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Fitting and Filling a Liner

By: Dr Gareth Evans - Updated: 24 Oct 2019 | comments*Discuss
Flexible Liner Pre-formed Liner Moulding

Fitting the liner is the moment when the pond is born; before this all you really have is a hole in the ground; after it, you have something which will hold water – with all the future promise that entails. Like all births, things can go wrong – so it is worth taking a bit of care at this stage to make sure the new pond gets the best chance of a long and useful life.

Whether you have chosen a pre-formed or a flexible liner for your pond, the initial stages after the excavation are essentially the same. Having finished digging your hole – going an inch or two further than the intended depth of the final pond – the next step is a final check for any sharp stones or other objects which might damage the liner or moulding. Once these have been removed, a protective layer needs to be applied to make sure that nothing will harm the pond structure.

Traditionally, this has been a thick layer of sand or wet newspapers, some two or three inches thick, but recently, purpose made geo-membranes – once the preserve of landscaping professionals – have become cheap enough to be used for domestic ponds too. Most good liner stockists sell these cushioning geo-textiles also, which are really best suited for use under flexible liners, since a sand layer is better at bedding in a pre-formed pond. If you are fitting a pre-formed liner, now is a good time to make a rough check of the fit and then one final check that the top surfaces are level.

The Flexible Liner

For anything other than the smallest of ponds, this is the one part of the proceeding where the pond-builder is well advised to recruit an extra pair of hands if at all possible – and trying to pick a day without too much wind is a good idea too!

The first step is to begin gently fitting the liner into the hole, folding the material so that it lies properly within the excavation. There is often a tendency for a lot of little folds to appear as this process continues – which should be gradually worked along the hole, starting at the bottom, to form a smaller number of larger pleats. Some heavy stones laid around the liner edge will help hold everything in place and stop it sliding down into the excavation.

Once the liner is laid to your satisfaction, it is time to fill the pond. Place a hose in the pond, anchoring it at the bottom with a heavy flat stone. As the weight of water increases, the liner will be flattened against the walls; continue to smooth the sides as best you can, folding and tucking in any excess – but avoiding any urge to trim the liner material until the pond is finally full.

The Pre-Formed Liner

The key to fitting a pre-formed pond liner is in making the excavated hole as close a match to the contours of the moulding as you can – allowing the protective sand layer to make up any discrepancies and finally adjust the level. A certain amount of back-filling is to be expected, but too much should be avoided if possible as soil tends to become compacted over time – which could lead to shrinkage and a lack of support for the fabric of the pond – so it is far better to dig the hole accurately in the first place. Once the moulding is positioned properly, it too can be filled with water, which can sometimes cause a little bit of movement in some of the semi-rigid types, so it is a good idea to start off slowly and keep checking the level as filling progresses.

With the pond lined and filled, all that remains is to edge it – and then be patient while the water chemistry settles down. While you are waiting, however, there is always the lighting, fountain or waterfall to install, not to mention mulling over which plants and fish you plan on adding – so the time does not have to be wasted!

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Hi We had a new butyl lined pond created in our garden approx three years ago.It would be great if it didn’t leak! We had pebbles put on top of the liner of our new pond to protect it from the heron and his pesky beak which would cause a leak every spring with our old pond.It worked.However, we didn’t factor in a new visitor to our pond, a rat.When we finally set to trying to fix the damage, we could see that the rat had made lace of the butyl liner above a concrete shelf, in other words it came in from under the butyl. We pulled back so much of the butyl in a clear clean line from one side of the pond to the other and the underlay, cut away the ruined underlay and butyl, cleaned it down, and then placed fresh underlay underneath.We then put new butyl right across well below the damage (18”), sticking it in place with a recommended butyl glue.Repositioned rocks and stone, filled and it’s drained again. If we’ve gone right across the pond and we’ll below the damage, why is it still draining? Thank you Pond Failure
Pond Failure - 24-Oct-19 @ 10:32 AM
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