Installing Your Pool, Stage 3: Laying The Bottom Track

Where you are: your base is level, firm, clear of debris and skimmed with sand. If you are not there yet, go back to stage two.

What you will have finished with: a complete, true circle of bottom track sitting level on your base, ready for the wall.

This is the shortest stage in the series. It is also the one with the least margin for error, and the one where a small mistake is invisible now and expensive later.

Your job today is geometry. Nothing more.

What you are actually building

The bottom track is a ring of channel that the base of your pool wall slots into. It is joined together by bottom plates, which are the flat pieces that sit under each joint and later receive the feet of your uprights.

Together they do three things. They locate the wall. They hold the pool's shape at ground level. And they spread the load of the wall and uprights into your base.

That first one is why this stage matters so much. Wherever you put this track, the wall goes. If the ring you build is slightly oval, or slightly too big, or the joints are unevenly spaced, the wall has to conform to it, and a steel wall does not conform gracefully.

Your assembly instructions are unusually direct about this. They warn that a circle which is not true will greatly complicate the following steps, and could cause irreparable damage to the structure during filling.

That is not boilerplate. It is the manufacturer telling you that a bad circle can wreck the pool.

Before you start: count everything

Open your parts and count the track sections and bottom plates against the parts list that came with the kit.

Roughly what to expect by size:

Count your own box rather than trusting the table. Different production runs vary, and your parts list is the authority. Discovering you are one track short now is a phone call. Discovering it with the wall half up is a lost weekend.

Step 1: Assemble the ring

Work your way around the circle, inserting a track into each side of a bottom plate, then the next plate, and so on until the ring closes.

Lay it out loosely first. Get the whole ring assembled and roughly in position before you start fussing over precision. You want to see the complete circle on the ground so you can judge it as a whole.

Do not stake or fix anything yet. You are going to be nudging this ring around for a while.

Check it closes cleanly. If the last joint does not want to meet, do not force it. Work back around the ring and check that every track is fully seated in its plate. A track that is not pushed fully home takes up slack that shows up at the far end.

Step 2: Get the radius right, measured from the right place

This is the single most important instruction in this stage, and it is the one people get wrong.

Measure the radius from the centre of your pool to the centre of the track cavity, meaning the channel where the wall will actually sit. Not to the outside edge of the track. Not to the edge of the bottom plate.

The difference is an inch or two. An inch or two of error, applied all the way around a circle, is exactly the kind of thing that makes a wall refuse to meet itself at the seam in the next stage.

How to check it: drive a stake at the exact centre of your circle. Cut a string to the correct radius from the centre of the track cavity. Walk it around the full ring, checking at every single joint. Where the string is short, the track is too far in. Where it is loose, too far out. Nudge and re-check.

This is general practice rather than something the instructions specify, but it is the standard way to do it and it works.

Go round more than once. Adjusting one section moves its neighbours. You are converging on a true circle, not fixing it in a single pass. Two or three laps is normal.

Step 3: Check the spacing

The instructions ask specifically that the space between tracks be equal all the way around the perimeter.

This matters because your uprights land at those joints later. Uneven spacing means uprights that are not evenly distributed, which means load carried unevenly and top rails that do not sit right when you get to stage seven.

Measure the gap at each joint and even them out. Small adjustments, then re-check the radius, because the two affect each other.

Step 4: Level the track itself

Your base is level. That does not automatically mean your track is.

Put a level on the track at each joint and work your way round. Look for any section that rocks, sits proud, or has a gap under it.

Fix any high or low spot by adjusting the base underneath, not by shimming. A shim is a point load and it will work its way out over the years. If a track sits low, add and compact a little stone dust. If it sits high, take a little material out.

This is your last easy chance to correct the base. Once the wall is standing in this track, going back is a serious job.

Step 5: Look at it

Before you move on, stand back and look at your circle from a distance, ideally from an upstairs window if you have one.

The eye is remarkably good at spotting an oval. If it looks slightly egg-shaped from above, it probably is, and now is the moment to fix it.

Why the uprights do not go on yet

If you are used to building things, this feels wrong. You have a ring of track with plates that clearly accept upright feet, and the obvious next move is to stand the uprights up and then hang the wall on the frame.

That is not how this pool goes together, and it is worth knowing before you start improvising.

The order in your assembly instructions is: bottom track, then the wall, then the cove and finished sand base, and only then the uprights. The wall goes up first and is held in place with support bars while you work around it.

There is good reasoning behind it. The wall needs to be fed into the track as a continuous unrolling operation, and uprights standing in the way make that considerably harder. The cove and sand finishing also happen against the inside base of the wall, which is much easier with clear access.

So resist the temptation. Leave the uprights in the box until stage five.

Before you move on

• All tracks and bottom plates counted against the parts list
• Full ring assembled and closing cleanly, every track fully seated
• Radius correct, measured from the centre of the track cavity
• Radius checked at every joint, with two or three passes round
• Gaps between tracks equal all the way round
• Track level at every joint, with no rocking or gaps underneath
• Any corrections made in the base, not with shims
• Circle looks true when viewed from a distance
• Uprights still in the box

The short version

• The bottom track decides where the wall goes, so its accuracy is the pool's accuracy.
• Count your tracks and plates against the parts list before you begin.
• Measure the radius to the centre of the track cavity, not the outside edge. This is the most commonly made mistake in this stage.
• Keep the gaps between tracks equal all the way round, because your uprights land there later.
• Level the track itself, and fix problems in the base rather than with shims.
• Walk the circle two or three times. Adjusting one section moves its neighbours.
• Do not fit the uprights yet. On this pool the wall goes up first.
• A circle that is not true can cause real structural damage when the pool is filled.

Next in this series: standing the wall. That is the stage people are most nervous about, and the one where having taken your time here pays off most obviously.