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I am purchasing a 7' x 10' portable above-ground exercise pool which holds 2200 gallons of water. I plan to set it on my concrete patio which is quite wide and is 4" thick, with no rebar in it. Will the 4" concrete slab support 2200 gallons of water? My pool will be delivered soon so I need to know as soon as possible.

isherwood
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Cheryl Curran
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    Hello, and welcome to Stack Exchange. You added a good deal of information in response to @isherwood's excellent answer. It would be helpful if you edited that information back into your original question; that would make all this more useful for future readers. – Daniel Griscom Aug 19 '16 at 14:30

3 Answers3

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Concrete is usually rated at 3,000 or more PSI, which is a measure of crush resistance. You won't come anywhere near that. So the question becomes one of crack resistance, and that's going to depend almost entirely on the integrity of the substrate.

If it was poured directly on organic soil, it'll probably crack. If it's on a good base of gravel, sand, or recycled concrete, it'll probably hold well. Really, though, a crack won't change the slab's ability to support the pool. I'd assume that the pool will be placed on a mat of some sort that would protect it against any edges or irregularities in the concrete.

Some calculations (which are approximate, but close enough to allow us to dismiss outright crush strength as a concern):

7ft * 10ft = 70 sq ft
70 sq ft * 144 sq in = 10,080 sq in
17,458 lbs / 10,080 sq in = 1.7319 PSI

As you can see, crush resistance isn't a concern. It's all about whether the slab has to span any weak areas in the substrate, which could result in cracks and surface offset.

Ben Welborn
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isherwood
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  • The slab was pour under city permit. I will contact the prior owners who poured it to determine what is underneath, but I'm thinking it would be on a base of gravel, sand, etc., in order to meet code. We already have a hot tub on one end of the patio but it only holds 500 gals I think. Thank you so much for your answer. I appreciate it. – Cheryl Curran Aug 19 '16 at 13:32
  • Yes, there will be a mat under the pool to protect the bottom of the pool. Thanks, again. – Cheryl Curran Aug 19 '16 at 13:33
  • Considering that the depth of the tub and the pool will be similar, resulting in an expanded load distributed over a wider area, I'd expect that you won't have any problems. – isherwood Aug 19 '16 at 13:34
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    And welcome to SE. Please be aware that we're not a discussion forum, and that there is a protocol to be followed for Q&A resolution. Please see the Help pages if this comes as a surprise. :) – isherwood Aug 19 '16 at 13:35
  • If the pool has 2200 gallons of water x 8 lbs a gallon = 17,600 lbs, how much per sq. inch does that work out to be? – Cheryl Curran Aug 19 '16 at 13:39
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    There will be 4' of water and the dimensions are 7' x 10'. – Cheryl Curran Aug 19 '16 at 13:40
  • With the load distributed I would agree it would probably do fine.+ – Ed Beal Aug 19 '16 at 13:40
  • Where did you get 4'? I'd argue that, with the information given, my calculation is likely to be more accurate. It's moot anyway considering the range of expected values. – isherwood Aug 19 '16 at 14:44
  • Ah. Missed that in the pile. Apparently one of the other values is incorrect, then, or rounded severely. – isherwood Aug 19 '16 at 15:01
  • The manufacturer said it would have 54' high sides and the water would be able to come up to 48". – Cheryl Curran Aug 21 '16 at 13:13
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If your slab extends more than say 10" inches beyond the 7x10' perimeter, it'll most certainly will crack near the perimeter in time, probably crack even if it did have patio grade rebar job inside. I don't see how to mitigate that.

If it doesn't extend that far, and if it is on compacted earth or better, it may or may not crack underneath the pool depending on how uniformly compacted the base is, which could be mitigated to some extent by several layers of plywood with substantially overlapped seams.

2200 gallons = 294 cubic feet

294 cuft / 70 sqft = 4.2 feet deep

bill.withers
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What does the pool manufacturer say?

You could have the slab scored, or cut all the way through, into squares/rectangles with a cement saw. This would reduced likelyhood of the squares/rectangles cracking, but may lead to one or more square/rectangle settleing more than an adjoining rectangle, or lead to some tilting (even without the pool).

roger
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  • The entire slab is already scored or cut into several 10' x 10' squares. I was planning on putting it on one of those squares thinking that if it did crack it would limit the damage just to that square. So, this sounds like it will work. I also decided not to fill it to capacity, which should help as well. – Cheryl Curran Aug 22 '16 at 12:38