New way to insulate slab?

[Jay430]

I'm getting ready to start on the foundation for my garage. And will be installing radiant heating into the floor. Here's where it gets interesting. My contractor has started using the spray type Corebond insulation under the slabs and says he'll never use the foam pads again if he can help it.
He said that 1 1/2" of the spray in will have an R rating of 10-12, and last for ever.
Has anyone here ever tried this? I'd hate to find out 2 or 3 years down the road that I have a problem.

Jay

 

[Backlight]

I've not tried, but out of interest what's the price difference? Why does he prefer spray over XPS?

 

[383]

How evenly can it be sprayed? One thing that causes floor cracks is variation in slab thickness.

 

[anthony666]

it works really good, seals up tight as a drum

 

[Jay430]

He told me that the main reasons he likes doing it is that when he has seen they foam board float, and when walking on it to lay out the pex and what ever else, that he has broken corners and edges off of the sheets. Also the R value will be 10-12.

To be honest, I haven't even priced out anything else but the price of spraying down 1 1/2" is $1 sq.ft. And he seems very confident that it will be more than level enough to pour over. The pad will be 4 1/2" minimum.

 

[ADSR]

Ive seen it done on this board a couple times.

 

[Twiggss]

The guy on here with the "harn" build did it and seemed to be pretty happy about it.

 

[The FIB]

Does spray foam have enough compressive strength to be used under a garage slab?

 

[kj_mustang]

Does spray foam have enough compressive strength to be used under a garage slab?

I have read figures of between 15- 25 psi but I don't know how accurate that is. The closed cell spray foam on my walls is pretty hard. I have pushed on it and it doesn't compress.

 

[mr overdunne]

Does spray foam have enough compressive strength to be used under a garage slab?

First thing I think of is great stuff. then again I'm not a civil engineer. Lol.

 

[theoldwizard1]

What is the cost difference between spray foam and and rigid foam.

 

[ADSR]

What is the cost difference between spray foam and and rigid foam.

I paid 15$ each for a 4x8x2 sheet r value 7.5. Thats 32 sq/ft.

 

[kj_mustang]

I paid 15$ each for a 4x8x2 sheet r value 7.5. Thats 32 sq/ft.

That must have been a long while ago or a very good deal. I see EPS or XPS 4'x8'x2" sheets for $25 - $30+.

 

[theoldwizard1]

Typical R value for foam is 5 per inch.

Your builder likes it because 1) he is lying about the R value of 1½" and 2) it is less labor to install and 3) who is actually going to check the thickness.

You want 2" of XPS sheet. It is also important that you run your foam down along the inside of the foundation to the frost line. No one realizes how much heat loss can go out the edge of the slab.

 

[anthony666]

my cost on 2"x2'x8' celfort eps is $20 a sheet .. that's a dollar and a quarter a foot .. add my time to re level the gravel and install everything, vapor barrier, box cutters & blades, tuck tape and a couple of cans of expanding foam, add a couple of helpers and a buck a foot looks like a killer deal

i get the purple stuff sprayed and i can walk on it safely next day .. the installer says you can walk on it sooner, but .....

everything is sealed up nice and tight, throw down some mesh and string the pex and it's miller time baby

 

[anthony666]

No one realizes how much heat loss can go out the edge of the slab.

my foam guy runs right up where the edge of the slab is, and feathers it into the wall cavity insulation .. i doubt it could possibly be tighter

 

[Highbeam]

First thing I think of is great stuff. then again I'm not a civil engineer. Lol.

I am a civil engineer and I also think of great stuff first. We know the PSI rating of EPS and XPS but the spray foam? Yikes.

 

[Fun pain]

what highbeam said!!!


and why pay more? $27.00 / 32sqft = $0.84 a sqft... so you would be paying 16% more to trust a contractor.......

(if all is well, and doesn't destroy the concrete floor)

If you have building codes/ inspections ask them (most say no)

 

[Nexussian]

I don't know what foam it was, but a friend that used to build houses swears by the spray in stuff under the slab.

He claims he had tried the various sheet products and the spray "beat" them all.

Unfortunately he's older, so getting details on "better how" is difficult.

He did say that his contractor could get an even layer (thickness) but that he had seen others have issues.

 

[4AudiQ]

Here is the Harn post:

http://www.garagejournal.com/forum/showthread.php?t=226535

 

[Fueler]

I'm a little confused in looking at the barn link. Shouldn't there be some rebar in the concrete? Seems like a lot of faith in the foam and the earth to stay put.

 

[rburke65]

And if the contractor had pieces of the foam board breaking off then his base must have been VERY uneven. Sounds like he is not into doing much grading.....