# Out door concrete slab for hot tub



## catfish1 (Jun 26, 2010)

I live in northwestern CT and want to pour a 9'x9' concrete slab for a hot tub, do I need footing below the frost line?, or just 6-8" crushed stone and re-bar enforced 6" slab. Any help would be greatly apreciated Thank Eric


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## jomama45 (Nov 13, 2008)

I generally drill & pour 4-5 sono tubes under the pad to play it safe. Frost shouldn't get too deep under a hot-tub, as they do loose some heat & help protect the ground under them from frost. If you're sure that the ground is hard enough, you can probably get away with just the gravel base and slab on grade. If concerned yet, you could probably put some rigid foam on the ground around the perimeter of the slab for a little extra protection.


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## stadry (Jun 20, 2009)

in northern ny ( binghamton ), we placed ours on 6" crushed stone, 6" pad of conc, & 2" of foam,,, typical frost depth was 4' but only everywhere else,,, under the tub it never got below 50f ( left a remote thermometer under the tub ) :thumbsup:


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## Knucklez (Oct 21, 2007)

i never hear people talk about the ground grid that is supposed to be installed under the tub. any help on this issue?

does your tub sit no the 2" of foam? if so, maybe the cement is NOT warmed by the tub and so frost could be a real concern? 

i would be leery of putting sonotubes under a slab. the slab which is NOT directly over the sonotubes could be forced up due to the frost heave, but the slab that IS over the sonotube (and tied in with rebar) would not move. this will crack the slab. i would rather have the slab floating (over crushed stone etc.) so that it all moves together.

Knucklez


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## Scuba_Dave (Jan 16, 2009)

My last house the tub sat on a dug out area that I filled with concrete rubble, about 12" deep
Then I poured 2-3" of cement over it just for a level surface
Never moved in 5-6 years

This house the 1st tub is ona slab that is anywhere from 8-20" thick
Also partially filled with rubble....hasn't moved in 6 years

My 2nd tub was simply installed over levelled concrete pavers 4-6" deep
These were maybe 24" square
Its been there 3 years now


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