Installing Your Pool, Stage 2: Preparing The Base

Where you are: your circle is marked, the turf inside it is gone, and your sand and stone dust are sitting in the driveway. If you have not done that yet, start with stage one.

What you will have finished with: a flat, firm, level, debris-free base ready for the bottom track to be laid on.

This is the stage worth taking seriously. Everything else in this installation is assembly, where the parts largely tell you where they go. This one is groundwork, where nothing tells you anything and the consequences show up years later.

Here is the honest framing. Water finds level instantly and perfectly. If one side of your base is lower than the other, the water on that side is deeper, the pressure on the wall there is higher, and that section of wall carries a load it was never designed to carry unevenly. It carries it every day for as long as you own the pool. That is how walls bulge, how liners wear in one spot, and how a pool that should have lasted fifteen years comes down in eight.

Take the extra hours here. You are not just making it look right today.

Understanding the two-phase base

Something that confuses people, so it is worth explaining before you start.

Your base gets built in two separate stages, with the wall going up in between.

Now, in stage two, you level the ground and put down a thin layer of sand. That is what the bottom track sits on.

Later, in stage five, after the wall is standing, you add roughly four inches of compacting sand around the inside base of the wall, or install a prefabricated cove, and finish the floor. That is what protects your liner from the edges of the bottom track.

So do not try to build your finished pool floor today. Today you are making a flat, firm, level surface for the track. The soft sand floor comes later, and doing it now just means walking all over it during the wall stage.

Step 1: Get the whole area level

This is the core of the job.

Use a proper level. The instructions suggest an optical or laser level, and for a circle this size that is genuinely the right tool rather than a nicety. They rent cheaply from any equipment yard. A long straight board with a spirit level on it works, but it is slower and more error-prone across twenty feet.

The method most people use: drive a stake at the exact centre of your circle. Attach a straight board or a length of pipe to it so it can pivot like the hand of a clock, cut to the radius of your levelled area, with a level sitting on top of it. Rotate it around the full circle. Wherever the board rides up, you have a high spot. Wherever it swings clear, you have a low spot. This method is general practice rather than something the instructions specify, but it works well and it costs nothing.

Always cut down, never build up. This is the single most important rule in this stage and it is worth saying plainly.

If one side of your circle is three inches high, remove three inches of soil from it. Do not add three inches of fill to the other side.

Undisturbed soil is compacted by decades of sitting there. Fresh fill is not, and it will settle under the weight of thousands of gallons of water no matter how well you think you have packed it. When it settles, your pool goes out of level with water in it, which is a genuinely difficult problem to fix.

Cutting down takes longer and is more work. Do it anyway.

How level is level enough? The instructions do not put a number on it, so here is the general standard the industry works to: within one inch across the entire diameter, and closer to half an inch if you can manage it.

Two or three inches out is not something to accept and see how it goes. That is a reason to keep working.

Step 2: Compact everything

The instructions call for packing the soil with a tamper or a vibrating plate compactor, and note that this matters especially anywhere a lot of soil has been added.

That last part is the key. If you had to add any fill at all, that area needs considerably more compaction than the rest, because it is the area most likely to settle later.

Rent the vibrating plate if you can. A hand tamper works on a small pool and is honest exercise on a large one. A plate compactor does a better job in a fraction of the time, and it costs very little for a half day.

Damp soil compacts better than dry soil. Mist the area lightly with a hose before you compact if the ground is dry and dusty. Do not soak it into mud.

Work the whole area, not just the middle. The perimeter is where the wall and uprights transfer their load into the ground, and it is the part that matters most.

Step 3: Firm up the perimeter band

The instructions recommend adding a thin layer of stone dust, roughly three quarters of an inch, to firm up the edge of the circle, and they specify how wide that dead level band needs to be.

This band is where your bottom track and your uprights sit. It is the part of the base that carries structural load rather than just supporting the liner, and it is the part that needs to be flattest.

Stone dust is the right material here rather than sand, because it compacts to a firm surface and holds its shape under the track. Spread it, level it, and compact it again.

Step 4: Clear every stone, root and sharp thing

The instructions ask you to remove any stone, wood or debris from within the circle, flatten protrusions, and pack the soil tightly.

Walk the whole area on your hands and knees if you have to. Anything sharp is a puncture risk for your liner, and every stone you leave is one you will feel underfoot for the next decade.

Pay particular attention to:

• Roots, especially any that were under the turf you removed
• Small stones that surfaced during leveling
• Anything wooden, which will rot and leave a void
• Old construction debris, which is common in newer subdivisions

If you find a stump or buried rubble, deal with it properly. Filling the hole with loose soil creates a settling problem. Excavate it, backfill in thin layers, and compact each layer hard.

Step 5: The two steps almost nobody knows about

These come straight from the assembly instructions, and they are the reason to read your paperwork rather than a generic guide.

Spread salt over the levelled area. This stops grass and roots growing back up through your base, and it eliminates earthworms. Both are named in the instructions as causes of post-installation cracking in your base.

Spread ant repellant. Same reasoning. Ant tunnelling under a pool base causes settling and cracking that telegraphs straight through the liner.

Neither costs much and neither takes long. If you have ever seen an above ground pool with an unexplained dip in the floor a few seasons in, this is frequently why.

Do this after the base is levelled and compacted, before the sand goes down.

Step 6: The sand layer

Finish with a thin layer of compacting sand, roughly three quarters of an inch, spread across the levelled area. Its job is to protect your liner from the surface underneath.

Thin is correct. This is not the pool floor. It is a protective skim over a base that is already flat and firm. A thick layer of loose sand here just gives you something that shifts under the track.

Damp it and compact it once more. Lightly spray the sand with a hose and pack it. Damp sand holds its shape; dry sand runs.

Check level one final time, with the sand down. This is your last easy opportunity.

Step 7: Stay off it

Once your base is finished, treat it as done.

Wear light, flat-soled shoes for the rest of the installation. The instructions specifically warn that the slightest heel mark can be visible once the pool is filled, and they are right. A boot print pressed into a finished base is still there under the liner years later.

If you have to walk across it, walk gently and rake out your tracks behind you.

What good looks like

Before you move on, stand at the edge and look across it. You want:

• A flat, even surface with no visible high or low spots
• Firm underfoot, with no give when you press down
• No stones, roots or sharp debris anywhere
• A level reading within an inch across the full diameter
• No footprints or tool marks
• A clean, defined perimeter band ready for the track

If any of those is not true, this is the cheapest possible moment to fix it. Every stage after this one makes going back harder.

A note on time and expectations

Our customers consistently tell us that leveling is the hardest and longest part of the installation, and that they wish they had allowed more time for it.

If your yard is genuinely close to flat, this is a few hours. If it has real slope, it can be a full weekend and it may be worth hiring someone with a machine for a day. That is not a failure. Cutting a level pad into a real grade is earthmoving, and earthmoving is what equipment is for.

Whatever it takes, it is time well spent. This stage is the closest thing to a lifespan setting on your pool.

Before you move on

• Whole area level within an inch across the diameter
• All leveling done by cutting down, not filling
• Any added fill compacted hard
• Whole area compacted with a tamper or plate
• Perimeter band firmed with stone dust and dead level
• Every stone, root and sharp object removed
• Salt spread
• Ant repellant spread
• Thin sand layer down, dampened and compacted
• Final level check passed
• No footprints, flat-soled shoes from here on

The short version

• Water finds level perfectly. Your base needs to be within an inch across the diameter, ideally half.
• Always cut down. Never build up. Fresh fill settles and takes your pool out of level with water in it.
• Rent an optical or laser level and a plate compactor. Both are cheap for a day.
• The perimeter band is the part that carries load, so firm it with stone dust and get it dead level.
• Clear every stone and root, and deal properly with any stump or buried rubble.
• Spread salt and ant repellant. Roots, earthworms and ants all cause base cracking later.
• Finish with a thin sand layer, damp it, compact it, and check level one last time.
• Flat-soled shoes from now on. Heel marks show through the liner.

Next in this series: laying the bottom track and setting the uprights. That stage is where your circle has to become geometrically true, and getting it right depends entirely on the base you have just finished.