# Weatherproofing - Great Stuff vs Caulk. Mold Issue.



## cjaustin81 (Sep 4, 2014)

I'm getting ready to insulate the wood rim joists in my basement and I wanted to know which product is the best to seal XPS foam and prevent mold. I recently finished a mold remediation in my basement and I need to make sure it doesn't return. 

The insulation I'm going to use for the rim joists is Owens Corning R10 XPS foam but I wasn't sure what would be the best mold free product to use to seal the foam to the foam (to create an air tight seal).

Would Great Stuff be better for this application? I assume I shouldn't use any glues to hold the XPS foam to the wood either.


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## ront02769 (Nov 28, 2008)

You could glue the foam in....but that would be extra work since you will NEVer get a perfect fit and have to great stuff it anyway. Great stuff will hold the foam in place and not generate mold.


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## cjaustin81 (Sep 4, 2014)

ront02769 said:


> You could glue the foam in....but that would be extra work since you will NEVer get a perfect fit and have to great stuff it anyway. Great stuff will hold the foam in place and not generate mold.


Thanks. I don't see any reason to use screws to hold the foam in place because I don't want any holes in the rim joist of the perimeter. I'm thinking that the Great Stuff will be enough to hold it in place and then I'll put some Roxul over it.


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## ron45 (Feb 25, 2014)

Just my opinion....
I would use fiberglass insulation. Easier to install, no caulk, fills all gaps, easy to replace should something go wrong.


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## Fix'n it (Mar 12, 2012)

you will not get a perfect fit with cut xps. but, unlesss your a hack, you can get very satisfactory results. and then caulk the seems. my whole house is done this way. when i first started, i tried spray foam. i wasn't happy with the results.


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## cjaustin81 (Sep 4, 2014)

Fix'n it said:


> you will not get a perfect fit with cut xps. but, unlesss your a hack, you can get very satisfactory results. and then caulk the seems. my whole house is done this way. when i first started, i tried spray foam. i wasn't happy with the results.


Are I saying you weren't happy w spray foam to
SEAL the XPS? Or using spray foam in place of XPS?

What were u not happy with?


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## 52Caddy (Jun 5, 2007)

I started gluing the foam board to the wall, but ended up just cutting them pretty close to size and tapping them into place. 
I put a small bead of greatstuff around the joints on the rim joist and then slide the foam board into place. Then I went around the edges of the foam board where it didn't match up just right and gave it another shot of greatstuff.
I think it worked out pretty good. I don't know what it is with that greatstuff, but I don't think I've ever been able to use it without getting some on my hands or someplace else I didn't want it, no matter how careful I am! And I use it a lot, damn woodpeckers...


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## cjaustin81 (Sep 4, 2014)

52Caddy said:


> I started gluing the foam board to the wall, but ended up just cutting them pretty close to size and tapping them into place.
> I put a small bead of greatstuff around the joints on the rim joist and then slide the foam board into place. Then I went around the edges of the foam board where it didn't match up just right and gave it another shot of greatstuff.
> I think it worked out pretty good. I don't know what it is with that greatstuff, but I don't think I've ever been able to use it without getting some on my hands or someplace else I didn't want it, no matter how careful I am! And I use it a lot, damn woodpeckers...


LOL, I was just talking to my mom and she indicated that has happened to my dad too. 

As far as not getting it everywhere, this is why I'm thinking about using the "Windows & Door" version of Great Stuff for this job. The Windows and Doors has lower pressure and a smaller stream (at least that's what I've been told). I would imagine the insulation values are the same. 

Once you get it on something you don't want, can't you just scrape it up? This is really my first time using this stuff myself.


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## Fix'n it (Mar 12, 2012)

cjaustin81 said:


> Are I saying you weren't happy w spray foam to
> SEAL the XPS? Or using spray foam in place of XPS?
> 
> What were u not happy with?


i cut the xps to fit tight. the SF just sat on top of that = i didn't like that.
i also tried spraying the corners with SF and then pushing the xps into place.
the foam would then push the xps out of the cavity = causing other problems.
and its a lot messyer and much more expensive. 

if you insist on using Sf and xps. cut the xps about 1/2" smaller all the way around. center it in place. the SF the gap. no benift to this, that i see, and perhapss problems.


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## 52Caddy (Jun 5, 2007)

Yeah, you can scrap it off most -not all- things pretty easy, other than cloths and hands! The hands are the most annoying part. It doesn't come off easily.
As for the windows and doors version, at least around here, costs quite a bit more. $3.42 for the regular and $5.34 for the doors and windows version, plus I think the doors version has less product. Just be careful with the regular stuff and save some money.


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## cjaustin81 (Sep 4, 2014)

When you cut the XPS smaller, do you stick the spray foam nozzle inside the small gap and let it expand?

Or do you just do the outside perimeter?


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## Fix'n it (Mar 12, 2012)

cjaustin81 said:


> When you cut the XPS smaller, do you stick the spray foam nozzle inside the small gap and let it expand?


that is what i would do. but i didn't use that method. i tight fit and caulked.


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## cjaustin81 (Sep 4, 2014)

Fix'n it said:


> that is what i would do. but i didn't use that method. i tight fit and caulked.


But my big issue with caulk is mildew and mold. I just had mold in my basement and live on a lake so there's a bit of moisture. If you top that with a couple cracks in the foundation (which I had professionally sealed), moisture is bound to come in. 

That's the only reason I'm looking at spray foam. 

However, after looking at the spray foam it appears to have a higher insulation value than calk but I believe that's a moot point. 

I would much rather use caulk, I'm just concerned that if I do it will develop mold/mildew on the surface but maybe it won't.


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## cjaustin81 (Sep 4, 2014)

Question, the rim joist cavity is 2" deep and I'm using 2" XPS. Should I put the foam and then spray foam? Or should I try to spray a small bit around the gaps of the wood first and the out the foam and spray more?

I want the foam to lay flat against the wood.


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## ront02769 (Nov 28, 2008)

I would squirt the great stuff around the rear perimeter of the bay and then shove the insulating foam in. Great stuff will hold it in place and seal the cracks.

Also the windows and doors great stuff is not lower pressure shooting from the can but lower pressure when it expands. Fill between window and studs with the original great stuff. And you have a good chance that your windows will not open and close nicely as the foam will actually bend the window sides in! Ron


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## RegeSullivan (Dec 8, 2006)

Keep a little acetone close by when using spray foam. Dampen a rag with it to clean the foam of your hands even after it cures. Works on gorilla glue also.


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## cjaustin81 (Sep 4, 2014)

ront02769 said:


> I would squirt the great stuff around the rear perimeter of the bay and then shove the insulating foam in. Great stuff will hold it in place and seal the cracks.
> 
> Also the windows and doors great stuff is not lower pressure shooting from the can but lower pressure when it expands. Fill between window and studs with the original great stuff. And you have a good chance that your windows will not open and close nicely as the foam will actually bend the window sides in! Ron


I heard it's thinner though when it sprays. I may need the gun to dial it in as thin as I can get it regardless of the version I get.

Might just use the regular stuff w the gun.


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## ront02769 (Nov 28, 2008)

You may be missing my point. The window and door stuff does not expand as much or with as much force as the regular and cures flexible instead of rock hard like the original. For doing your basement, you can use either and don't need the gun. Problem with the gun is that it is a PITA to clean AND requires a special cleaner. Spend ten bucks total and get a can of window and door and a can of original from Benny's or wherever. Try both and see what works best for you. If you put the great stuff around the perimeter first, you don't have to worry about getting into tiny cracks with the nozzle as it will bind to the foam board. Ron


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