Keep a slab level with Great Stuff?

Last spring, after I jacked up my 3x6 oil barrel slab I posted asking about how to pump concrete under it to keep it where it is now.
Someone mentioned a grout pump & I've been watching for a good deal on one all summer- but no joy. My plans to build one have gone through lots of permutations- but when I saw the psi that commercial grout pumps operate at [several hundred psi], I decided to try some other thoughts.
Yesterday I thought I'd make a long nozzle for some masonry caulk and pump that in with a caulk gun- maybe I could work buying a pneumatic caulk gun into the job.
But today, when trying to decide what caulk was more likely to expand than shrink- I thought of Great Stuff.
The only thing Dow warns against when using outside is exposure to sunlight.
I calculate the weight at; 36x72x4" slab- 900 pounds 275gallons oil- 2100 pounds Barrel- 300 pounds snow 7 ice 300 pounds
total- 3600 pounds. area- 2592 square inches-
So even if I only managed 50% coverage, we're talking about less than a 3psi load. The Pro stuff is rated at nearly 20psi.
I'm not trying to raise the slab- just fill the 1/2-3/4 inch gap created when I leveled it.
I think I'm going to give it a shot unless someone has tried it with disastrous results. It is certainly both the cheapest and easiest idea I've come up with so far. A few cans of Great stuff and some extra tubing to get to the center of the slab.
Any thoughts?
Jim
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IMO, it can work. There may be some compression over time though. Foam insulation is used under concrete slabs all the time.
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wrote:

That may work. On the other hand, a 3x6 slab dont sound like it's worth all the hassle to buy a grout pump and all of that. Thats only 18 sq. ft. of concrete, which is about 1/4 yard of concrete. You could replace the thing with about 12 to 14 bags of ready-mix bagged concrete (just add water). (I am not sure how many bags are needed per sq. ft.) Or, if you have a few strong friends and some strong boards, just lift it, put fine gravel-sand under it, and set it back in place. But go ahead and try the great stuff and let us know if it works.
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You don't need a grout pump to use non shrink grout. Mix it a little thin and pour it down with a funnel.

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