Bottom of pool is very bumpy!

[tnt69]

Yes, I am also considering foam on the walls. We like to open in April and close around the 1st of November. We are in Southern Illinois and have a gas pool heater but I would like to know if anyone has the foam on the walls and floor and if they really think it helps keep xtra heat in and if the pad on the floor helps with bumps and such.

[SunnyOptimism]

I think there's two issues that could/should be addressed - water flow under the pool and proper compaction of the base.

One thing you could consider for water flow and compaction is to construct a concrete footer around the perimeter of the pool. You'd need to probably dig down anywhere from 12"-24" and fill the trench with concrete and cinder blocks to create a wall around the pool base. The outside of the footer should have crushed fill stone #3 size (1/2" to 2") and, possible some drain pipes. The interior of the pool base could start with a layer of poured concrete onto which you place large stones (#2 or #1). If you don't want a solid base of concrete you could just do stones but you should use a plate compactor to create a solid base of stones that are "locked" together. Landscape drain pipes should also be used at this level with passage through the cinder block footer to relieve any water that might get under your pool. The final layers should be successively smaller stones or pea gravel with the very last layer being decomposed granite (DG) fill material. Sand certainly makes a finer/smoother base but I would be very wary to use it as sand is easily moved around and, as you have witnessed, you can lose sand and get an uneven base. DG is a bit more coarse but is also more dense and does not move as easily. Since you live in a cold climate where freezing and thawing is an issue, proper drainage and compaction is key to making sure frost heaves from freezing water does not ruin your pool base.

The only other option is to try to build a water-proof base using vermiculite board but that would require a much more detailed layout.

Just my opinion I did paver-stone hardscape in my backyard and artificial grass with a retaining wall enclosure and it took quite a lot of work to make sure the ground was stable underneath it all. Even with all the effort we put into it, there is still one small section of the turf where I can see a little trough that developed in the DG base layer because the gas line trench was not fully compacted after it was dug out and refilled.

[tnt69]

I'm sure my problem is simply the sand underneath NOT being wet enough and compacted enough. I watched the installer as they spread the sand. I did not think they watered it near enough (it was dry sand) and they didn't spend much time tamping it down. The sand cove has settled a lot also.
I would like to know if anyone has had good luck with foam between the sand and liner or a Gorilla Pad or similar and foam coves also? And also, has anyone used PoolCrete under an AG pool and what kind of expense is that?