Liner Dimensions

The majority of pre-packed liners will state the pond dimensions which they are suitable for, but if you buy liner from a roll then you need to work out how much you need. Decide on the dimensions of your pond, marking the site out with string and pegs to check the finished effect. The liner should measure the maximum width of the pool plus twice its depth, by the maximum length plus twice its depth. Add a further 15-30 cm (6-12 in) to the liner width and length to allow for an overlap around the edge.

Liner width = Maximum width + (2 x depth) + 15-30 cm (6-12 in)
Liner length = Maximum length + (2 x depth) + 15-30 cm (6-12 in)

Preparing the Ground

Level the ground as much as you can before you start to work; check this with a plank and spirit level. Liners can be pierced by couch grass roots, so make sure that the area is completely clear - use a suitable weedkiller, such as one containing glyphosate.

Digging the Hole

Mark the outline of the pool using string and pegs, rope or a length of hosepipe; a round pool may be created by swinging a line from a central stake. Dig the hole to about 23 cm (9 in), making sure that the sides slope at an angle of about 20°. This will prevent the sides from caving in and will also make it easier to install the liner. This first level will form the marginal shelf. Mark a line so that the shelves are approximately 23-30 cm (9-12 in) deep, and then continue digging (still at an angle of about 20°) to the required depth - about 45-65 cm (18-26 in) is usually quite adequate. As you dig, remove any sharp objects such as stones and plant roots that could pierce the liner. Tamp down the soil firmly.

Remove a 30 cm (12 in) strip of soil around the perimeter of the hole to hold the coping stones. Dig to a depth of around 5 cm (2 in). When you have finished digging, make sure that the rim of the pool is absolutely level using a plank and spirit level.

Lining the Hole

Protect the liner by laying a protective layer over the soil. You can do this by spreading a 5 cm (2 in) layer of damp sand along all the surfaces, working up from the bottom. Apply a slightly thicker layer to the base.

Alternatively, lay an undersheet of fibreglass loft insulation or polyester matting to cushion the liner. Trim neatly around the top of the hole.

Before spreading a liner in a pond, stream or rill, lay it out on the ground for 20-30 minutes to let it soften in the sun.

Position the butyl liner loosely over the hole so that the centre touches the base, leaving an overlap on all sides. You may need to get into the pond (remember to take your shoes or boots off first) so you can fit the liner into the shape.

Filling the Pond

Once the liner is roughly positioned, hold the edge of the liner in place with bricks or coping stone, and then slowly fill the pond with water. The water will help stretch and sink the liner so that it moulds itself to the outline of the pool. As the water pushes down on the liner, lift the stones or bricks so the liner does not stretch; you may need to pull the edges of the liner to make sure that it is straight and eliminate creases.

When the pond is full, check once again that the rim is level. Add or remove soil if necessary.

Finishing the Edge

Trim off any excess liner, leaving an overlap of about 15cm (6in). This will be covered by an edge of coping stones or turf. Coping should be laid with an overhang of about 5 cm (2 in) so that the liner is hidden from view. If you intend to have a submersible pump in your pond, lay a piece of plastic pipe under the coping to take the cable.

If you are bedding the stones in mortar, make sure that you do not drop any mortar into the pool; otherwise you will have to empty the pond and refill it.