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Is there any reason not to use vast amounts of Great Stuff foam?


Skoorb's Avatar
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10-29-10, 03:23 PM   #1  
Is there any reason not to use vast amounts of Great Stuff foam?

I'm looking at my joist bays again that I mostly did a year back. I have used 2" XPS but the sill plate is still totally exposed and in some cases kind of tricky to get to. Instead of putting more 2" foam in place and foaming around it I was thinking of doing a few "coats" of great stuff foam. I know that when too much of it is applied at once it tends to shrink back early on in the curing, so I was going to run a few "beads" of it no more than an inch or so thick. This would be cheaper than $300 for a two-part spray from, say, tigerfoam.com. Are there any problems with this approach?

GS foam is a closed-cell foam. There is also the "big gap" fill, but I imagine its R is even lower and perhaps it's not as strong.

 
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10-29-10, 08:00 PM   #2  
It can be done but does the cost out wat the time savings for the tiger foam

 
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10-30-10, 04:47 AM   #3  
Posted By: airman.1994 It can be done but does the cost out wat the time savings for the tiger foam
It really would be cheaper, I just don't have enough to make a $300 dual unit worth it.

So is Great Stuff effectively up to snuff with, say, Dow Frothpak in quality once it's cured, same lifespan, robustness, etc.?

 
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10-30-10, 05:20 AM   #4  
Just one additional thought. If you patch in all of the larger places, leaving reasonably sized gaps that will make caulking very easy, you will eliminate most of the volume required from the can foam. Detailed cut to fit is very labor intensive and actually can leave small gaps that aren't accessible to fill with foam. Leaving a .25 to .5" gap makes cutting simple, tack it in place with a nail or hot glue, and then foam the gaps.

Can foam is designed to yield a bead and makes for a poor replacement for spray on products.

Bud

 
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10-30-10, 05:45 AM   #5  
Posted By: Bud9051 Just one additional thought. If you patch in all of the larger places, leaving reasonably sized gaps that will make caulking very easy, you will eliminate most of the volume required from the can foam. Detailed cut to fit is very labor intensive and actually can leave small gaps that aren't accessible to fill with foam. Leaving a .25 to .5" gap makes cutting simple, tack it in place with a nail or hot glue, and then foam the gaps.

Can foam is designed to yield a bead and makes for a poor replacement for spray on products.

Bud
That's the approach I took with all of the joist bays, but at the time I wasn't bothering with the sill plate and now the beaded edges everywhere else are a bit of a hassle to get at except with some spray product.

I see that handi-foam sells $30-50 two-part systems but impossible to get without paying a lot in shipping (like $50!). Assuming great stuff is similar to handi-foam, handi says something like 3.5-5 R per inch in their one-component (i.e. simple can) foam and 6 in their regular two-component systems.

BTW here is a typical bay. I guess in retrospect I should have thrown a chunk of 2" on the sill. I guess I still could, bit of a pain, though. I'm tired of these joist bays


Can anyone think of a reason to not seal these sill plates up? They are sitting on a foam sill gasket and if I foam the top they'll be less likely to get wet from condensation but also far less able to dry out should they need to...

 
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10-30-10, 08:57 AM   #6  
If you look at the big picture, all of the heat loss issues around your house, there has to be a more productive place for your foam ($) and efforts, I'm smiling. Seriously, if I were to run the heat loss calculations for those exposed wood surfaces, it might be something like $3 per year (guessing). What I would do is leave it as is and wait for every time I have a partial can of foam with no place to finish it off.

I also have a house where I considered spray foam for some deep rim cavities, two foot overhang on two 26' walls. But I opted for mineral wool to replace the fiberglass that was there because I was concerned about spraying into a cavity. ie, having everything blow back at me. I'd love to practice, but not on this one.

Bud

 
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10-30-10, 10:32 AM   #7  
Posted By: Bud9051 If you look at the big picture, all of the heat loss issues around your house, there has to be a more productive place for your foam ($) and efforts, I'm smiling. Seriously, if I were to run the heat loss calculations for those exposed wood surfaces, it might be something like $3 per year (guessing). What I would do is leave it as is and wait for every time I have a partial can of foam with no place to finish it off.

I also have a house where I considered spray foam for some deep rim cavities, two foot overhang on two 26' walls. But I opted for mineral wool to replace the fiberglass that was there because I was concerned about spraying into a cavity. ie, having everything blow back at me. I'd love to practice, but not on this one.

Bud
Thanks--I guess the issue is I'm going to drywall it over soon and it will be hidden for eternity. I'm positive the real money lost here is negligible--I'd never make it back after spending it on foam. However, I'm concerned only about it being so poorly insulated through that piece of wood that it could cause condensation issue. That's the only reason I'd cover it to begin with, since it's resting on a cold block wall. It's been perfectly fine like this for the last 5 years but it's also been not closed in behind drywall

 
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11-02-10, 03:36 PM   #8  
Quick update, I finally found somewhere that sells handi-foam in small amounts without being reamed on shipping. Have not ordered yet, though. fasttoolnow Also found some on sprayfoamdirect to order singles.

Think I'll do this and top up my joist bays in any case, it's a higher R than great stuff.


Last edited by Skoorb; 11-02-10 at 04:04 PM.
 
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11-19-10, 06:53 AM   #9  
Skoorb,
I did just as you mentioned, and built (3 versions actually) of
a gun to attach to the can of foam to make it spray. Just for those
pesky tite spots you show.

In talking to the Dow people (they got kinda irritated at what I had done...)
the "great stuff" is only approved for 4 sq. inches of exposure
for the fire rating (don't quote me on the numbers).

But the fire rating is not as good as the 2 part, so they need
to keep the amount exposed down.

Note they call it a "sealant".

 
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11-19-10, 07:24 AM   #10  
Posted By: digger doug Skoorb,
I did just as you mentioned, and built (3 versions actually) of
a gun to attach to the can of foam to make it spray. Just for those
pesky tite spots you show.

In talking to the Dow people (they got kinda irritated at what I had done...)
the "great stuff" is only approved for 4 sq. inches of exposure
for the fire rating (don't quote me on the numbers).

But the fire rating is not as good as the 2 part, so they need
to keep the amount exposed down.

Note they call it a "sealant".
Glad the extension approach worked. I had to do it again this past weekend.

 
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11-29-10, 12:22 PM   #11  
Skoorb,

I didn't "extend" the nozzle with a tube. I added a second outer
nozzle and added compressed air to actually "throw" the material
and spray it. A little practice, I got pretty good coverage.

The one problem I had in that closed in area, was the compressed air would come
back at you (as wind), and the pattern was different from when I practiced it
out in the open on a flat board.

BUT as I said before, it's not proper to have much more than a "bead"
exposed, it's not made for the job.

 
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