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Cut and Cobble with Damaged ICF Blocks

The recent severe weather in the Midwest (I'm in central Illinois, climate zone 5A) left me with A LOT of damaged ICF blocks that were intended to be used for my foundation walls. Most of it is unusable (without significant bracing) due to the "lego nubs" being broken off or large chunks from the corners missing or one side of the block is broken but the other side is just fine. (The wind picked up the bundles of blocks, broke them up, and blew the blocks across a corn field...I'm still picking up little bits of EPS).

So now I'm trying to come up with some way of RE-USING the EPS instead of just trashing/recycling it. I had two ideas churning in my head and I read Martin's blog about "Cut and Cobble" so I feel inspired to get some advice and/or ideas from others.

I have two ideas on how to use it. Both involve "disassembling" the blocks into two pieces of 4' long by 16" high by 2.75" thick pieces of EPS.

1.) The attic is planned to be ~R-60 with DIY blown cellulose. My idea is prior to blowing the cellulose, I would cut and cobble the EPS foam between the joists. I'm thinking that I wouldn't have to worry about sealing the seams, tight/loose fits, expansion/contraction of wood. The 16"+ of cellulose and airtight ceiling would take care of all that.
2.) Use the pieces of EPS as additional sub-slab insulation. Again, I feel that this is an area where the installation doesn't need to be "perfect" in order to still be effective.

Thoughts and advice are GREATLY appreciated!!!

- Rob

Asked by Robert Kohaus
Posted Tue, 12/03/2013 - 15:12


6 Answers

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I should add these are LOGIX ICF blocks. They have a compressive strength of 23.9 psi and a density of 1.72 pcf. R value is 4.13 per inch.

Answered by Robert Kohaus
Posted Tue, 12/03/2013 - 15:55

Helpful? 0

Sub-slab seems like a perfect application, and still an appropriate R-value for slab insulation in a central IL/zone 5a location with a 2.75" + 2.75" ICF wall. An big chunks taken off corners can be filled touched up with a bit of FrothPak or similar before pouring, but don't sweat the minor stuff.

Put the poly vapor barrier over the EPS rather than under it, or you'll have quite a bit of water in the voids & seams of the foam, which would mess up any finish-floor you might be looking to install in then next 2-3 years it would take for it to completely dry. With the poly over the EPS there won't be any voids to collect water seepage from the dripping saturated curing concrete, and only the excess moisture in the concrete after the cure needs to dry before the finish floor is put down.

Answered by Dana Dorsett
Posted Tue, 12/03/2013 - 17:14

Helpful? 0

I too noticed the appropriateness of the ~R-11 value of the foam for a sub-slab application. Given that the blocks are designed to contain concrete (albeit in a different orientation), I figure they'll probably work out pretty well.

I'm basically going to build an ICF wall....just in a single layer and laying on the ground. I'll use the same foam adhesive that I used when building the foundation walls between the blocks to hold them together and to fill any larger voids or missing chunks. Then put the poly vapor on top of the foam and have the flat work guys pour as they normally would.

Is the compressive strength and density high enough for this sub-slab application? I've read people use 15 psi foam, but it seems like the 25 psi (Type IX) is more common?

Answered by Robert Kohaus
Posted Tue, 12/03/2013 - 22:48

Helpful? 0

15 psi rated foam is PLENTY for a 3-4" slab, even if you were planning on parking a fully-armored hummer on it.

Foam adhesive doesn't have much R-value- it's fine for tacking the ICF blocks together, but use a bit of can-foam or FrothPak to fill in any missing corners or huge dents, etc. Where it expands proud of the EPS plane you can easily trim it flush with a flexible saw blade once the foam has cured for a day. (I use standard Asian cross cut hand saw for this type of trimming- they have narrow kerf flexible blades and cut on the pull rather than the push.)

Answered by Dana Dorsett
Posted Wed, 12/04/2013 - 16:02

Helpful? 0

I agree with Dana. It makes much more sense to use this material under your slab than in your attic.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 12/05/2013 - 06:05

Helpful? 0

Thanks guys. We'll see how it goes.

Answered by Robert Kohaus
Posted Thu, 12/05/2013 - 23:34

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