Insulation in Core of Concrete Blocks

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Old 01-12-17, 10:00 AM
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Insulation in Core of Concrete Blocks

Wondering if any of you think this is a total waste of time and money. As I mentioned in my other post, I'll be insulating my rim joists. One portion of the cinder block basement wall below it is open at the top, probably 25 feet of it. Plan is to stuff something down the cavities primarily to give support to spray foam I'll use to close off the tops of the blocks' cores.

But then I was considering, while I have them open should I be putting polystyrene beads or maybe just shooting foam down them to get a insulation inside. I know the thermal bridging in a concrete block is atrocious. I'd imagine a block wall is probably 1/3 solid concrete and mortar and 2/3 is probably the hollow portions, so I know you will not get a lot of bang for the buck simply because the thermal bridging likely eliminates the majority of the benefit, at least that's my guess.

Half of the 1/3 of the 25' wall is only 4 feet tall, and I have no idea exactly how far down the beads will go on even the taller portions. Maybe mortar will stop them half way. Is this worth the time and trouble or just save it for bigger and better things and ways to insulate and seal? Could any of the things I've spoken of cause moisture issues, sealing the tops, etc.?
 
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Old 01-12-17, 11:53 AM
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Sealing the tops is fine and desirable. Adding insulation will probably not make a difference as the remaining thermal bridge you mentioned will conduct right past it. Stuffing them with fiberglass insulation to support the foam insulation is a good approach.

Note, can foam doesn't like cold temperatures.

Bud
 
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Old 01-12-17, 04:24 PM
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Long ago my parents built a hose with block basement walls. I remember helping pour vermiculite to fill the cavities in the block. Poly beads are probably more free flowing so you'll have less problems with voids though if you've ever opened up a bean bag chair you'll know that those beads can be a real mess especially if the humidity is low.
 
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Old 01-12-17, 05:12 PM
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Is this worth the time and trouble or just save it for bigger and better things and ways to insulate and seal?
Even if you could fill all the cavities you still have uninsulated areas so net gain is zip.

Alternative options will gain much more!
 
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Old 01-12-17, 06:27 PM
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Why not apply foam sheathing like "Thermax" to the interior surface of the block?
 
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Old 01-12-17, 07:25 PM
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I was pretty skeptical about the value of doing this, and I'd not in a million years consider it if the wall was already closed. But, since they aren't, I thought I should ask since this is my last change to do so.
Pilot Dane, did you think it helped in any way? Of course, that's difficult to tell I assume.
 
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Old 01-13-17, 06:22 AM
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Filling the blocks with some type of pour in insulation isn't a case of going from zero to some improved r-value, as an air cavity does provide resistance to heat flow, aka r-value. Roughly, your current cavities are about r-4 but the block webs are less than r-1. An 8" poured concrete wall has an r-value of about 1. The improvement from upgrading those cavities to r-8 would be so small the benefits would never pay for the materials let alone the effort. But, do seal them on top.

However, add just 1" of rigid (more would be better) on the inside of the wall areas that are exposed to the elements on the outside and then your results will be significant. Detail that rigid on top and air seal and your heating costs will be noticeably reduced and that basement area much warmer.

Bud
 
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Old 01-13-17, 11:51 AM
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Last question, hopefully. Since there is a gap between the bottom sill and the wall I'll be filling this with spray foam, Great Stuff. Should I be concerned about water moving up the wall through the spray foam into bottom sill? It currently sits, for the most part, on god knows what. There is definitely more of a connection on the outside of the wall to the bottom sill, but it looks like the gap was just filled with mortar or stucco. While being constructed, there are also what appear to have been broken bricks stuck in between the board and the wall in places. So, there's not too much of a connection right now, for better or worse.

If this were built today there would be something between the bottom sill and blocks to stop capillary action of moisture up the wall. I believe those thin foam strips is what was used fairly recently, but even this may be dated as far as I know. Obviously I cannot imagine using the foam strips between the spray foam and the board, but maybe there is a tape of some sort that can be used. Or, am I totally overthinking this and would the spray foam itself be sufficient to stop (or at least not allow) capillary action between the blocks and the bottom sill?

Either way, thank God they don't build them like they used to.
 
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Old 01-13-17, 01:55 PM
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I believe the Great Stuff is a closed cell foam so should no absorb moisture. Also, any moisture moving up through the wall would most likely dry to the outside.

Years ago they used metal flashing on top of concrete walls as a moisture and termite barrier. That may be an option, but I don't think it would be necessary. But it might help your OCD nature, I suffer from that as well .

Bud
 
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Old 01-13-17, 02:22 PM
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That's great to know. And you are correct on the OCD part. I just know I'll be thinking after the project about how many ways I could have done it better. Hey, it keeps us learning I suppose.
 
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Old 01-13-17, 02:36 PM
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Too bad about the OCD.

I have CDO - similar symptoms but the letters are in alphabetical order, as they should be.
 
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Old 01-13-17, 02:48 PM
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HA! Love it. I'll have to share that with a friend who has the real deal.
 
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Old 01-13-17, 02:57 PM
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One of the drawbacks for being obsessive and being a builder is you develop x-ray vision. Even when a shortcut is buried behind something you can still see it and it bothers you.

And you are correct about the learning part.

Bud
 
 

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