Base Prep On Hard Clay Soil

by Dan
(San Diego, CA )

Hi, I'm building a 15' x 36" round pool on very hard clay. My yard is 2-3 inches out of level, I've read that this is too much.

I plan on renting a sod cutter and removing my nasty-weedy lawn and leveling it out. It won't be smooth due to the nature of my hard soil, so I was thinking of getting the masonry sand, and then a Gorilla liner over that.

But I've read here another user sent the Gorilla pad back and instead used a foam pad of some sort. What is this foam pad called and where can I buy one?

Is it really better than just doing the Gorilla liner over sand?

Thanks, Dan

Hi Dan

What I would not do is level with sand. I normally use the sod cutter and start cutting into the ground once the sod has been removed. If this is not possible I would order something like crushed granite and level and pack the area. I would then put down a couple of inches of sand.

The problem with the Gorilla pad is that it is hard to get smooth and is paper thin once you have a pool full of water over it. There are several different foam pad made to fit your pool, Gladden makes a good one. You could also go to Home Depot and buy 4' x 8' x 1" sheets of foam, these make a nice pool base.

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Jun 11, 2014
Thanks for the quick reply!
by: Anonymous

OK, i think you don't want me to put the sand right on top of the hard dirt because it will eventually settle badly, right?

I do have an RCP nearby and they sell class 2 backfill, a crushed fill like you suggest. I can rent a compactor and make it nice & level, and kinda smooth.

I have read that the foam boards also act as an insulator to the cold ground below, not sure how much difference it actually makes though. Any idea?

I found these at HD, only 1/2 inch though, and I'd need 8, so it's a bit more expensive than a bag or 2 of the masonry sand.

But is this the kind of foam you are referring to?

Would 1/2" be ok or no?


You would be fine with the 1/2" foam over a smooth sand base. Over a dirt base it might be a little thin and I would prefer 1". But, you use what you can get I have never heard mention of the insulation properties in relation to a pool, but it does make sense.

Leveling with sand is bad because it will shift, or wash out, or leave large foot prints in the thicker areas.

The class 2, leveled and compacted, sounds like a good choice.

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