What to put under an above ground pool: ground, base and levelling
What you put under an above ground pool matters almost as much as the pool itself. Every 10 cm of water weighs 100 kg per square metre, so a pool 1.20 m deep puts about 1,200 kg on every metre of ground. With that in mind, the rule is simple: the ground must be firm, level and free of anything sharp.
What does the ground need?
Three things, and none of them is optional:
- Firm: it must not sink under the weight. A soft patch ends up forming a hollow under the water and the pool loses its shape.
- Level: no more than 2–3 cm difference between two opposite points. With a bigger slope the water looks crooked and part of the wall takes more pressure than the rest.
- Clean: no stones, roots, branches, screws or anything pointed. The floor is PVC: any bump can be felt underfoot and wears it over time.
Also plan the space: the size of the pool plus about 50 cm all around to move, and to place the ladder and the filter pump.
Which surfaces can it go on?
| Surface | Does it work? | What to put on top |
|---|---|---|
| Natural lawn | Yes, if it is level | Geotextile mat |
| Artificial grass | Yes, one of the best | Nothing else, if it is smooth and level |
| Tiles or concrete | Ideal | Geotextile or foam tiles |
| Wooden decking | Yes; if raised, with a load calculation | Geotextile, checking screws and splinters |
| Compacted fine gravel | Yes | Thin layer of sand and geotextile |
| Soil | Yes, after levelling and compacting | Geotextile mat |
| Loose sand, a slope or an unchecked rooftop | No | — |
What is best to put underneath?
For most gardens, a geotextile mat of 200 to 300 g/m², the same kind used as a weed barrier. It is cheap, cut to size and keeps the pool floor away from small stones, roots and insects. Leave it about 20–30 cm larger than the pool on each side.
If you want extra comfort, interlocking foam (EVA) tiles are the best option: the floor feels soft underfoot, they protect better against any bump and insulate from the cold ground, so the water warms up a little sooner. On tiles or concrete they are almost essential if you will spend many hours in the pool.
What to avoid: thin plastic sheets, which wrinkle into hard folds, and old carpets or rugs, which hold moisture and smell within a few weeks.
Can you put sand underneath?
Only as a thin levelling layer: 2–3 cm, damp and well compacted, and always with the geotextile on top. A thick layer of loose sand seems comfortable, but under the weight of the water it shifts, footprints show in the floor and bumps and dips appear within days.
How do I level the ground?
- Mark out the area with stakes and string, including the margin all around.
- Check the slope with a straight board and a spirit level, crosswise and diagonally.
- Remove soil from the high side instead of filling the low side: filled soil, even when trodden down, tends to settle under the weight of the water.
- Compact with a tamper or a garden roller, and measure again.
- Clean away stones and roots, lay the geotextile or the tiles and set the pool up on top.
Once the pool is set up, fill just a few centimetres and look at the water: if it reaches one side more than the other, you still have time to drain and correct it. We explain it step by step in How to Set Up a Portable Pool in 20 Minutes.
What happens to the lawn underneath?
Without light, the grass turns yellow within one or two weeks. If the pool stays up all season, you will usually need to reseed that area when you remove it. If you want to keep the lawn, the alternative is to set it up on a tiled or gravel area, or to lay artificial grass just in that space.
And on a terrace or a rooftop?
There the problem is not the surface, it is the weight. Even the smallest pool, an Azora XS 2 m across and 50 cm deep, weighs about 1.5 tonnes when full, around 500 kg per square metre. Before setting up any pool at height, ask an engineer whether the structure can take it. We give the figures in portable pools for terraces: weight and safety.
In summary
Firm, level and clean ground; on top, a geotextile mat or foam tiles; and no loose sand or slopes. On that base, a pool with rigid Drop Stitch walls stays straight and stable all season. If you are still choosing a size, you will find every option in our above ground pools.