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marksto 04-18-2008 10:29 AM

Can foam sealer be used to seal the spaces in concrete block?
I have an old, small 800 sq ft concrete block home on 4 acres in the Tampa Bay area. It used to be the caretaker's home for a chicken farm on the property. Planning to live in it for a few years until we build a new home.

It is constructed from plain hollow block, no drywall, and there is no insulation in the cavities in the block. One westward-facing wall in particular gets a lot of sun and heat in the afternoon, and I considered having insulation installed in the block. Companies want $800-$1,000 and I hate to spend that much on a temporary home.

So, I was wondering if I could use canned foam insulation like Great Stuff to apply in each hollow wall cavity to provide better insulation at least on that one wall. I could drill small holes in the top and bottom of each vertical wall cavity line, squirt it at the bottom and allow any over-expansion to come out the top hole.

I've looked around and can't find any information on using this type of canned foam as insulation as opposed to something that just seals space. Not sure if this type of use would be appropriate and if the resulting insulative value would be worth the effort.

Any advice or information would be appreciated.

Termite 04-18-2008 10:44 AM

I guess it would serve your purposes, but you'll need lots of foam. Get the highly expansive stuff and plan on being at it a while. You'll likely need to install it in "lifts". Start at the bottom and build up from there. There are some better products than great stuff available that will be easier to use. They're sold as cartridge cans of foam that screw into an inexpensive foam gun with a metal nozzle. A good building supply center should have it. Not sure of the cost comparison to great stuff, but much easier to use, and it comes out of the nozzle a lot better.

There's a product called "icynene" (sp?) that is essentially the same thing. It is sprayed by insulators into a void and it expands to fill the void. Not a DIY thing though.

I don't know how much benefit you'll see from doing this. It certainly won't make it worse though!

Termite 04-18-2008 10:46 AM

Steer clear of electrical boxes and sources of heat, such as flues for stoves, furnaces, or water heaters. Spray foam is highly combustible.

If it gets into the electric boxes when it expands, just scrape as much of it as you can out of the inside of the box.

Maintenance 6 04-18-2008 12:27 PM

I highly doubt you'll be able to put it in one hole and have it expand over that distance. As termite said, you'll need to do it in several lifts. Another thing is that block cores don't necessarily line up vertically. You certainly will end up with voids that won't fill. One more problem, as I see it, is that concrete is very conductive. If you could fill all the voids, the webs in the block will continue to transfer heat/cold from inside to outside and vice versa. Covering the block with foam board will provide better results. You'd need to cover the foam board though. It's not safe to leave it exposed. If on the inside, cover it with drywall, or on the outside with siding.

concretemasonry 04-18-2008 01:18 PM

Filling the cores of a block wall, especially without commercial equipment is too costly to justify the cost. - Especially if you plan to live in it for a couple of years. It is just like trying to justfy great windows when you really cannot accurately measure the savings.

Rigid foam insulation is the only way to go for your situation, but that is not cheap. What do you plan to do with the house in a few years - sell it of level it?


kc5oh 04-18-2008 02:43 PM

That sounds like too much. I'm with concretemasonry on the rigid foam. If the house is that small you could use furring strips and panels.

And also, for the love of the FSM, do not use hardening foam if you do go that route.

marksto 04-21-2008 07:48 AM

Thanks very much for all the opinions and information. Rigid foam and the effort behind it is also a bit much, so I guess I'll just plan to make do with the hollow walls for now.

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