We offer a full pond construction service (Click Here). If you want to construct your pond yourself this advice sheet describes the different types of pond liners available.
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Choosing the correct pond liner for your pond construction project is crucial if it is to last. The best pond liners can last for thirty years or more. Choose the worst and your pond might be leaking and in need of a new liner in as little as seven years. Replacing the pond liner will often mean dismantling the whole pond and starting again from scratch. Usually everything that is sitting on top of the pond liner will need to be taken away before it can be removed and a new one put in its place. This will often mean that things like paving, rock gardens, waterfalls etc. must be taken up first. The cost of replacing the liner is a small consideration against the huge cost and disruption of dismantling and replacing most of the water garden. All of this can be avoided at the beginning by buying the right pond liner.
Until fairly recently this has been the best pond liner you could buy from a high street pond shop. Butyl has been around for something like 30-40 years. I have worked on ponds of this age still with their original liner. They remain flexible and remarkable unchanged for all of their long life. It is so durable and stable that once a butyl liner is about a year old and it no longer has a perfect clean surface it is very difficult to make an informed judgement about its age solely from its appearance.
Butyl can be be box welded. This is the name used for made to measure pond liners that are cut and bonded together to fit the shape of your pond. This can only be done for rectangular ponds and the manufacturers will only supply box welded pond liners containing perfectly rectangular panels. If your pond is not as rectangular as you think it is, a box welded liner might not be suitable. Smaller irregularities can be accommodated if you make each panel match the longest side. Box welded liners carry a much shorter guarantee. The material is still as good. The reduction in the guarantee is to do with the joining mastic. I have been assured that these liners are likely to last as long as one without joins but nonetheless the guarantee period is much shorter.
Insect damage. There is an aquatic insect that produces larvae that will eat butyl pond liner. It is uncommon ( I have seen the effect of this on only one pond) and I believe that it is only found in Surrey and possibly Kent. EPDM which is very nearly the same as butyl with almost identical properties, seems to be immune from this insect.
As with all pond liners they are not completely indestructible. They are not very resistant to sharp edges. So make sure that there are no sharp objects in the pond. This includes sharp stones and gravel (drive gravel is commonly used to cover the soil in aquatic planting baskets. It is unsuitable for this purpose and it puts the liner at risk.) Ponds containing sharp stones or other objects are at their most dangerous during maintenance work. A sharp object such as a stone or piece of glass will probably not cut the liner if it is left undisturbed at the bottom of the pond. If someone steps on it while they are in the pond carrying out maintenance work then this is when harm is most likely to occur. Sharp tools must also be carefully used so as not to bring the blade into contact with the pond liner. Knives, scissors and garden forks are the tools most likely to be used in the pond, usually to divide overgrown plants. It is best not to let the plants get so overgrown that sharp tools and excessive force are needed.
A herons beak can also be the cause of liner damage. A herons beak will usually only damage the liner where there is very shallow water or a long shallow sloping pond edge. The heron will make quick stabbing motions with his beak in an effort to catch your fish. If the beak is stabbing down into deep water or close to steeply sloping pond sides it is very unlikely that it will come into contact with the pond liner.
Sometimes an animal will damage the liner with its teeth or claws. This might be because it has fallen into the pond and the liner has been ripped by its efforts to get out. This is rare and there is not much that you can do to protect yourself from this. Sometimes the water level in the pond is very low, either because the pond hasn't been topped up in a long time, or because the pond is leaking. Animals that drink from the pond will step onto the liner if they need to, to reach the waters edge. They will often use there claws to achieve a firm foothold, especially on a slope. If your water level is low, top it up or repair the pond quickly. Don't leave the water level low for an extended period. Foxes are now common visitors even to urban gardens.
Most tree and plant roots will not puncture the pond liner but will instead grow around it. I think that this is because of the way that plant roots grow. Large roots don't usually grow outwards from the plants at full size. Instead small or even micro roots grow and then thicken into large roots. If the tiny new root meets the pond liner it will usually be deflected. When I have removed old pond liners it is common to find a great web of tree roots harmlessly growing under and around the pond liner. If the pond is very old some of these roots can show through the pond liner as thick ridges resembling power cables or pipes.
However, some plants pose a very real threat to the pond liner. Bamboo is the worst. It cut through pond liner as if is wasn't there and very soon there will be lots of shoots coming through. Other plants such as willow and dogwood can also perforate pond liner. Some grasses will harm the liner others will not. Some large grasses are harmless and some very minor looking grasses will tear through easily making lots of tiny close set holes. Holes made by roots often don't cause the pond to leak very much in the early stages. This is because each hole is blocked by the root that made it. It is much like a tire with a nail in it. The air only comes out slowly until someone takes the nail out and then the air comes out all in a rush.
This is a very similar product to butyl pond liner. It is similar in its appearance and its properties. It is strong and durable and will last decades if treated with respect. It is cheaper than butyl. At the time of writing butyl is very expensive and for this reason virtually unobtainable. Suppliers are selling EPDM instead.
EPDM can be be box welded. This is the name used for made to measure pond liners that are cut and bonded together to fit the shape of your pond. This can only be done for rectangular ponds and the manufacturers will only supply box welded pond liners containing perfectly rectangular panels. If your pond is not as rectangular as you think it is, a box welded liner might not be suitable. Smaller irregularities can be accommodated if you make each panel match the longest side. Box welded liners carry a much shorter guarantee. The material is still as good. The reduction in the guarantee is to do with the joining mastic. I have been assured that these liners are likely to last as long as one without joins but nonetheless the guarantee period is much shorter.
Firestone is another very good pond liner. It is made using latex. It has not been around as long as butyl. I don't remember it being available until the mid 1990's. It has not been around long enough to prove that it is as good as butyl but is is widely regarded as being a very good pond liner of comparable quality. It is thicker and heavier than butyl which does not prove that it is better but its heaviness is reassuring. I have used this material a great deal and I have been very impressed.
Firestone pond liner cannot be box welded.
PVC pond liner is a little cheaper than the others. It is however a greatly inferior material. I have commonly seen leaking ponds with a PVC pond liner as little as seven years old. These liners come with impressive guarantees of 20 years or more. If you are unwise enough to buy a PVC pond liner and find in due course that your pond leaks, you will find that the guarantee is probably not going to provide you with the cover that you might expect. PVC pond liners are covered by a manufacturers guarantee with exclusions. If you can prove that your pond liner has failed through faulty manufacture then your guarantee will be valid and you be able to make a claim. You cannot make a claim if the pond liner has degraded through exposure to sunlight (which is of course the main reason that PVC liners fail).
PVC is damaged by the ultra violet light contained in sunlight. The high energy rays of ultra violet smash the PVC polymers. The PVC loses its plasticity and flexibility. It becomes hard, rigid and brittle. Of course holes can be repaired. You don't have to throw away your PVC pond liner the first time it leaks. PVC pond liners can be patched and when further holes come along these can be patched too. A PVC pond liner can often be kept going for many years after its first leak. Still you have to completely empty the pond each time and find and patch all the holes. It is a lot of trouble to go to that can be avoided by not buying a PVC pond liner.
Patches can only be applied successfully to a clean flat surface. If the hole is on a fold or wrinkle, the fold must be flatted out before you can patch it. This can be difficult. PVC becomes rigid with age. If you try to flatten out the fold on an old PVC pond liner, the fold may split or crumble. Butyl doesn't become rigid with age and so patching a hole on a fold is much easier for this material.
Some PVC liner will become porous. This means that after any holes that it has have been found and repaired the liner still continues to leak. The water soaks directly through the pond liner sheet and into the ground behind the liner. This can happen to any PVC pond but it is true that deep water makes the problem worse. The greater the pressure of water in the pond the more easily the water will go through the liner. As the pond loses water and the level goes down the pressure of the water will fall. If the leak is due to the liner becoming porous, the water level may eventually reach a point that the pressure is reduced so that it is no longer enough for the water to be pushed through the liner. The water level drops until it reaches this point and then stops going down. It can look as if there is a hole and the water level has stopped when the water level reached the hole. When the pond is drained, no hole can be found at the level where the leak stopped. I know of no certain way of curing this problem. You will most likely need to change the pond liner.
I cannot recommend PVC for its use in constructing ponds and water gardens. The money saved in the purchase price is small. The cost and disruption of replacing the liner and having to dismantle and rebuild paving, waterfalls, streams and rock gardens in order to change the liner is massively disproportionate to the saving.
There are some commercially available PVC liners that are many times thicker than the liner that you can buy in a typical pond shop. These seem to overcome by there great thickness and superior mix many of the problems that I have described here. However, I have only ever seen them on large scale commercial ponds, usually constructed as part of a large housing development.