Bottom of pool is very bumpy!

[tnt69]

I installed a 21 X 43 foot AG pool 2 1/2 years ago. It has a sand base under the liner and the sand has all sorts of irregularities and bumps and along with the sand cove also breaking down it is a nightmare to clean and looks bad on a nice sunny day to boot. I want to drain and remove the liner, which also has many wrinkles, and put in some sort of firmer base. What is the best recommendation for an AG pool base? Poolcrete or foam for under the liner? Or something else?

[CarlD]

At this point, the chance of your being able to remove and re-install the same liner are rapidly shrinking. It MAY still be possible but be prepared to replace the liner.

It sounds like your base isn't stable and there's water under there causing the sand to shift and wash away. I'm guessing on this.
You probably want to dig out the material under the pool, and fill it with crushed stone or QP (Quarry Product) and then fresh WET sand on that to get a smooth base. You may even be advised to put a French Drain under everything to move away water under the pool.

Just thinkin'

[tnt69]

Actually, we have a large french drain under the pool and a small part of it (about a foot and 1/2) has settled a couple inches causing another spot where the pool is low. I don't think there is a problem with the sand washing out but the fact that the sand probably wasn't wet enough and didn't get tamped down as well as it should. The irregularities are simply foot prints and spots where the sand settled along the pool bands that run across from wall to wall and around the cove. Are Poolcrete bottoms a better way to go or simply too expensive? Also, what about pads over the sand? And Foam coves? Do they help or cause problems down the road? Also, this was actually our 4th year for the pool so if the liner needs to be replaced, we would be prepared to do that.

[CarlD]

I cannot answer your other questions, but tamping is part of the process. The QP under my pool was tamped very thoroughly but while the original install was fine, the liner failed after 10 days. The warranty guys who re-installed the liner, didn't know how to handle sand and kept whining that I should put in a vermiculite base. Consequently, they didn't wet the sand, didn't use flats of plywood as "snow shoes" and I had wrinkles and ugly footprints for 12 seasons. I am now in rebuild mode so the liner and the walls are down.

We do have users that have tried the foam base. I'm going to use foam on the walls, but not the base. Perhaps someone can relate their experience with that.

[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?