# Attaching rigid foam to concrete



## Windows on Wash (Aug 30, 2011)

Are you going to be framing up the basement for finishing (i.e. wood framing inside of the foam wall)?

Concrete screws with washers will work, but most guys rely on chemical (i.e. glue) adhesion as a primary and the mechanical (i.e. nails and screws) as a temporary hold. 

If you are framing the wall right after the foam, you can just stick them up with the glue (be sure to use foam compliant) and shim between the framed wall and foam to hold the foam tight as the glue sets.


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## joecaption (Nov 30, 2011)

http://www.demandproducts.com/EIFS-items/item.php?l2=3,11,22&sku=GROUPCONGRIP
You do know foam can not be left exposed, right?
Cap nails are not long enough and would just bend when they hit the concrete.


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## VitoB (Nov 30, 2012)

Windows on Wash said:


> Are you going to be framing up the basement for finishing (i.e. wood framing inside of the foam wall)?
> 
> Concrete screws with washers will work, but most guys rely on chemical (i.e. glue) adhesion as a primary and the mechanical (i.e. nails and screws) as a temporary hold.
> 
> If you are framing the wall right after the foam, you can just stick them up with the glue (be sure to use foam compliant) and shim between the framed wall and foam to hold the foam tight as the glue sets.


Yes I will be framing a wall in front of the foam. I am not ready for the framing just yet, just trying to put up the foam for the insulation value at the moment. 



joecaption said:


> http://www.demandproducts.com/EIFS-items/item.php?l2=3,11,22&sku=GROUPCONGRIP
> You do know foam can not be left exposed, right?
> Cap nails are not long enough and would just bend when they hit the concrete.


Yes I understand if it catches fire it releases toxic fumes and I cannot leave it exposed.


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## concrete_joe (Oct 6, 2014)

more info on whats being done will help yield some answers. what are you planning to do with the walls?

depending on what the walls are, whats behind them, and ability to snake wires, i might suggest a few furring strips on angles 1st.


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## VitoB (Nov 30, 2012)

concrete_joe said:


> more info on whats being done will help yield some answers. what are you planning to do with the walls?
> 
> depending on what the walls are, whats behind them, and ability to snake wires, i might suggest a few furring strips on angles 1st.


I will be framing a 2x4 wall in front of my foam board.


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## concrete_joe (Oct 6, 2014)

do the walls have water infiltration issue, always damp, etc ?????

i might use some vertical furring 1st (add two pcs to wall between framed studs), then spot glue foam board to furring, etc. seal edges of foam board to studs to seal it good. or, furr wall (not horizontal furring), foam board the whole thing taping the seams, frame up to foam board. guess it depends on if that extra 1" or so is critical to the space needs, etc......

this allows air pockets on wall. there will always be moisture moving through the wall, etc. kinda same idea as insulating roof line, you need pocket of air to keep things good, etc.


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## VitoB (Nov 30, 2012)

concrete_joe said:


> do the walls have water infiltration issue, always damp, etc ?????
> 
> i might use some vertical furring 1st (add two pcs to wall between framed studs), then spot glue foam board to furring, etc. seal edges of foam board to studs to seal it good. or, furr wall (not horizontal furring), foam board the whole thing taping the seams, frame up to foam board. guess it depends on if that extra 1" or so is critical to the space needs, etc......
> 
> this allows air pockets on wall. there will always be moisture moving through the wall, etc. kinda same idea as insulating roof line, you need pocket of air to keep things good, etc.


Walls are dry, no issues with moisture at all. I am installing 2" XPS foam which I believe does breathe to some extent.


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## concrete_joe (Oct 6, 2014)

VitoB said:


> Walls are dry, no issues with moisture at all. I am installing 2" XPS foam which I believe does breathe to some extent.


those walls are backfilled outside, or no? even with outside walls being coated you still get moisture moving in/out. i like to leave air pockets, makes the space feel better imho. 

all you really need to do is spot glue the foam, tape the seams, push studs up against the foam, ......... foam wont go anywhere, etc.

the PL glues wont need bracing, once it sticks it will stay sticky and hold long enough for you to frame up to it. are you worried the foam boards will bend back and fall off?? 

just make sure the glue you use doesnt melt the foam, etc.

not sure how you are framing, but i would secure the sill and top plate, and then add foam board in as you framed making sure the foam board seams can be taped later, etc. thus skipping this whole need for glue, etc.


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## VitoB (Nov 30, 2012)

concrete_joe said:


> those walls are backfilled outside, or no? even with outside walls being coated you still get moisture moving in/out. i like to leave air pockets, makes the space feel better imho.
> 
> all you really need to do is spot glue the foam, tape the seams, push studs up against the foam, ......... foam wont go anywhere, etc.
> 
> ...


I installed the first few pieces by using spray foam to secure the foam to the concrete wall. I am looking for a better method.

I used a small bead of spray foam as well in the seams and then added some sheathing tape for an extra layer of protection.

The PL300 says it's made specifically for foam boards.

My foundation wall isn't perfectly flat, so part of the foam boards will not make complete contact. Is that OK?


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## Windows on Wash (Aug 30, 2011)

That is fine. You can cinch up the foam to block contact with the shims once you frame out the walls. 

Be sure that you seal all the gaps so that no conditioned air is getting behind the foam in the end.


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## VitoB (Nov 30, 2012)

Windows on Wash said:


> That is fine. You can cinch up the foam to block contact with the shims once you frame out the walls.
> 
> Be sure that you seal all the gaps so that no conditioned air is getting behind the foam in the end.


Do you mean shim up the 2x4s so they push up tight on the foam?

I am using spray foam before I join the pieces together at the joints.


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## concrete_joe (Oct 6, 2014)

VitoB said:


> Do you mean shim up the 2x4s so they push up tight on the foam?
> 
> I am using spray foam before I join the pieces together at the joints.


foam it, frame it, any lose areas wedge some shims behind 2x4 to hold foam tight, etc.

i say skip the foam... just dap a few spots, stick to wall, frame it, push 2x4's tight against the foam, pull trigger on air nailer, etc.


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## Windows on Wash (Aug 30, 2011)

Glue up the foam. If you are having issues with initial contact and hold, put some screws or nails in it. 

When you frame up the wall (unlikely that the foundation wall is plumb or straight) you will have some small gaps between the framing and the foam. Put shims (wedges) in those locations to hold the foam tight.


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## Gary in WA (Mar 11, 2009)

This is where two layers of 1" foam board will work better when going for 2". The foam board requires FULL CONTACT as said, glue grid pattern; *no air spaces*; http://joneakes.com/jons-fixit-database/743

Be sure to add foil tape or fiberglass tape/furnace mastic on seams, canned foam/caulking under it against slab for an air seal. Caulking beads under/over foam strips between bottom plate/slab. Do the wood rims with foiled foam board first (unless ext. FB already), much easier than after wall is built.

Gary


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## nap (Dec 4, 2007)

Gary in WA said:


> This is where two layers of 1" foam board will work better when going for 2". The foam board requires FULL CONTACT as said, glue grid pattern; *no air spaces*; http://joneakes.com/jons-fixit-database/743
> 
> Be sure to add foil tape or fiberglass tape/furnace mastic on seams, canned foam/caulking under it against slab for an air seal. Caulking beads under/over foam strips between bottom plate/slab. Do the wood rims with foiled foam board first (unless ext. FB already), much easier than after wall is built.
> 
> Gary


I don't read that as necessarily requiring full contact. What is critical is that there is no open space to allow airflow. That is the point of the cross grid pattern. 


In other words, the board is sealed against the wall although there will likely be some space behind it, even if caused due to the thickness of the glue itself (that is why no spot applications) . I suspect they are even concerned about convective currents between the top and bottom of the board within the sealed space so breaking that up into smaller increments would likely be critical to their instruction of using a grid pattern. 

just my untrained guess though.


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## Gary in WA (Mar 11, 2009)

The whole purpose of rigid foam board is to air seal, insulate/raise the warm side (condensing surface) temperature to prevent condensation, and allow any water capillarity from outside through concrete wall to slow to a crawl (permeability) going through it while basement heating system can handle it effectively. 

With any air gap; the moisture condenses on the (cold) concrete surface (rather than going through FB, then too warm to condense as now on other side of insulation), forms liquid water and gravity pools to your (hopefully) air tight glue bead or you may see water on the slab there. There would be no resistance at all to water with the gap -- unlike the XPS with a cellular structure (1.1 perms per inch; 2" = 0.55 perms) to let little through over time; http://www.foamular.com/foam/faqs/

Gary


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## concrete_joe (Oct 6, 2014)

there will always be space between wall and foam board, the wall is not perfectly flat and the foam will not have a glue that makes a perfect seal against the wall.

you dont need an air gap to have water condense on wall surface. with tight foam board you trap the moisture which is not good.

furred wall will allow an air pocket to allow moisture to move more freely and evaporate (be absorbed) into the pocket air and migrate out.

i also recommend laying down some powdered bug killer behind foam board on floor.... keeps the crawlers to a minimum.


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## nap (Dec 4, 2007)

concrete_joe said:


> there will always be space between wall and foam board, the wall is not perfectly flat and the foam will not have a glue that makes a perfect seal against the wall.
> 
> you dont need an air gap to have water condense on wall surface. with tight foam board you trap the moisture which is not good.
> 
> ...


I don't know what sort of adhesive you are considering but that is the purpose of applying the adhesive in a grid pattern. The adhesive provides an air proof cavity within the boundaries of the square of each grid section. It will prevent air flow that way which is the intent. Using a proper adhesive, you will create an airtight seal between the wall and the insulation board. 

with an open space the article states you will get convection flow from the bottom to the top and reverse. Due to the temp differences, especially if any of the wall is exposed outside, it will cause condensation to settle which is going to accumulate at the bottom plate and rot it. 

allowing airflow such that you allow the moisture to escape defeats the purpose of the insulation altogether. You are slowing the speed of the air movement due to the restriction of the materials but you are not preventing it.

If you have enough moisture you need to provide for evaporation you need to seal the wall or install a drain system outside of the wall before even getting this far.


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## concrete_joe (Oct 6, 2014)

if you create cavities with the glue then the cold surface of wall may condense water in that space,,,,,,, so from there where does that water go?? to avoid moisture problems you should allow airflow, etc.


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## nap (Dec 4, 2007)

concrete_joe said:


> if you create cavities with the glue then the cold surface of wall may condense water in that space,,,,,,, so from there where does that water go?? to avoid moisture problems you should allow airflow, etc.


that is why the grid. The temperature differential in a foot or so is not going to be great enough to cause evaporation and then condensation. 

allowing airflow defeats the purpose of the insulation since the only place for the air to flow would be into the room. That would mean you are allowing conditioned air to be exposed directly to the concrete wall.


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## concrete_joe (Oct 6, 2014)

moisture in air will migrate, you dont need "air flow" in terms of open ends, etc. some heat from inside will move towards the cold wall, just a tad slower because of the R value being added. that heat + air space will allow the moisture to absorb into the air pocket..... moisture can then migrate out.

with furring you'll have some open end pockets above the wall, just simply place some unfoiled fiberglass insulation across those open ends, this will allow the "air-flow", etc.

there will always be airflow, just slower when you add R value, etc.


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## Gary in WA (Mar 11, 2009)

The whole idea of foam board is to stop condensation on the cold concrete wall. It moves the FIRST condensing surface to the inside of foamboard BUT if the inside face is warm enough; it won't condense. ANY air space results in a cold concrete surface; moisture inbound (during heating season) through the wall from the earth will condense if the wall is at/below the condensing temperature. Without an air space, the foam is partially cold/partially warm (from the interior- which is why you don't want most of the R-value in the form of cavity fill), read this and note Fig. #3 and #4; http://www.buildingscience.com/docu...ld-weather-condensation-using-insulation/view

Foam board will be saturated from the earth (through the concrete) for most of winter, you don't want an air gap between the two for liquid water to collect; pp.11-14; 
http://aceee.org/files/proceedings/2006/data/papers/SS06_Panel1_Paper27.pdf

*Figs. 5, 7 *and *pp. 7 and 11*; http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CEkQFjAA&url=http%3A%2F%2Fwww.buildingscience.com%2Fdocuments%2Fbareports%2Fba-0202-basement-insulation-systems%2Fat_download%2Ffile&ei=xWiZUqLCJYjyoATO7YGoAQ&usg=AFQjCNGYl3LafAv-Hjm7Gq3ToLZQruI9mg&bvm=bv.57155469,d.cGU&cad=rja

Gary
PS. The air gap will be at concrete wall temps (not room air temps if 1' grid pattern) due to proximity and all the insulation is inboard. Granted, full contact is hard to do, hence using 2 layers of 1" on rough walls.


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