Making a Garden Pool
Garden pools often become just a muddybecause it is not realized that Nature insists on the ‘correct balance’. A pool can either be formal or informal. It is often quite suitably placed at the bottom of the lawn or near the house as an adjunct to a paved pathway or court. Sometimes it is close to the rock garden and often connected to it by a small stream. Those who only have a small garden may like to make a pool by just sinking a tub into the ground. Never use a barrel that has contained soap, oil or petrol.
The informal pool will be of any shape desired and is generally made to fit into the plan or picture of the garden. If it is intended to stock the pond with fish, shade is necessary, but this should be provided either by tall, marginal plants or by floating aquatics. The dish-shaped pool is easiest to make. The soil should be dug out to the right depth and the soft places filled in with clinker or rubble to get a firm even base. The concrete which should consist of 1 part cement and 3 parts sand should then be ‘spread’ over the depression provided to a depth of at least 75 mm (3 in). Cover the soil with newspaper first before placing the concrete in, as this prevents the soil from absorbing the water from the concrete. A pond can thus be made to any shape but its size should not exceed 1.2 m (4 ft) in diameter and the depth not greater than 450 mm (18 in). Otherwise difficulties always arise when placing the concrete in .
A good pool is one which is rectangular and provides water at varying depths, one end being, say, 300 mm (12 in) deeper than the other. It is also desirable to provide a ledge about 300 mm (12 in) wide and 100 mm (4 in) below the normal water level so that the baby fish find a hiding place during the spawning season. The thickness of the concrete will probably be 100 mm (4 in) in this case. When the position of the pool and the design have been decided on, the soil excavation has to be carried out. Again the bottom of the pool must be rammed and levelled to provide a firm even base. The bottom of the pool should be concreted if possible in one operation and it is advisable to drive timber pegs at intervals across the width and length of the pond, the tops of which should be level with the desired thick-ness of concrete. The concrete should be composed of 1 part cement, 2 parts sand and 3 parts shingle, graded from 20 mm to 5mm.
The pegs should be removed as the work progresses and the top surface finished off with a wooden float. The edges of the bottom slab on which the side walls of the pool would rest should be roughened in order to form a ‘key’ between the sides and the bottom. Concreting should not be done in frosty weather. The sides of the pool should then be built up inside a timber framework which looks rather like a long, narrow, rectangular box, which has to be securely battened and braced to prevent the timber from bulging during the placing of the concrete.
The concrete is filled into the shuttering in even layers, working gradually round the pool and is consolidated with a stout piece of timber. The forms are then left in position for three days and during that period the concrete is kept wet. After this time the timbers are removed and the pond filled with water. Mark one side of the pool with a pencil at water level so that you can see if any noticeable leaking takes place. Before the plants or the fish are introduced the inside of the pool must be seasoned and this means that the water must be left in for a couple of weeks and then the bottom and sides should be scrubbed vigorously with a hard brush. This process should be repeated two or three times.
Another method of seasoning consists of painting the inside of the pool with a 1 in 4 solution of waterglass three times at intervals of three days. Sometimes there are avail-able green and blue bituminous paints which have the same effect, and make the pool look quite attractive when filled with water.
Soon after the pool has been stocked, the clarity of the water will disappear, but if the correct plants and livestock have been introduced to give the necessary balance, the water should clear in a few months and keep clear ever afterwards. Consult a good aquatic nurseryman before starting the pool. You will need floating aquatics, oxygenating plants, ordinary aquatics, ferns or rushes, plus fish, Crustacea and insects. The waste matter which accumulates in a pool is considerable and it is essential that the right plants and ‘animals’ are there to absorb this material. Ten plants are usually necessary to every square metre and it is generally necessary to layer the pond with a good loam spread in the bottom to a depth of 150 mm (6 in). This should be well rammed.