"> Does an above ground swimming pool need a hard base material? – Above Ground Pools Know it All

Does an above ground swimming pool need a hard base material?


It’s common for people to install their own above-ground swimming pool. Depending on the type and size of the pool, the project can be a pretty big one.

With most DIYers knowing nothing about installing above-ground pools, they have to research everything. Researching what to put down in the ground to keep the pool from settling is important.

With almost all above-ground swimming pools, no added base is needed for the earth. If installed properly, an above-ground pool will not settle. Only small areas on the pool’s bottom can sink down, but not a large area or the entire pool.

Does an above ground swimming pool need a hard base material?

WHEN SELF-INSTALLING AN ABOVE GROUND POOL, SOMETIMES TOO MUCH CONSTRUCTION KNOWLEDGE IS A BAD THING

Some guys that build things can be a pain to deal with when it comes to installing a pool for them. And engineers are the worst. They try to use the logic from their jobs and apply them to above ground pool installation. Yeah, that doesn’t always mix well.

When it comes to whether an added base is needed or not for an above-ground pool, some ground-up construction rules don’t apply. A hard base is not needed for an above-ground swimming pool.

ALLOW ME TO INTRODUCE MYSELF

Before anyone reading this thinks that this is bad information, know who is telling you first.

I have been an above-ground pool installer for 35 years and installed more than six thousand of every type, maker, and model of pool that exists. Most of my installs were in Central Florida but I did do a few one-season up in Georgia (oh that Georgia clay).

Having installed pools partially in the ground, completely in the ground, on top of the ground, and even on completely built-up hills. I have also leveled the earth and built up the low end of pool locations two-three feet high, and no pool ever settled. Period.

Here in Central Florida, everything is built on sand. I once saw a large retail center built up on a hill. Forty feet thick of earth was added to that hill to level it out enough to build the retail buildings and parking lot. That was 30 years ago, and everything is still there with no movement.

So, if a shopping center built up 40 feet in the air with just sand-based earth doesn’t move/settle in more than thirty years, don’t think an above-ground swimming pool will settle much.

THE EARTH IS DEFINITELY DYNAMIC, BUT NOT ENOUGH

Coming from a guy who has built on the earth for decades, I can tell you that the earth is alive and well. What the earth’s surface is made of and what is growing and living in it creates so many variables when installing a pool on it.

Different aggregates hold or repel moisture. Plant life and roots push the earth around, create voids, and are a part of an ecosystem with its own dynamics and cycles.

Bugs and critters of all kinds burrow, nest, and look for food in the earth. Then there’s the dynamic of bacteria in the earth and how it forms and changes the aggregate around it.

All of the above factors make the earth move around a little, but these vibrations aren’t enough to affect the properly installed above-ground swimming pool structure above it.

AN ABOVE-GROUND POOL IS HEAVY, BUT THE WEIGHT IS VERY EVENLY DISTRIBUTED

Water is really heavy. Each gallon of water weighs 8.3 pounds/3.8KG, so a 24’ round pool (most common size) with fourteen thousand gallons will weigh 116,000 pounds.

That’s a lot of weight pressing down on the earth, but it is so evenly distributed that it’s not that bad.

Some will mistakenly think that the wall of the pool has a heavy downforce. That’s why they think thick blocks are needed to support it under each upright. In truth, the pool’s wall has very little downforce and the patio blocks are not needed for support.

The patio blocks used under each upright are optional. When I started installing above grounds in the eighties, we didn’t use patio stones. Earlier this year, I disassembled a 15’ round in downtown Orlando that was only a year old. It was installed by a guy who has been an installer for 15 years. This pool didn’t have any supports under the uprights and it was perfectly level.

I always use patio stones under each of the pool’s uprights, but not for any structural reason. I use them so I can get the bottom track perfectly level and use them as a reference point when rolling the wall in place (the bottom track can move around some when inserting the wall).

ARE SOME AREAS OF THE PLANET MORE DYNAMIC THAN OTHERS?

I ask this question because some have argued with me that the earth moves where they live and not in Florida. Of course, there are areas of the planet that have some plate dynamics and therefore have earthquakes and tremors.

Even an earthquake may not affect an above-ground pool if no part of the footprint of the pool moved away from itself. And that’s the most extreme dynamics that exist.

Some will argue that their area settles more than others. Again this can be true but not likely as any area that gets that much settling probably won’t have a house or any type of permanent structure anywhere close.

THINGS THAT CAN CAUSE THE EARTH TO SETTLE UNDER AN ABOVE GROUND POOL

There are really only two things that can make the earth settle downward under an above-ground pool.

1. Air in the earth

Typically, the earth will have three things in it – aggregate, water, and sand. The type of size aggregates in your yard can vary from big rocks with clay to pure sand (essentially tiny rocks) like in most of Central Florida.

The aggregate cannot change in size much. Most things that make up the earth are whatever size and shape they’re in and although may be breaking down into something smaller, it will take years for that to happen to any big degree.

Now, the aggregate (earth) can have some air and moisture in with it. Air can be in between the aggregate causing the earth to take up more volume or be “fluffy” so to speak.

This is what happens when you dig a hole and there seems to be more dirt when you fill the hole back in. The action of removing the earth (from the hole) adds air to the aggregate, thus making it more voluminous (if that’s the correct word).

So, if you install an above-ground pool on volumized earth, then the weight of the pool water will eventually cause the earth to press down and release some of the trapped air. This will take some volume out of the earth and the level will settle down some.

NOTE: Spraying the earth with water a couple of times and/or tamping the earth that makes up the pool’s bottom will release the air in the earth. This is what is meant by “packing the earth down”.

2. Decomposable materials in the earth

Anything in the ground that can rapidly decompose or break down can cause the earth to settle.

There are tree roots below the earth’s surface everywhere. Most of these roots are too small to make a difference in the volume around them when they die and decompose. Plus other roots are constantly growing to make up for the lost space.

Bigger tree roots or tree bases or trunks can cause some local earth settling though. Different tree roots decompose at different rates. Most will rot away without displacing the earth surrounding it much at all. Other roots (especially from trees that were cut down) may decompose very rapidly and thus cause voids in the earth. And these voids will be replaced by the earth lying above them. This will cause some earth surface settling.

Some trash that has been buried can decompose quickly and cause the earth to settle too. Anything foreign to the earth can cause eventual voids in it which will be replaced by the dirt sitting above it. This will cause settling as well.

Professional installation tip: When preparing the earth for an above-ground pool, it’s best to remove any large tree roots or foreign matter (like from an old trash burn site) from the earth. This may prevent an uneven pool bottom later due to decomposition.

EARTH SETTLING IS NOT THE CONCERN – EROSION IS

Taking steps to re-enforce the earth from settling under and around your above-ground swimming pool is a waste of time and money. Making sure to prevent any erosion from happening isn’t.

Erosion happens when the earth is displaced (carried away) by the flow of water.

If water can flow in any way and any direction at any time next to your above-ground pool, then that is cause for concern. In most cases, (rain) water can only flow when there’s an elevation difference or slope in the yard.

The water will travel from the high part of the yard to the low part due to gravity. Duh! This moving water will take with it any aggregate (earth) light enough to move and displace it at a lower part of the yard. This is what erosion is.

If you have moving water in your yard during any extreme weather situation (even if it’s only like once a year) AND this moving water is close to your pool, then you should address this issue.

Preventing erosion can be as easy as putting down a layer of rock around the pool (to prevent the water from taking the earth away) or as hard as having to pour concrete and build retaining walls. Whatever it is that you have to do to prevent erosion around your pool, it’s worth doing.

DOES YOUR REGION HAVE “FROST HEAVING”? THEN ALL BETS ARE OFF

Fortunately, most areas that people live in aren’t super cold climates. If you live in the extreme north though, you may have a condition called “frost heaving”. And if you do, then you may have to take an extra step or two when installing an above-ground pool.

Frost heaving happens when the earth freezes, then thaws, then freezes again. This makes the earth do crazy things. One thing it can do is push your above-ground pool upward on one side, thus making it off level quite a bit.

If your above-ground pool is completely above the ground, then it shouldn’t be affected by the earth underneath it expanding and then thawing. This will be an issue if your above ground pool is in the ground at all in these areas.

Assuming you live in a area with frost heaving, it may be a good idea to lay down a hard base under an above-ground pool. This base would have to be below the frost line of the earth and be made of a material that won’t hold much moisture.

A HARD BASE IS NOT NEEDED TO INSTALL AN ABOVE GROUND POOL, BUT A SOFT ONE IS

What I mean here is that you want a layer of material that can be soft enough to make it smooth for the bottom of the pool.

When it comes to pool bottoms, smooth and flat are best. You don’t want anything too hard, bumpy, or full of rocks, sticks, or things that you may feel when swimming.

Most above-ground pool installation manuals will tell you to use sand as a base. Sand is good as long as it’s not too thick as sand can be very soft. The good thing about sand is that it is clean and free of any objects that you might feel on the pool bottom.

For me, a clean darker earth (soil-like) with some clay in it makes the best pool bottoms. It is denser than sand, so it will hold less air and water, which will allow it to pack better and stay smoother during the final stages of the installation.

And the clay aggregate portion is nice in that it hardens the earth some after it dries, which helps keep the bottom smooth.

danknowitall

Dan writes with the knowledge of having 35 years (and counting) in the above ground pool industry.

31 thoughts on “Does an above ground swimming pool need a hard base material?

  1. My husband brought home what I’m guessing is an 1990s style pool. No instructions just that everything is in excellent condition (Obviously depending on who you ask) we just needed a liner. It’s 15ft round above ground pool and only enough “tracks” more like tubing, both metal and rubber. Apparently according to said person there is supposed to be no bottom track….that the vinyl wall sits on earths ground. not only that but there are no uprights either?!! The tubing she claims goes on top of the pool wall. Help! I think there should be both top and bottom rails as well as uprights and a top rail that also wasn’t supplied. My husband wants to put up the pool per the old owners instructions and I’m struggling here. Why believe your wife when you could believe a stranger?

    1. I’m sorry. There’s just too much of this post that I don’t understand. No bottom track AND no uprights? So, the pool is not up? It would take a few pictures for me to help here.

  2. I am putting up an oval 12×24 above ground pool. After grading the area I realized that there are areas that are spongey. My soil is mostly all clay. There are areas that just will not compact. The ground just keeps giving in those areas. It’s like you can bounce on it and it settles lower. I am at a loss as to what to do to those areas. Will the ground hold the weight of the pool?

    1. Unless you have some super weird situation with your ground, I think you’ll be ok. In my experience, “spongy” always means moisture. I don’t know of any earth that is spongy without water in it. You may want to wait until the earth dries some and then see.

  3. Hey Dan, I found this site searching pool installations. I really like all the information here. This is gonna be a bit long but I have a few questions. Unless you take phone calls. We had an above ground for many years and got rid of it, and now we are doing it again. I went out of state (the pool places here suck) to buy the pool we wanted, 30 Ft Carvin Downtown and I am installing this one my self. I am confident I can do it and pretty OCD about things being done correctly. I see a lot of different opinions on getting earth ready and the base done and this is the part I want to get right. An excavator friend of mine is doing the digging and leveling with a Transit, we have about a 2 ft drop. The plan is to cut from the low end and build a retaining wall on the high side. The pool company that I bought the pool from told me they just use enough sand to smooth out any imperfections in the dirt and use the foam pad and cove. I plan to rent a tamping machine. They said to get 3.5 tons of sand and use the patio blocks under the uprights. The pool manufactures instructions call for a rock dust base (about 6 tons). According to this post, if done right I don’t need a base and just the earth. Im in Kansas City and our ground is mostly clay. Are they correct in just using enough sand to smooth the ground? Watching your install video, as you leveled the bottom track, did you backfill under the track with dirt if there were voids from leveling? If so, what keeps those small areas of back fill from settling out? My guess is it would be hard to pack good being under the track. Do I have to be concerned with the patio blocks settling/moving? Thank you, and I look forward to your input.

    1. 1. Don’t need a stone dust base.
      2. Only need enough sand to make the bottom level and smooth. Any more than that and the bottom will be soft and harder to get smooth.
      3. Don’t need to compact the earth (Plus, sand doesn’t pack anyway.)
      4. I make sure the earth near the bottom track is firm only by either pressing down with my foot or tamping the cove with my concrete come along (concrete placer) tool. I also make sure and backfill dirt along the outside of the bottom track to make sure it’s got dirt under the track.
      5. Patio blocks shouldn’t move at all. There is very little down force on them.

        1. I don’t know. It depends on your existing earth and how level you were able to get it. If you are using some sand to help level your bottom, then you may need 3.5 tons. If the ground is nice and flat and you are using foam coving, then 1-2 tons for a 30′ round is all you’ll want.

          1. Ok, also have the what they called the gorilla pad. Which is just 1/8 giant rolls of foam for the bottom.

          2. A gorilla pad is NOT foam padding. It’s a synthetic material that can transfer moisture. I recommend that over 1/8″ foam.

          3. Hey Dan,

            There’s a lot of great information on here! We bought a 12×24 oval pool and have had a lot of issues with the spot. A lot of different installers are telling us different things. When we excavated the spot, we hit rock. Our entire backyard is rock. So we brought some dirt back onto the rock to level everything off and then brought in 4” of sand and packed it down. We’re being told we should put screenings down first under the sand to pack like concrete or we should’ve put 1” clean under the sand, etc etc. Getting a lot of bids for pool installations that are going to cost more than the pool itself. What is your advice on what would be best? Thank you for any help you can give!

          4. First off a disclaimer – I am extremely familiar with the earth in Central Florida (which is mainly sand based) and some of Georgia (which is clay based), but not with an area like yours (which sounds like it’s rock based).

            That said, I can tell you this – Most builders outside of Florida think an above ground pool needs to be on a solid base. And it doesn’t. If your bids are coming from contractors with limited above ground pool installation experience, then it’s common for them to think you need to do extra things in the earth when you don’t.

            My thinking is to get the area as level as you can, then dirt like you said, then if the dirt is not clean, a layer of clean sand on top to make a nice pool bottom with.

            Since you have an oval pool, plan on the dirt/sand base being at least five inches deep. You are going to need 3-4 inches of depth to set and bury the buttresses, water(bottom) plates, and straps.

            Also, your area may have some unique earth dynamics that I’m not aware of (I doubt it though), so talking to a very experienced above ground pool installer from your area is the best. And even with that, if he has only been installing the way he was taught years ago, he still may be taking unnecessary extra steps with the earth.

  4. Wouldn’t that mean the foam cove act the same as the foam bottom? I guess I don’t understand why one is better than other.

    1. A foam coving and a foam bottom are two different things. https://abovegroundpoolsknowitall.com/what-is-above-ground-pool-cove/

    1. 1/8″ foam is too thin. It’ll just get in the way of installing the liner and won’t offer any added protection. And if taped together well, it might even trap miosture. If you want a foam bottom, then go thicker foam boards.

  5. What I have is just what came with the pool. If there is a better option i want to get before install. If the Gorilla Pad, Rhino Pad etc is better than that what i will do.

  6. Hey Dan,

    I am installing an 18×33 pool off the back of my house, connected to the home by a deck. The deck is 20×20 and will contact the pool on the far side. From one corner to the other of the pool longwise, heading away from the house longwise is 16″ of elevation change. I cannot lower the leading edge of the pool 16″ because it will not work with the deck, so my plan is to build up the far side with crushed stone process. What are your thoughts? I can bring the deck side of the pool base down about 6″ and bring the far side of the pool base up 10″. I already have plenty of crushed process and mason sand, and the pad is almost prepped, and deck footings in place, so figuring out this last part is my sticking point. Thanks for your help!

    1. Hi. I think that you are asking if it’s ok to build up your yard some to make the pool level. Yes you can. I do it all the time with no long term issues.
      I would like to add though that you’ll want to create a ledge that goes out and away from the pool where you build it up. You don’t want to have a fast drop off from where the pool is. Build it out at least a couple of feet And then make sure there will be no future erosion by grassing it or bordering it with rocks or something that will prevent water from carrying your ledge away.

  7. I think my other question is if you were in my situation would you use stone dust/stone process to build that area up? I was told it will get real hard if tamped down and weted with water. I am planning on building up the whole pool base out of crushed process, then using pool sand inside the walls for the base, I have a fabric barrier I bought from the pool company for between the sand and the liner, and foam cove. I think you answered my question about how to bring the base away from the pool wall, for drainage. I will also be using a granite 3/4 stone for around the pool also. So I will heap that on top of the process edge that is exposed. Thanks!

    1. If you have plenty of that material AND it won’t prevent things from growing in that area (if you are planning on some grass or plant life there), then yes, sure. Any kind of earth should work well too. It’s not so much about what you use to build an area up as it is how you manage the surface area to prevent any possible erosion.

  8. I appreciate all your advice here Dan. Today we dug down the high side to try and lessen the difference between high side and low side. The person helping me prep the pad thinks we should use 3/4″ stone process crusher stone and build a level 8″ thick pad for the pool, then, Put the stone dust on top of that. This will also help to bring the pool to the hight of the deck we are building. He said it will create a strong level and even area that will prevent erosion. What are your thoughts on this? Thankss again for your advice. Ryan

    1. I say to do whatever makes you feel good about the pool install. I have to ask though – Do you plan on a lot of water moving next to your pool in the future, like a little creek or river?

      I ask because this would be the only reason to worry about erosion. Erosion is water displacing earth. Can that happen under a pool? It can but is super rare. And even if there was water moving the earth under the pool, do you think any material would stay in place as water moved through it? Even a concrete pad would eventually be affected by erosion under it as it would create a void underneath.

      In reality, the only erosion that an above ground pool installer worries about occurs at the earth’s surface (immediately around the pool) usually due to heavy rain and is not constant. This is why you only have to worry about earth being dragged away at the surface and temporarily. This is why only a layer of rocks at the surface is needed. And that’s if there’s a condition for erosion, which there usually isn’t in most places.

      1. The reason for the 3/4″ process is to build up the surface to the deck level, which comes off of my house. I guess, my question ultimately is if you needed to build up the hight of an above ground pool, would 3/4 process be what you would use? Thanks,

  9. Dan,

    So if I read this all right, as long as I am preventative about erosion, placing my pool legs on pavers set in sand and building the walls on sand won’t be an issue. Have to make sure to prevent erosion Best I can. Understanding that being in Wisconsin, there may be some issue with frost heaving. Which would be an issue regardless of if I set my pool legs on pavers set on earth or sand.

    1. I have the same question… is it ok then to install everything on compacted level sand as long as erosion is addressed? Thanks so much

      1. Yes absolutely. I essentially install most of my pools on a sand base(because I’m in Central Florida). The issue with using too much brought in sand is that it doesn’t pack, so it can be too soft and you may have footprints. That’s it though.

  10. Hi Dan

    Great information you’re sharing with everyone! I tried to read through all of the comments to see if you’ve covered what I’m going to ask but didn’t see anything on it… So I’m literally in the process of installing an 18×54 round, semi-inground- my buddy used his mini excavator and transit to prep the area. The ground packed nicely and is very level. (Orange claysand in South Carolina) has been great to work with. After we put the bottom track and walls up, installed the foam cove and foam wall, and felt mat, we were ready to install the unibead liner. The issue is, I missed the part where the instructions said to add 3” of base sand to bring the floor height up so the liner would not have any air gaps near the cove area and to prevent the pool walls from collapsing due to too much pressure (liner stretching) because apparently unibead liners are made to the wall height with the 3” sand base factored in. Completely missing/skipping this step, I made sure all wrinkles were out and started adding water this afternoon. Currently there is about 4-5” of water and everything looks good so far- liner does seem to have about 2-3” gap between wall all the way around, so I thought about adding a vacuum now, just to bring the liner in snug to the wall, before too much water was added but instead while googling the vacuum method, I saw a post about how I must add the 3” base. Am I in trouble and need to drain and pull liner out to add the base? The pool is positioned in the path of about 14hrs of southern hot sunshine and I was hoping it will help the liner stretch and adjust by the time I come home tomorrow after work and then I can just proceed with filling and maybe add the vacuum as well. Sorry for the long post but I don’t know if I need to proceed with filling with water or add the sand. I appreciate you’re reply.

    1. It sounds like you are more than good to go. The coving does not have to be that tall or big. I install pools with foam coving almost every day during the summer and usually only cover the bottom rails with an inch or so of packed earth and then apply the peel and stick foam coving on top of that.

      The liner will stretch with no issues. The liners are made to be a little smaller than the pool so then adding water stretches the liner out to the wall and in a perfect, wrinkle-free form. No vacuum is necessary. I haven’t used a vacuum in 30+ years)except for the few times I was setting a liner with a doubel deep center at one end of an oval.

      1. Hi Dan

        Thank you for the quick response! I am glad to know that I do not need to go back and add thickness to the base, this is a huge relief.

        Also after knowing the water pressure will set the liner in place, i don’t think that I will use the vacuum after all! So far, the wrinkles on the walls are extremely minimal and look as if they will flatten with no issues once water has reached them.

        Now, when it is time to add the return port and skimmer hardware, I would assume the liner will have then pressed close enough to the wall that I can do a clean install on both and not have any issues with the liner stretching at the screw points. Should i wait until the water is just below them or sooner?

        Thanks again!

        1. As a pool installer, I have no choice but to cut the openinings with only a few inches of water in the pool. As a pool owner though, wait until the pool is at least half full and the liner is completely pressed against the wall. It’s easy then.

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