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Old 09-02-2018, 05:17 PM   #31
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Re: Rim joist insulation with 2" rigid pink foam


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Originally Posted by french_guy View Post
I would like to insulate my rim joist with 2" pink foam
I'm planning to proceed as follow
1) caulk the perimeter of the cavities
2) cut the pink foam to leave a gap all around (gap = size of the foam spray nozzle)
3) Put some caulk on the back of the piece of foam to make it stick to the rim joist, making sure I have my gap all around
4) Put spray foam insulation by inserting the nozzle of the can inside that gap

What do you think?
About the spray foam, should I use the regular Great Stuff, or the window foam that expand less?

Thanks
Hi:

I am doing the same project in my basement. First long piece of Pink FOam board, i used too much Great Stuff and it pushed out the pink board in some spots. So back to the starting board. My question....if I cut the foam board leaving only a smallish gap around all sides, does the caulking work best, like you did? Where I think I made an error was trying to fill the entire gap with Great Stuff (1.5" inches deep as I used 1.5" foam board) rather than just seal the gap. Hope that makes sense. So just wanted to see if when you caulked, you just sealed the outside gap, and didn't worry about getting caulking into the whole 1.5" gap area.

Thanks.
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Old 09-02-2018, 06:20 PM   #32
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Re: Rim joist insulation with 2" rigid pink foam


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Originally Posted by lem6611 View Post
Hi:

I am doing the same project in my basement. First long piece of Pink FOam board, i used too much Great Stuff and it pushed out the pink board in some spots. So back to the starting board. My question....if I cut the foam board leaving only a smallish gap around all sides, does the caulking work best, like you did? Where I think I made an error was trying to fill the entire gap with Great Stuff (1.5" inches deep as I used 1.5" foam board) rather than just seal the gap. Hope that makes sense. So just wanted to see if when you caulked, you just sealed the outside gap, and didn't worry about getting caulking into the whole 1.5" gap area.

Thanks.
Hi
I cut the foam as tight as I could, and just caulked the 4 sides....That's it
Didn't try to "push" the caulk deep inside
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Old 09-02-2018, 06:23 PM   #33
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Re: Rim joist insulation with 2" rigid pink foam


If you make the gap the width of the straw on the can you can reach all the way in and apply just a bead of foam. I use the gun that delivers a more controlled bead. The cans are kind of on or off.

Which type of can foam are you using, window and door, regular, or gaps and cracks. The last two expand a LOT. The low expansion window and door still expands but much less.

You can also apply a bead of caulking picture frame style before you insert the rigid. Then apply another bead before the next layer of foam or to finish it off.

Once you have played with the can foam you gain a better understanding about the mess it makes. Caulking is much more user friendly.

As a last resort there is a zero expanding foam, DAP. I don't consider it a rigid as the Great Stuff, but on 6" deep windows I like to foam it once and be done.

Bud
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Old 09-02-2018, 10:43 PM   #34
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Re: Rim joist insulation with 2" rigid pink foam


Thanks so much for the quick reply! You answered exactly the question I was trying to illustrate---if I needed to fill the entire gap with caulk. I did seal the inside of the "box" with caulk before I had inserted the pink foam board, so at least I did one thing right!

I appreciate again you taking the time to respond. Take care.
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Old 09-02-2018, 10:49 PM   #35
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Re: Rim joist insulation with 2" rigid pink foam


Hi Bud:

Thanks for the reply. I had used the regular Great Stuff expanding foam. It wasn't the type to fill big gaps, just the ordinary red can. I had cut the pink board 1/2 smaller the whole way around to provide enough gap, but like my first post said, I think my fatal mistake was pushing the foam all the way to the back and only stopped when it started to spill out of the front and sides. When I pulled off the foam board today, while there was a very nice seal on the top, what happened is about 1/4" down from the top at the back, foam got behind the pink board (remarkably, only about 3/16) and slightly pushed out the foam board, which allowed me to actually deflect the board and even broke the bead of Alex Plus caulking I put at the bottom. I was going to try and use 2 1/2" Grip Rite cap nails to nail the newly created hollow spot out, but worried that this could cause moisture problems that I'd never see once I frame out and drywall the walls.

Sounds like my best option when I re-cut the new pink board is to cut as tight as possible and then run a bead of Alex Plus caulking around the perimeter??

Thanks again Bud for your input and information. Take care.
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Old 09-02-2018, 10:55 PM   #36
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Re: Rim joist insulation with 2" rigid pink foam


Hi Bud. One last question....when you said "You can also apply a bead of caulking picture frame style before you insert the rigid. Then apply another bead before the next layer of foam or to finish it off." I was a bit unclear of the progression. I did apply originally the caulking around the inside perimeter of the joist rim box before putting the foam board in. After this, much like the French Guy did, I was not going to try and fill the gap completely with caulking or expanding foam, but just seal the exterior perimeter of the foam board. Would this be an acceptable option in lieu of filling the entire gap up with Great Stuff? I just wasn't sure when you mentioned about applying another bead of caulking before the next layer of foam. Hope this makes sense. Thanks for you insights!
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