Pond Liners – Rigid, Flexible, Butyl, UPVC

If you’ve ever been fortunate enough to visit the Lake District, or any other majestic inland water body, you would have witnessed the perfection that nature manages to effortlessly achieve without fail, in the design of her landscapes. She provides the model, against which we base our own pond designs. The hardest part of a pond building project is to reproduce in our own plot of land what we have in our mind’s eye – which is most likely to be based on what we have seen on our travels through the countryside. Our aim is to install a pond that looks as though nature would have placed it there – and one that has been there for as long as anyone can remember. The scale and characteristics of our pond-to-be will determine what route we take when choosing which material to use in its construction. We are able to make our pond any size or shape we desire, just like nature would have intended with all her resources to hand. With an artificial liner, we can site our pond anywhere in our garden, even above ground – to contrast what we find in nature. To achieve our goal, we must choose our pond building method wisely.

1. Why do I need to line my pond?

All natural water bodies occur where they do because of the natural geological conditions. We, however, want to bring water into our own garden, where if left to nature, would perhaps never host a pond. The underlying soil may be too permeable, or the lie of the land may not naturally collect water and we must intervene if we desire a pond in our garden.

2. I have a very heavy clay soil – Can I not build my pond using this?

Clay is in fact the perfect pond building material. It’s impermeable, east to work with (but difficult to dig!!) and is actually the soil-type of choice for koi and goldfish farms. A natural mud pond provides fish with many environmental benefits which produce fish in tip-top condition. However, a clay pond will also be a very murky pond, making one less than ideal for viewing your beautiful fish. One of the benefits of choosing a liner (rather than clay) is that you can achieve crystal clear water and make a watertight pond in any soil type – whether clay, loam or sand.

3. What are the options when considering a ‘lined’ pond?

There are two routes you can take : a. an off-the-shelf instant pond approach, or b. the no-holds-barred method for the more creative – a liner. There is obviously a market for both approaches but which is going to be the better one for you?

a. Preformed pools.
There are two or three different types of preformed pool available, offering us differing degrees of rigidity, lifetime expectancy and size. The most basic of preformed pools are made from a very flexible thin plastic that is moulded into various shapes, usually holding up to 70 gallons. Tougher high-density polythene pools offer improved strength and puncture resistance and although they are semi-rigid they are capable of holding nearly 200 gallons comfortably when buried. The most durable of the preformed pools are the rigid glass-fibre pools which are also the most popular. Available in a range of volumes from a tiny 30 gallons to over 1000 gallons, these strong and durable ponds are built to last a lifetime.

If you are also an indoor aquarist, you’ll be familiar with the limited choice when  choosing an aquarium, being limited to the range that our retailer can supply. The same can be true for preformed ponds. It is rare for an aquatic outlet to stock the full range and you might have to be prepared to wait a few days while your particular choice is ordered. Before looking at ponds, you will have a good idea of the area of the garden that you want to give over to water. This will immediately allow you to focus in on the preformed ponds that are the most appropriate for your plot. The models in your size range will offer different depths, and shelving arrangements for marginal plants, some of which may be more to your liking than others.
If you intend your pond to be a formal, regularly shaped pond then rigid fibreglass ponds offer you many benefits in that you do not have to dig a hole of the correct geometric shape or dimensions. Just make one large enough to take a pond, back-fill accordingly and hey-presto, you’ve created a perfect formal pond without using a set square or compass. If you have chosen a pond over 300 gallons in volume you will not be able to get it home in the boot of your car so make sure your retailer can deliver it when you want it (and hopefully free of charge).

4. I like the idea of buying a preformed pond – how easy are they to install?

Installing a rigid pond could not be more straightforward.

1. Dig a hole a little bigger than the shape and depth of the pond.
2. Place a loose covering of moist sand in the hole.
3. Place the pond in the hole, ensuring it is level and begin filling with a hosepipe.
4. As it fills, start to backfill with loose soil or more sand, checking regularly that it is level.
5. Keep the remaining spoil to one side with a view to using it to make a raised rockery and waterfall.

NB: Be prepared to see your pond appear to shrink as you position it in the ground. Once n the ground, they often look much smaller than they did when displayed against a wall in the garden centre.
b. Flexible pond liners.
Pond liners offer us flexibility in both the material we use and the extent to which we can design a pond. Long gone are the days when a heavy-duty polythene sheet was the method for lining a pond. Today’s pond liners have gone the way of pond pumps in that they have been re-engineered to meet (and indeed exceed) our expectations, with many pond liners now being sold with a lifetime guarantee (in excess of 25 years).

In a similar fashion to rigid ponds, flexible pond liners are available in a range of qualities that reflect their durability. Made from materials such as PVC, EPDM and butyl rubber and more recently hi-tech composite materials, which to be competitive, are guaranteed for life and as long as they’re installed correctly.
Liners are sold either pre-cut and packed or off-the-roll, depending on the size of the liner. Take your three-dimensional pond measurements to your retailer who will then work out the area of liner you require. This is also a good opportunity to plan out a waterfall. One particular advantage a liner has over a preformed pool is that you can lay the liner to incorporate a waterfall, making the cascade in effect an integrated extension to your pond. So even if your waterfall leaks (as is often the case) as if by magic, all of the leaking water still returns to the pond.

Once cut off the roll, your liner should easily fit into the boot if your car (but may be deceptively heavy). Because of a liner’s flexibility, more care must be taken when preparing your hole to protect against protruding stones or invasive roots. If the liner is going to last over 25 years, you cannot expect it to do so while pressing down hard against a sharp object.

5. What do I need to know before I can buy the correct sized liner for my pond?

Measure the dimensions of your pond (length x width x max depth) and you can then calculate the area of liner required.

For example:

To line a pond 8’ x 6’ x 3’ deep.

You will need a liner (8 + 3 + 3) x (6 + 3 + 3) in size. You then need to add a further 2’ to both width and length to accommodate sufficient overlap at the pond edges. So in total you would need a liner 16’ x 14’.

6. How do I lay the liner?

Prepare the shape and depth of the hole as desired (this time you’re the designer) and then cover the surfaces with loose damp sand or even special pond underlay. I have even used old carpet very successfully (but remember to check for any old tacks!). The liner will become very supple in direct sunlight making laying it far easier. Once you have laid the liner and attempted to reduce the number of creases, start filling the pond up, pulling and stretching the liner as it fills to reduce the creases further. Only when the pond is completely full should you trim off the excess liner, leaving at least nine inches overlap. Remember to leave an extensive overlap intact to underlay your waterfall.

7. How much will each method cost?

Price comparison.

How much would it cost?

1. 250 gallon pond

Rigid Fibreglass                   0.5mm PVC                         Butyl Rubber

‘Lifetime Guarantee’               ‘Lifetime Guarantee’               ‘Lifetime Guarantee’

8’ x 6’ x 2’ shelved                  13’ x 11’ equivalent                13’ x 11’ equivalent

+ irregularly shaped

£239.99                                  £43                                          £100

2. 1000 gallon pond

Rigid Fibreglass                   0.5mm PVC                         Butyl Rubber

‘Lifetime Guarantee’               ‘Lifetime Guarantee’               ‘Lifetime Guarantee’

16’ x 8’ x 2.5’ shelved             22’ x 14’ equivalent                22’ x 14’ equivalent

+ irregularly shaped

£1000                                     £84                                          £224

In summary, each method of creating a pond provides us with different benefits depending on the nature of the pond. Both materials now offer a similar guarantee, with pond liners giving more flexibility with our pond design. We dig our hole first and then line it. With rigid ponds, we work the other way round, digging the hole to suit the size of the pond. Flexible liners can prove difficult to install in a formal shape (square or circular) whereas preformed ponds can create that effect perfectly and immediately. The choice is yours but with flexible liners you’re offered far more scope as pond designer and comparatively, they offer excellent value for money.

Kill blanketweed and string algae.