Installing a garden pond liner

The method of installing a pond liner is identical for all materials except polythene. This needs shaping to the excavation before water is added, as it offers little or no flexibility. All other liners are malleable and use the weight of the water to mould them to the contours of the excavation.

DIGGING THE HOLE

The excavation for a pond liner should be the same size as the final pond, with a small allowance being made for a protective fabric or sand underlay. Complete accuracy will be difficult to achieve when digging, but this is not usually necessary.

The most important requirement when digging is to ensure that the walls of the excavation remain solid. It is almost impossible to replace any soil that has been dug out in error so that it will provide solid support for the liner. The hole should be dug in the soil in almost the same manner as one might cut cheese, making very definite lines that allow solid compacted soil to remain.

The best way to do this is to excavate the whole area of the pond to the level of the marginal shelves. Mark out the shape of the deeper part on the floor of this excavation, then dig down again. If there is a further deeper level, repeat the process. This ensures that the hole is accurately produced with a solid base and walls that will remain firmly in place when the liner is installed and water added.

Another important aspect is being sure that the levels are correct. Before beginning to dig, drive a peg into the soil as a prime datum from which to work. At strategic points around the pond shape, drive in additional pegs, ensuring that their tops are level with the first. To do this, lay a wooden board on edge across their tops and set a spirit level on top of it. This will give you an idea of whether the ground itself is level and provide reference points from which to measure down to the various levels of the pond. It is important that the edge of the excavation is level all around, otherwise there is a possibility of unsightly pond liner showing when the pond has been completed.

PUTTING IN THE LINER

It is always surprising just how much liner is required for even a small hole and, irrespective of the material being used, how heavy it is. For the most part, the successful installation of a pond liner is a job for two people.

No matter how tough the material being used, all liners benefit from some cushioning to protect them from the imperfections of the hole. Builders’ sand and specially manufactured protective fleece are widely used for this purpose.

Fleece makes a good cushioning layer once all sharp stones have been removed. However, it is not the easiest material to install, often taking as much effort to get right as the liner itself, and in some cases, its imperfections will show through. Builders’ sand is much easier to use, for although very fine, once dampened it is extremely versatile. However, it cannot be used where the sides of the hole are vertical, since it will not remain in place. If sand is the option, dampen it sufficiently so that it can be applied in the same manner as plaster, using a plasterer’s trowel. If you do not have such a trowel, it can be applied just as easily by hand, but make sure you wear heavy-duty gardening gloves. Smooth the sand over all the walls, the shelves and the floor, then put the liner in place while it is still damp.

Spread the liner across the excavation, weighing down the edges with rocks or bricks, then run water into the centre so that it moulds to the contours of the hole. The weights around the edge can be removed gradually as the liner forms to the shape. Take great care when lining an irregularly-shaped pond to ensure that the liner is positioned correctly before adding water. There is little more frustrating than finding an excess of liner at one end and a shortage at the other when the pond is half full of water. Once the water begins to run into the liner, it is not just a matter of sitting back and waiting for the pond to take shape. This can be a time of quite frantic activity, since all the wrinkles will need smoothing out as the weight of water increases. Do not forget that if things begin to go wrong, you can always shut off the water supply. So many people fight against the increasing weight of water without considering that they could stop the flow. Rather than create a multiplicity of folds, it is preferable to make only a few bold ones. These will be much more effective and easily disguised.

Once the pond has been filled to the required level, and you are happy that the liner is satisfactorily in place, trim off the surplus around the edges. However, remember to leave enough for securing to the ground with your chosen edging.

INSTALLING A GARDEN POND LINER

1 Mark out the desired shape of the pond using pegs, making sure their tops are level, then dig out the whole area to the depth of the marginal shelves. Check all levels with a spirit level.

2 Mark out the shape of the deeper level of the pond on this excavation and dig out. Remember to check levels. If the pond is to contain a further deeper level, you can repeat this process.

3 Builders’ sand is the easiest material to use as a protective underlay for the liner. Dampen the sand slightly to make it more manageable and spread it over the base and sides of the excavation.

4 Put the liner in place while the sand underlay is still damp; you will probably need help even for a small pond. Spread it over the whole area, weighing down the edges with bricks or rocks.

5 Run the water into the centre of the pond so that the liner moulds to the contours of the hole. Wrinkles in the liner will need smoothing out as the weight of the water increases.

6 Once the pond has been filled to the required level, trim off the surplus liner around the edges. Remember to leave enough for securing to the ground with your chosen edging material.