Choosing the Lining for your Garden Pond
For the home builder, there are four main types of liner for you to choose from. They are a natural clay pond, a pre-formed plastic liner, concrete, and flexible butyl / pvc liner. Of these, the natural clay pond requires specialist knowledge, which I don't have, so it will not be covered here. Of the other three, your decision will largely be dictated by the type of pond that you wish to have. Each type has its merits and, hopefully, this page will help you with your decision.
Without doubt, most people think that this is the easiest type of liner to use. It may be made of plastic, butyl or fibre glass. You simply dig a hole, put in the liner and fill it with water. If only it were that easy. First, unless you are lucky, the shapes that are available to you at the garden centres will require a compromise on your chosen plan. Secondly, for what they are, I think that they are very, very expensive. However, its not all negative; these types of ponds are the easiest to maintain.
If this is the type of pond that you choose, mark out the shape on the ground and dig out the hole. Take care to get the shape as accurate as possible and don't just dig out a big hole and drop in the liner. The biggest problem that I have had with these is that they are difficult to get level once filled with water. This process can take some time but its not worth compromising. Once you have created your hole and tested that the liner is level, try to rock it and move it from side to side. Then lift out the liner and look for smooth areas in the earth. They indicate the points of contact between the earth and the liner.
By either adding earth to areas or removing it, the idea is to get to the situation where the liner makes full contact with the base of the hole. The reason for that is that the liner is relatively rigid and it will be supporting a huge weight of water which could result in cracking the liner if its not properly supported. It will also prevent the pond tilting when the water is put in.
Once you are happy that your pond is level and fully supported, remove the liner and cover the base of the hole and the sides with about 5cm of sand. Then carry out the same process as above. At the end of this phase, you should have a liner that is level and with a fully supported base. If the liner has shelves, the process for them is the same.
Now you need to think about the edges of the liner. The edge is not strong enough to take the weight of people, so if you intend to have a patio right up to the edge of your pond, the liner will need to be supported from below before you can build your patio. Failure to do this properly can result in a crack in the liner which will get progressively worse and you will lose your water, and thence your fish. Probably the esiest way to achieve the required support is to dig out about 10 to 15 cm of earth from under the edge of the liner that needs to be supported and to replace it with concrete. Once that has dried, it should be ok to lay your patio directly onto the edge of the liner. Always place your patio slabs into position and ensure that they do not have a tendency to tip into the pond before you try to cement them into place. The cement is there to secure them, not to prevent them from falling in.Top
Until relatively recently, concrete was the only suitable material for making garden ponds and, if it is used correctly, concrete is still considered by many to be the best material to use. Once it has fully set, concrete is unlikely to suffer damage from penetration of rocks or bird beaks and claws. However, whilst it can be moulded to virtually any shape, it is really only suitable for more formal ponds or large informal ones with gently curving sides as it is difficult to maintain a uniform thickness if the shape is too random.
This type of pond shouldn't be confused with a formal brick lined pond which is covered later.
Once you have dug out your hole, the sides, base and any shelves need to be very firmly tamped down and made as smooth as possible. Then the hole should be lined with builders' heavy-duty plastic. It is now ready for the concrete. The ideal mix for the concrete is 1 : 2 : 3 by volume of Ordinary Portland cement, sharp sand and fine aggregate respectively. Unless you are making a very small pond don't attempt this without using a cement mixer. They are quite cheap to hire these days and as well as saving a lot of effort, it ensures a consistency in the mix. (I find that an old washing-up bowl is a good measure as the smaller mixers that the hire shops have will comfortably take 6 bowls of material and mix it well.)
The concrete needs to be poured into the base first. A depth of 4" or 10cms is needed. Then the sides need to be covered to the same thickness. From this you can appreciate that either the sides need to slope quite considerably to prevent the mix from sliding down into the base (A minimum slope of 20 to 30 degrees is needed. Make sure that the join between the sides and the base is good.) or you'll need to form some wooden shuttering to hold the cement in place until it is set. That's the end of the first layer. Top
The water that the pond will hold is very heavy. (A cubic metre of water weighs 1 tonne.) So, the concrete needs to be reinforced. Once the concrete is dry, usually after about 2 or 3 days, line the whole pond with galvanised metal mesh. Then you need another layer of concrete. The mix is the same but the thickness only needs to be 2" or 5cm. The finished surface should be trowelled to a smooth finish. The pond must then be left until it is fully set. (Usually about a week since the chemical setting process continues for some time after it is physically dry.)
The finished surface needs to be sealed to prevent the chemicals in the concrete leeching into the pond and harming the fish. Any proprietary pond sealer from water garden centres will be OK providing you follow the instructions correctly. Top
The flexible liner can be made from plastic or pvc, but the best is butyl but there are some really good alternatives coming onto the market and a lot depends on how much you are prepared to pay. The choice has to be a personal thing and I suggest that you discuss the merits of each type with your supplier before buying. However, don't be conned into spending a lot of money just to get an extra few years of life. If you build the pond properly and do not have any of the liner exposed to direct sunlight, the liner will all last as long as you need.
As the name suggests, this is the most flexible way to build a pond. It is the most forgiving and is the only one that enables you to rectify any mistakes that you find without having to rip out all your work and start again. It also enables you to try a number of different approaches to any given design without causing any damage to the end result. Providing you are reasonably careful, you can alter the design of your pond, within the limits of the original size of the liner, before you commit to the final design. For these reasons, it is my preferred way to create a pond and the ponds in the pictures in this site were all made that way.
With the preformed rigid liner and the concrete liner, once you have made your design and built your pond, you are stuck with it. As I noted in the preformed liner part, those liners can tilt slightly unless they are really well settled before they are filled and if they do, there will always be more liner visible at one side of the pond than the other, and it will be a continuous source of frustration. Whereas, with the flexible liner, if you find that one side is slightly lower once the pond is filled, that side can easily be built up to the correct level afterwards.
Obviously, the initial task of digging out the hole for your pond is exactly the same as for the previous methods. However, although the flexible liner is reasonably robust, you have to be careful not to puncture it. To that end, it is important that you do all that you can to remove any sharp stones or other objects from the hole and to get the base and the sides as smooth as possible before the next step. One advantage of using flexible liners is that the sides of pond can be much steeper than would be possible for concrete ponds. Unfortunately, that usually precludes the use of sand to line the sides of the hole.
Over many years, you might be surprised to know that I have found that the best material for lining pond holes prior to using a flexible liner is ordinary newspaper and household carpet. Once the hole is a smooth as you can get it, line it with several sheets of newspaper. Slightly wetting the paper will help it to stick in place and I have found many sharp objects that I would otherwise have missed as I smoothed the damp paper into the hole. Then once the pond is completely lined with the paper, line it with pieces of old carpet or underlay. (Make sure that the lady of the house hasn't left any pins or needles in the carpet fibres or any old christmas tree needles. The only way to do that is to lay it out and go over it by hand. You will soon know if there are any needles to be found, but the odd prick of your finger at this stage is better than finding out once the water is in the pond.) If you haven't got any old carpet in your loft, try loitering at your nearest recycling centre and rescuing other peoples carpets before they get discarded. You could also ask any carpet fitting shop as they usually have old carpets to dispose of. Ensure you check for needles etc. The whole idea here is to provide a barrier between the earth and the liner for two reasons.
Firstly, water is constantly moving and anything sharp that comes into contact will eventually work its way through the liner, sometimes even years later. Secondly, as the roots of the plants around the pond grow, they will be deflected away from the liner by the carpet. This simple approach is extremely cost effective and I have had total success with it. Although the carpet will rot over the years, it will have done its job and if you were to lift your liner after 10 years or so, you would find a fine mesh of roots providing the same protection from the earth that the carpet did when the pond was new.
Once the hole has been fully lined with carpet, check again that no small bits of grit etc have managed to get onto the carpet and then the liner is spread out evenly over the hole. The pond books will tell you that as you feed water into the liner, the weight of the water gradually pulls the liner down into the pond. However, I have found more success if I get into the pond and do as much as I can to arrange the liner as neatly as possible before I put any water in. To do this, you need to be in bare feet to avoid danage to the liner and also don't gorget to check your knees for embedded grit. If its a bright sunny day, beware that the liner will heat up extremely quickly so have a spray hose handy to cool it off or you could burn your feet (it hurts a lot).
Once you have done what you can to arrange the liner into the pond, you can start to fill the pond. As the liner is pulled into the hole, it is important to remove as many creases as possible so that the end effect is of a smooth appearance. That is best done by pulling the liner into folds and allowing water pressure to keep them flat. Try to create the folds so that they point away from your usual viewing point so that they will be less obvious in the finished pond.
When the pond is completely full, the liner is tidied up and the edges fixed. In this case, the far side of the pond was edged with rocks and the near side was just finished of with some cement to seal the edge. The near side was then finished off by digging a small flower border along the edge. The few stone pieces provide somewhere to stand whilst carrying out routine maintenance. Top
There are times when you will want to create a pond that comes above ground level. For instance, to prevent the young or the infirm from falling in, or to make it easier for less fit people to maintain. Or it may be that you want to have a deep pond but don't want to have to dig out too much earth. In these circumstances, you might like to consider building a pond from bricks or blocks. Most people who keep Koi have a half and half set up where they dig out to a certain depth and then brick up to around a metre in height. That provides for the ideal depth required for the fish and it also means that it is easier to build in the filtration systems that have to accompany koi.
This type of pond is invariably a formal, uniform shape and is often made of decorative blocks that blend with other hard features within the garden. Without doubt, unless you are an accomplished brick layer, this is a job for the experts. However, the principles remain the same. Once the basic shape of the pond has been constructed, it must be lined to make it water tight. Semi-rigid linings can be made to order by specialist firms, or flexible liners can be used. Simply allow the pond to fill and trim the lining to fit under the top layer of the wall. The wall could also be sealed with a waterproof plaster. Before contemplating this type of pond, seek specialist advice from a water garden centre regarding the filtration required.
Other than viewing completed ponds, I don't yet have any experience in this type of work so I don't intend to provide any more advice. Top