What is the best sealant to use for airsealing?
Ine
| Posted in PassivHaus on
I know I want seal as many air paths as possible. Is there one particular sealant that works best for things like drywall to studs, spaces between double studs, rigid foam to studs and PE film?
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Replies
For air sealing cracks that are too narrow for spray foam, choose a polyurethane caulk.
Between bottom plates and the subfloor, use an EPDM gasket.
To adhere rigid foam to studs, use a construction adhesive labeled for use with rigid foam (a foam-compatible adhesive).
Sealing polyethyelene sheeting seams is difficult. The time-honored sealant is Tremco acoutical sealant ("black death") between overlapped sheets of poly; the overlap must occur over a framing member so that fasteners or a subsequent layer of material provides pressure on the joint. Some contractors' tapes work with some types of poly, depending on the poly coating.
Martin, why do you prefer polyurethane caulk to siliconized acrylic for air sealing gypsum panels to studs? My understanding is that the latex part gives adhesion and the silicon part gives stretchability.
Also, from my reading, it seems that elastomeric polymer/resin-based caulks like OSI Quad and Quad Max are similar in features/performance to polyurethane caulks. Do you concur?
Thanks Martin, If I'm doing double stud walls, does the inner wall's bottom plate need a gasket as well as the outer one?
I had checked the Tremco's website and it says the acoustic sealant vapor is harmful and it also says the stuff never dries. Is this a problem in a tight house?
Donald,
At a minimum, your house needs a continuous, balloon-like air barrier surrounding the conditioned space -- one that you can draw on the plans without lifting your pen from the paper. In theory, that means you only have to seal under one of the bottom plates of your double walls, not both (you can choose either the inner or outer wall). However, redundant air barriers don't hurt.
I can't imagine that there will be significant outgassing from the Tremco acoustical sealant. Since the bead will be encapsulated by poly on both sides, there's little opportunity for evaporation. However, I'm an old carpenter who spent years breathing hot asphalt bubbling in a roofing kettle, and watching polyurethane finish curing on hardwood floors. When I was a kid, we melted lead scraps in old tin cans for fun. My brain cells may not all be there. I'm not particularly sensitive. If you or anyone in your family suffers from chemical sensitivity, you'll have to ask someone else -- not this old carpenter.
Martin,
I spent a number of years screenprinting. I know my brain cells aren't all there anymore and all those years of smelling fumes and washing my hands in xylol and toluene seem to have made more sensitive to organic vapors, not less, so I try to stay away from anything solvent based if I can.
Thanks again for your answers. This site is a great resource.
Where can a mere mortal (read - not contractor) buy the Tremco sealants? I am doing vapor barrier in my crawlspace and need to get something real sticky, since I don't want to rely just on seam tape.
Apollo,
Here is a link to a Q&A thread on the topic -- and the thread includes lots of suggestions and links for anyone interested in buying Tremco acoustical sealant: Good source for acoustical sealant?
Home Depot (and menards i think) carries OSI SC-170 and 175 in larger tubes - and it appears to be a comparable 'black goo' sealant for the same use.
I have used it in my home and offgasing wasnt' alarming in any fashion.
Builder used a comparable white version - still 'thick peanut butter gooey' 2+yrs later.
We used a lot of 3M 8067 flashing tape for air sealing at various locations, along with Tremco acoustical sealant. We put epdm gaskets under both inner and outer bottom plates as well as under the sill, where we also used Tremco sealant. We ended up with a tight house, .6ach 50. During the blower door test last week, we used the 3M tape and some spray foam to seal the few spots with obvious leaks.
We also used Siga tapes around the windows and to seal the Siga air barrier where needed. The tapes seal tenaciously, but are about twice the cost of the 3M tape.
We plan to use the Tremco stuff to seal the drywall to the plates.
Hi Martin,
My house has a polyethylene gasket between the mudsill and the top of the concrete slab. The house is 9 years old. The builder (i 2006) used a sealant to seal the gap between the top of the concrete slab and the foam gasket and between the foam gasket and the bottom of the sill plate. Last week I noticed that in some areas there is a gap between the sill plate and the foam gasket as shown in this link ( https://plus.google.com/u/0/wm/4/photos/108320462450148241817/albums/6112474261116999073?authkey=CPDJn9Tq4_jbggE ). I got cold air coming to the house. Can I use Tremco acoustic sealant to seal this gap? I want to seal this gap first and apply siga wigluv air sealing tape to air seal the mudsill area. This will provide me with two layers for protection.
Naty,
I would be more likely to use a high-quality caulk (perhaps a polyurethane caulk) in this location rather than acoustical sealant.
Thanks Martin for your quick response. I wasn't sure if polyurethane caulk adhered to the polyethylene foam gasket. Now I know it works. Do you have any caulk brand that you would recommend? In our local Homedepot, I saw Loctite PL Gray Polyurethane Window, Door & Siding Sealant. Is this good enough for this job? I also saw Sonolastic NP1 online.