Installing a Preformed Garden Pool

Preformed pools are very popular and durable, although they are probably the most expensive. They are made of two kinds of material; plastic and fibreglass. The plastic ones occupy the cheaper end of the range and are vacuum moulded in a tough, yet lightweight material. These are either grey, green or blue and often have a simulated rock finish. For the newcomer to water gardening they are ideal, being light and easy to handle. The only complaint I have about them is their design. With few exceptions they only make scant accommodation for marginal plants.

The same applies to the majority of fibreglass pools. Which is regrettable as they represent an excellent investment for the serious pool owner. Again they are available in a wide variety of shapes, sizes, and colours. However, beware of the smaller kinds referred to in catalogues as rock pools. These are intended to be placed at the summit of a rock garden and act as the supply vessel for a cascade unit. They hold very little water and are generally unsuitable for any aquatic life.

Fountain trays are a similar proposition. Being very shallow they are incapable of supporting any aquatic life. Their intended role is as a pool for the water constantly recirculating through a fountain, or from a gargoyle affixed to a wall.

Installing a preformed pool is not difficult if one knows how to approach the job properly. But it is fraught with difficulties for the uninitiated. Most manufacturers recommend that a hole is dug to the size and shape of the pool. In practice this is virtually impossible. So what must be done is invert the pool in the position in which it is to be installed and mark out a rectangle that will enclose all the most distant points. It does not matter that the pool is inverted and therefore the surface shape is reversed, for the rectangle that is transcribed will be exactly the same size. It is just that it is easier to accurately assess the overall size of the rectangle this way.

The hole should be made as deep as the greatest depth of the pool and the floor levelled up with a layer of sand. The pool is now placed in position and supported on bricks so that it is at the desired level. It should be level from side to side and end to end, yet 3-4cm below the surrounding soil level. Careful levelling ensures that water does not flood out of one end and leave the other dry, while placing the pool slightly below the finished ground level allows for its inevitable rise as the hole is backfilled and rammed firm.

The importance of levelling cannot be over-emphasised, and the use of straight boards on which the spirit level can be rested will ensure accuracy. As the pool is slightly below the level of the surrounding ground to begin with, a short board will be required to level the width and a longer one for the length. These being used continuously during the backfilling process.

If the excavated soil is coarse and stony it should not be used for backfilling as problems with air pockets and subsidence might occur. I always prefer to use sand, filling the hole evenly and gradually removing the supporting bricks. If the sand is rammed tightly around the pool it will provide ample support.

30. July 2011 by Dave Pinkney
Categories: Water Features | Tags: , | Comments Off on Installing a Preformed Garden Pool

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