It is surprising that books and articles on pond construction say so little about raised ponds, bearing in mind the number ol advantages they have over ground-level and sunken ponds:
A number of advantages, but there are also two important drawbacks. The small raised minipond on a patio looks attractive, but a large raised pond can look out of place in many gardens. Secondly, the superb insulating properties of the soil around a ground-level pond are lost — this means that freezing in winter and overheating in summer are more likely.
The smallest type is the half-barrel, deep trough or sell-contained pool/fountain unit on the patio — see the minipond section on page 65 The simplest form of walling around the larger raised pond is an earth bank around a Rigid liner — easy perhaps but not appealing in most garden situations. For more suitable suggestions see the diagrams on the right
Rigid liner with sand base
Flexible liner folded at corner — polystyrene insulation
RIGID LINER Use a fibregiass liner — choose a simple shape. Walls can be made of brick, btocks of concrete or reconstituted stone, or railway sleepers — the best choice depends on availability, personal taste and shape. Provide a firm foundation and rem em tier that an inner wall is necessary to support the marginal shelf.
FLEXIBLE LINER Use butyl sheeting — choose a simple shape for the pond Compared with the Rigid liner pond the walls will have to take a much greater strain from the weigh t of water and the thin liner has little insulating effect For a pond of 40 sq.ft the wall should be two blocks thick. Use polystyrene slabs for insulation. Make sure mortar is set before folding in liner and filling with water
NO LINER it Is possible to dispense with a liner if the brick or block wall is well made with firm foundations and surrounds a strong concrete base The inside can be rendered with cement to improve the appearance — this is optional but painting the inside with two coats of pond paint is absolutely essential. Follow the instructions on the tin exactly. A marginal shelf can be built in the same way.
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