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There
are various types of liner to choose from including pre-formed, cut-to-fit and clay. Cut-to-fit liners are the most popular as they give you the freedom to make your wildlife pond your own shape, size
and depth.
Many garden centres sell pre-formed ponds, usually made of
plastic or fibre-glass, largely designed for housing ornamental
fish. These need to be carefully dug beforehand, but can last a
long time (many over twenty years). The downside is that there
is no room for creativity, and many pre-formed liner designs are
exclusively fish-friendly, lacking slopes for other wildlife to
get in and out. Some people choose to make raised up garden
ponds with troughs or raised pre-formed liners. Remember that
many forms of wildlife will find this much harder to get in and
out of.
The most popular and reliable liners are made from butyl (though
other materials are also available). This is a flexible
material and can be cut to fit, allowing you to be more creative
with shape and size. The disadvantage of using this type of liner is
that they are prone to punctures, often from sharp stones (plus
the occasional claw or beak) and degradation from sunlight. Don’t let this put you off though,
just be sure to add an extra protective layer underneath such as
old carpet and make sure the edges are covered with planting.
For this type of liner powdered bentonite clay is mixed with sand or
subsoil material and then laid directly over the soil with a
rake. It can be used in any size pond providing the sloping
sides are not too steep as this would cause the material to
slump. It's not too expensive and reasonably easy to install
(some effort is required to make sure it's mixed properly). Once
wet the material forms a watertight barrier. A layer of subsoil
can be laid on top to plant straight on to.
These liners consist of a membrane containing bentonite clay
mineral. It can be heavy and difficult to lay; large rolls will
need machinery to move. It comes in varying sized sheets, in
either prehydrated or dry form (the latter is slightly cheaper
but requires the application of granules along the joins). For
the liner to be watertight at least 300mm of compacted subsoil
needs to be spread evenly. Once wet the clay expands under
pressure to form an impermeable barrier. It's somewhat 'vandal
proof' as if punctured it can reseal itself. Slopes should not
be too steep to avoid slumping of the soil covering and liner;
you can plant directly into the soil covering. This is a good
option for medium and larger ponds, especially those in public
places.
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