Can you put a pool on a 12-inches of sand playset site? Pool prep...

[KayDub23]

Hello all and TIA for your help...kind of a long story but Hubs just spent weeks hauling in sand and leveling a spot for our Intex Ultra XTR frame style pool. It looked perfect : ) then it rained : ( The back half of the cleared area pooled up with water pretty good and was very mushy. He added more sand to that side to level if off again but now we're worried that the pool will sink on that side and not sure what to do.

This part is the long story about what's under there...about 4 years ago we had professional landscapers bring up the level of our backyard about 3-5 feet and angle it all toward the left side of the yard because it was basically a mushy wetland. This involved bringing in fill, sand and then topsoil. At the same time they put in a playset area on the dry area (roughly middle) of the yard with about 12 inches of sand (I think) instead of the topsoil and then wood chips on top of that. Since it's the biggest, flattest part of the yard, Hubs moved out the playset, shoveled out the wood chips, and leveled the sand that was already there, adding more to make it higher (because we could see water pooling on the back half after taking out the wood chips), and more level.

He's tamped it down with a rented roller and measured it and it's super super level. We're just not sure how stable 18 inches of sand is? And if not, how to amend? French drain? Dig out sand and add crushed stone underneath? Thanks so much for any advice. We live in NH if that makes a difference.

 

[stringer77]

pics or it didn't happen

 

[KayDub23]

pics or it didn't happen

Your wish is my command

 

[JimR1998]

I am very much a newbie so take this as a grain of sand. I'm curious what others have to say here too.

18" of sand is not stable and I'd be worried that your base is washing out even before the pool is there. I've been in Intex style pools that were laid in a big sandbox but usually on a few inches of sand for level. 12-18" is a beach! Mixed in with wood chips I can only imagine how soft it must be, right at the bottom of a hill no less.

A lot of incorrect site prep was already done but I'd be inclined to salvage what's there, somehow. How big/deep is the pool? I'd consider using 2-1" layers of foam (taped) and try the pool on top of that. The foam basically spreads the load out evenly over the sand so it stays flat and undisturbed. But if groundwater is pushing UP or sand washing OUT then this will only get you so far. You may need a french drain to get the water out. A similar engineering technique using foam is done on a much bigger scale for building foundations.

Otherwise you might be in store for a dig out, lots of sand, soil, and chips, with trucked infill. $$$$

Good luck. Let us know what you decide.

 

[johnm160]

I would be inclined to put some kind of retaining wall ish type thing on the low end to help prevent washout.

 

[KayDub23]

Thanks for the responses. To clarify, what's in the "pool spot" right now...we removed the 6 inches of wood chips to reveal about 9 inches of compacted sand that have been in that spot (as part of the playset area) for about 4 years. So there are no wood chips mixed in there, it's just playground sand. Then we added about 3-4 inches of masonry sand on the low end up to 1/2 inch or less on the high end to level the area. The lower end is now feeling mushy after the rain, and if you walk on it you get about 1/8 inch footprint. I don't think we're worried about washout as much as the pool sinking on the lower end (but I haven't done a pool so maybe I should be worried about wash out, too).

I am interested in the idea of the foam pad...where does one get such a thing and is it cut to order or do you layer up pre-cut pieces?

 

[JoeSelf]

should be on undisturbed soil. sand will wash away. water weighs 8.6 lbs per gallon. posts will sink in sand.

 

[Mermaid Mama]

We put down foam board on top of a bunch of sand. It says in the XTR manual NOT to put the liner directly on top of sand or loose soil. We just put one together and I think this is bc our liner weighs 300 lbs so dragging that over sand and trying to get it in place would have made an absolute mess of it despite packing it down with a gas powered compacter. The sand gets dry and brittle the longer it's exposed. I read a tip about putting big pieces of cardboard on the bottoms of your feet while sand is down to avoid messing it up. Good luck!

 

[awhitese]

A raised bed of any sort will wash out. The best bed is to dig or hollow out the spot and backfill with your base. That will prevent washout. The first base I used was 3" stone dust. This was for a 10'x30" easy-up starter pool. According the the lawncare folks, that should be enough to prevent grass from growing up through. When we moved up to the frame pool, I remove the stone dust base and opted for play sand. Even when compacted, you could still leave foot prints int he sand under the filled pool. I removed that and switched to clay sand. When compacted, it is still 'soft' (ie., doesn't feel like walking on concrete) and you can't leave impressions in it. It is easy to re-level and adjust in the spring (if you have removed the pool for the winter).

P.S. The catch with clay sand is the small rocks that always seem to appear in it. You may need to screen the clay sand with laying down the final inch.

 

[Mermaid Mama]

We put down foam board on top of a bunch of sand. It says in the XTR manual NOT to put the liner directly on top of sand or loose soil. We just put one together and I think this is bc our liner weighs 300 lbs so dragging that over sand and trying to get it in place would have made an absolute mess of it despite packing it down with a gas powered compacter. The sand gets dry and brittle the longer it's exposed. I read a tip about putting big pieces of cardboard on the bottoms of your feet while sand is down to avoid messing it up. Good luck!

I thought this may help. Was told by one of the expert builders that cement sand was ok to put under foam board and won't wash out. This is my install thread. SWG & Gas heater that will work on temp & long term pool?

 

[JimR1998]

I am interested in the idea of the foam pad...where does one get such a thing and is it cut to order or do you layer up pre-cut pieces?

Extruded Polystyrene Foam, abbreviated as XPS Rigid Foam. It's available at Home Depot(Pink) and Lowes(Blue). It should be easy to find in NH. Costs about $20 for a 4x8 sheet 1" thick. Some people use anti-fatigue foam mats instead, but they will deform and I think rigid is best in your case. There are so many different types of sand, I don't think adding another type as an overlay will help.

Most people set their blocks on compacted soil/stone and cut the foam to fit around. In your case, you definitely do not want to set those blocks on sand because they will sink. The plastic foot by itself will cut into the foam. I think I read here that someone put a piece of tile under the foot (on top of the foam) so it doesn't cut in. Sounds reasonable.

 

[zea3]

I would lay layers of crusher or decomposed granite and compact that down. You don't use sand as a foundation for a pool no matter how well it is compacted. It will wash out and the legs will sink.

 

[awhitese]

I would lay layers of crusher or decomposed granite and compact that down. You don't use sand as a foundation for a pool no matter how well it is compacted. It will wash out and the legs will sink.

Decomposed granite produces radon. Just saying.

For the legs, I suggest 6"x12" patio blocks to avoid them sinking. Even under the metal walled pool I had when growing up, they put 12"x12" patio blocks (and that was 30+ years ago).

Any of the sands I have used have not washed out from under my pool. They cannot wash out. The sand is in a hole such that the top of the sand is even and flush with the soil/landscape surrounding it. If you build up from the surrounding area, then yes it would/will wash out.

 

[KayDub23]

We put down foam board on top of a bunch of sand. It says in the XTR manual NOT to put the liner directly on top of sand or loose soil.

How is that working for you? Is it keeping it from sinking? And did you put pavers under the legs?

 

[scout123]

Above ground pools should be set on undisturbed soil because of their weight. Your pool will weight about 58,000 lbs. The foam will not 'hold up' your pool. Foam is basically used for cushioning the floor, making the floor smooth and easier to vacuum, some say it helps insulate from the cold ground; it's not used to support a pool. Having said that, I do recall seeing a post or two of people building a box of wood around the pool to keep the sand from moving out of the pool area. I don't remember them having built up as much as you've done though. I guess if I had to work with what you have, I'd make a box, put a french drain on the wet end to keep water moved out of that area, and add 3/4" crushed stone, compacted, as my base, and then cross my fingers that it all works out. Good luck. It's not an ideal situation, but I hope you find a solution that works for your pool build.

 

[KayDub23]

I thought this may help. Was told by one of the expert builders that cement sand was ok to put under foam board and won't wash out. This is my install thread. SWG & Gas heater that will work on temp & long term pool?

Thanks, the bottom layer is very compacted play sand and the top couple inches are masonry sand, which I understand is concrete sand but with a finer grain.

 

[KayDub23]

Any of the sands I have used have not washed out from under my pool. They cannot wash out. The sand is in a hole such that the top of the sand is even and flush with the soil/landscape surrounding it. If you build up from the surrounding area, then yes it would/will wash out.

You are correct. It may be hard to tell from my picture, but the railroad ties are flush with the lawn and the sand is an inch or two below the tops of the railroad ties. The play sand has been there for 4 years and hasn't washed away, we're not worried about that.

 

[Mermaid Mama]

How is that working for you? Is it keeping it from sinking? And did you put pavers under the legs?

So yes legs will sink if sitting on sand. We have cheap water so we filled it up to see where legs will span too. I was most surprised that the bottom of pool does not make the full foot print. The widest part of the pool does in the middle of the wall. So we put our foam board on the exact footprint of pool. For ours it was 32x16. And our blocks (we used little cinderblock solids that are 8 inch wide by 16 inches long by 4 inch heigh) and made blocks level with pink foam board. We used 1/2" foam board. So most of those blocks were touching or within an inch of that foam board. The best way we found to understand where all the legs were going to be was tie each side to something so that it was not leaning in so much and the legs really didn't move much doing it that way. Our 2nd fill we didn't do this and the legs moved alot and almost came off and a couple got stuck in front of the blocks. Hope that all makes sense. In our case we definitely needed sand bc of rocks. Hope this helps. And it's worth mentioning that exposed sand will wash out but if its covered or has compacted/undisturbed soil around the edges it should be fine. I live near Raleigh and about to have 5 days of alot of rain from this tropical storm so it will definitely be put to the test but so far everything still looks really good.

 

[awhitese]

Above ground pools should be set on undisturbed soil because of their weight. Your pool will weight about 58,000 lbs. The foam will not 'hold up' your pool. Foam is basically used for cushioning the floor, making the floor smooth and easier to vacuum, some say it helps insulate from the cold ground; it's not used to support a pool.

The total weigh of water may be 58,000 pounds, but a 1"x1"x48" column of water only exerts 1.73 pounds per square inch. Under what pressure will the XPS foam board compress? (honest question, I do not know)

 

[scout123]

The total weigh of water may be 58,000 pounds, but a 1"x1"x48" column of water only exerts 1.73 pounds per square inch. Under what pressure will the XPS foam board compress? (honest question, I do not know)

I really don't know either. Let me try @kimkats do you know who could answer this?