Replies

1. Expert Member
   MALCOLM TAYLOR | Mar 19, 2019 10:42am | #1

   They don't effectively air-seal. If you use sill-seal you need a bead of something at the concrete/wood intersection.

2. 
   PAUL KUENN | Mar 19, 2019 11:47am | #2

   We use acoustical caulk. Super sticky and messy and many mentions of it on GBA. Anyone ever test how long it takes to dry? 20 years? 100?

1. Expert Member
   BILL WICHERS | Mar 19, 2019 02:26pm | #5

   I think it’s intended to NOT dry. I know it’s still just as nasty years later as the day it went in though. I’ve had to clean many a tool after dealing with the stuff. It does do a really good job maintaining a seal on things that move a little though!

3. Expert Member
   RICHARD EVANS | Mar 19, 2019 12:34pm | #3

   Steve,

   I personally believe that either option is fine. I opted for the cheaper Owens Corning style material with Acoustical Sealant above and below it and achieved a very tight enclosure. More importantly, I also taped the sheathing to our ICF foundation. (If it was concrete, then I would have used liquid flash.) I believe this step (exterior air-sealing) is more critical as I have seen 5/8" thick gaps between mudsills and concrete that no rubber gasket would fill.

   It may sound like a lot, but I think it is worth taking the extra steps to air seal this part of the house (and area around trusses) as failing to do so can magnify heat loss due to the stack effect.

   To echo Paul's point, acoustical sealant is a real pleasure to work with! :-)

4. 
   Peter Yost | Mar 19, 2019 01:17pm | #4

   Hi Steve -

   I don't think that the evenness of the top of the foundation and the uneven point-loading of the mud sill (e.g. how compressed the sill sealer is at j-bolts compared to between) mean reliable air sealing from the sill sealer alone. Hence this product review (albeit dated) by Martin Holladay: https://www.greenbuildingadvisor.com/article/product-review-worlds-best-sill-seal.

   Note in this blog the comments; some good perspective and a detail from Michael Chandler, one of the original GreenBuildingAdvisors.

   Peter

5. 
   airfix | Mar 19, 2019 02:27pm | #6

   Great info again. I'm not excited about using acoustic caulk and the potential mess every time someone touches it at each stage of the construction.

   I've seen the product in the link that Peter presented before and Michael Chandlers comments seem to ring true about cost and grad school ideas. His detail of wrapping poly under the sill plate and over the top plate looks good but then I'm dealing with more tape to maintain the seal. Not sure I understand how the top plate wrap of poly over the sheathing helps with sealing.

   Bottom line is if I go with the Owens Corning sill sealer I need to have a backup plan. Perhaps using the acoustic sealant. If I go with the much more expensive EDPM gasket I probably don't need a backup plan?

   Steve

1. Expert Member
   MALCOLM TAYLOR | Mar 19, 2019 03:25pm | #7

   Steve,

   In past discussions here, when objections to using acoustical sealant came up, a more benign alternative was suggested: Pro Clima HF.

   https://www.greenbuildingadvisor.com/question/budget-friendly-alternative-to-pro-clima-contega-hf

6. 
   airfix | Mar 19, 2019 04:47pm | #8

   I just found these two useful links. One of which is a "back yard" test on the foam vs the EPDM gasket. While the back yard testing is not totally applicable as most sill seals are not exposed to UV and it doesn't really address sealing it is a side by side look at the materials.

   https://www.justneedspaint.com/house-gasket-durability/

   https://www.justneedspaint.com/an-airtight-home-how-to-choose-and-install-sill-sealer-gasket/

1. Expert Member
   MALCOLM TAYLOR | Mar 19, 2019 07:00pm | #9

   Steve,

   I don't think there is any doubt the gasket is a better product than sill-seal, but those backyard tests did nothing to prove that. Interior sill-seals are completely enclosed within the conditioned space, and those on exterior walls are pretty close to being too. Leaving scraps out on your lawn to test them is like leaving fibreglass batts or plywood in the same conditions. It just makes no sense.

7. 
   airfix | Mar 26, 2019 12:36am | #10

   Discussing this with my general he suggested that we use the Owens Corning sill seal but only install it under about 3" of the 2x6 sill plate. He suggested using a can of spray foam to foam the underside of the sill plate before it is bolted down and bolted down the foam has a chance to fully cure.

   Does anybody have any comments on this?

1. Expert Member
   MALCOLM TAYLOR | Mar 26, 2019 11:25am | #11

   It sounds like reinventing the wheel. Why not either use a gasket, or use sill -seal and run bead of sealant on either the interior or exterior of the joint between the sill and the foundation. That's how people generally do it.