I am considering getting on of the DIY spray foam kits for a variety of small projects around my house (1921 1.5 Story Bungalow in Minneapolis).
One of the things I would use if for is to insulate my rim joist. However, every space between floor joists has been filled with cement above the foundation. It starts out about the thickness of the foundation and tapers to near zero at the top of the rim joist. Would foaming over the cement work OK, or do I really need to remove the cement to get efective air sealing and insulation?
Thanks,
Erik
Replies
Foaming over the cement will definitely work, in terms of improving energy efficiency. The danger would be that you would increase the propensity of the wood to rot, with the cement "pulling" moisture up from the foundation, and nowhere for it to escape. (I have no idea how great this danger would be.)
Lots of discussions here as to the purpose of that cement, with no sure resolution. It may be to anchor the joists (typically there's no sill plate below them in this setup), may be to air seal, may be to discourage rodents. May be all 3 and more.
I had not considered rot.
I was told by someone locally that it was done in that era becuse the lumber was not as dry back then, and the cement was to help keep the joist from warping/twisting as it dried after instalation, so I suppse we can ad that to the list of possibilites!
Thanks!