that, I found the liquid membranes to be easier to apply, and more idiot proof (although they can get pretty messy if you're not careful). As already pointed out, the Prosoco products can be used even when the substrate is damp, which can be a big help in keeping things moving along.
I would also recommend using the Roflex EPDM gaskets from 475HPBS for any pipe penetrations through your air barrier --- makes air sealing these areas very straightforward.
For our heat pump we used a PVC pipe as a counduit to hold the lineset, packing the voids in the PVC with bits of Rockwool before sealing up the ends with duct seal. The duct seal is holding up well.
Using the Roflex gaskets, or using PVC pipe as a conduit for a series of pipes-lines-wires in conjunction with the Roflex gaskets, means that any future repairs or maintenance should be more straightforward. The pipes are free to move in or out since only the outside edges of the Roflex are taped/sealed to the sheathing. Properly sized, the opening in the center of the Roflex gasket has only a friction fit around the pipe itself. Especially helpful when the heat pumps need to be changed out, or a frost-free hose bib needs to be replaced, and you're trying to avoid any damage to a carefully established air barrier.
If you're interested, I tried to detail all areas of air sealing on our blog with photos and explanations: http://www.kimchiandkraut.net
I really enjoyed the air sealing process, so hopefully you'll enjoy it as much as I did. Good luck with your project!