The pool liner offers a greater degree of flexibility than any other pool construction method, but there is a potential for making mistakes at the marking out stage. Indeed, defining the area to be excavated, and ensuring that it meets all practical and aesthetic requirements, is a task that should be carefully undertaken before the liner is purchased. This will ensure that it will adequately line the excavation without necessitating short cuts, which may have undesirable longterm consequences.
Before a definite decision is taken about a pool’s configuration, an approximate shape should be laid out on the ground and adjusted until it satisfies the eye. Even a formal pool with fixed angles and curves should be treated in this manner, so that you are perfectly happy about its proportions in relation to the rest of the garden.
Use pegs and string to outline a formal pool, or a length of rope for an informal pool. A hosepipe is often recommended for this purpose, but many modern plastic types seem to have a mind of their own, making it almost impossible to achieve a smooth curved shape.
When creating an outline for an informal lined pool, take into account that while it is perfectly possible to line almost any shape of excavation, there is a limit to what can be achieved without significant folds and creases appearing in the liner. However, for all practical purposes, if you make any curves or arcs no tighter than could be successfully negotiated with the domestic lawnmower, the liner will usually fit snugly. If the pool is to be set in a lawn with grass to the water’s edge, this will be an obvious requirement.
Having created the shape, take a look at it from all angles. In the majority of cases, the view from the house will take priority, and of course this does not just mean from ground floor level, but from any upper floor, too. Take time to make the final decision, if necessary leaving the line or rope in place for two or three days and then making any minor adjustments as necessary.
Whatever the final shape of the pool, marking out should begin from a fixed point. If you have drawn the shape accurately on a scale plan of the garden, use a fixed point, such as a path or the side of a building, as a baseline. If, on the other hand, the position of the pool and its outline have been established by eye, choose a point at one end to serve as the base point and drive a small stake securely into the ground to serve as a marker.
This is the easiest pool of all to mark out successfully. From your base line or fixed point, determine the centre. Knock a strong stake securely into the ground at this point and attach a string to it, the length of which is equal to the radius of the pool. Tie a pointed stick to the other end of the string and use it to mark the ground as you walk around the centre stake, keeping the string taut. You can make the mark more legible by sprinkling sand or lime on it.
Again, from the baseline or fixed point, establish the centre of the pool and mark it with a garden cane. Take two more canes and mark each end of the oval in a similar way. Then place a stake between each end cane and the centre at a point two-thirds of the distance between them, working from the centre cane. Tie a loop of string around one of the stakes and the end cane furthest from it. Remove the other end cane and pull the first from the ground. Keeping the string taut, use this to scribe an oval shape on the ground around the stakes and centre cane.
A baseline must be established as one side of the pool, using either your existing baseline or a fixed marker. The baseline should be the actual length of the pool and be parallel to, or bear another precise relationship to, other garden features.
Once the baseline has been established, right angles can be created at each end, using the 3-4-5 method. First push a cane into the ground at one end of the baseline. Then mark along the line by 3 units and push another cane into the ground at this point. Next tie a length of string to the first cane with a pointed stick at the other end. Make the string 4 units long and, keeping it taut, scribe an arc on the ground at approximate right angles to the baseline. Use a second length of string (5 units long) and the pointed stick to scribe an arc from the second cane. Where this cuts through the first arc, push a third cane into the ground. A line between this and the first cane will be at right angles to the baseline and can be marked off for correct length accordingly. Repeat this procedure until all four right angles have been laid out.
There are few special considerations when marking out irregularly-shaped pools, except that sweeping arcs and curves are preferable to fussy niches and contortions, which may crumple the liner when it is installed. You can use the principles described for formal shapes, when appropriate, marking out a square or rectangle that embraces the entire pool and using each side as a baseline from which to create the shape.
Place a peg in the centre of the circle. Attach a piece of string the length of the radius of the pool. With a sharp stick attached to the end, inscribe a circle to Mark the outline.
From a fixed point establish the centre of the pool and each end of the oval. Loop a piece of string around the farthest peg. Using the centre cane, tighten the string and mark out the oval.
To create a right angle, mark out a baseline of 3 measures. Fasten a string to each end, one 4, the other 5 measures long. Cross each in an arc to produce the angle of the second and third sides.
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