Concrete Pond Construction

Q. I am in the process of building a pond ( with a butyl liner ) 18 x10 x 4-6" in your construction pages you mention the liner section, but unfortunately when you talk about skimmers etc. or any other pipe work entering the pond from the side no mention of how to achieve this with the use of a liner except for the bottom drain.
Can you please advise me how to do this, or must everything apart from the drain come from the top?

A. There is a limit to how much I can include in the web pages, and as nobody in our club has used a liner recently I do not have any photos of this.
As with the bottom drain the skimmer is not a problem. They are supplied for swimming pools and are available either for fitting in concrete walls or for use with liners. When you purchase the skimmer you must state that it is for a liner, and it will come with a fixing plate and screws. This is then attached to the liner in the same way as with the bottom drain using silicon compound.
It is also quite easy to get pipe outlets which work in the same way, and are available in the usual sizes from 1.5 inches to 6 inches. They should be available from most specialist koi dealers.

Q. When using a pond liner and you have to cut various holes in it for the bottom drain, filter input and outlet pipes. What do you use to make sure the area around the drain and pipes does not leak.

A. The bottom drains that you purchase for use with a liner has a ring around the top which fits on top of the liner and is then secured to the bottom drain with screws which are supplied. In other words the liner is sandwiched between the plate and the top ring of the bottom drain. It is also necessary to use mastic to seal between these faces. When you purchase the bottom drain they should be able to also supply the correct mastic. The smaller pipes for the pump returns etc are connected using tank connectors. These have a screwed end and two collars. The pipe part passes through the hole in the liner, and one collar is then on either side of the liner. The liner is then sandwiched between the two collars. Again mastic should be used. The cheapest and best way to purchase many of these components in the UK is to attend one of the koi shows which are held around the country. The dealers usually sell this hardware at a discount price.

Q. Will putting say polystyrene under the liner help save heat or does below ground retain heat anyway?

A. Polystyrene sheeting is a good idea to conserve the heat, but I would only use it between a solid wall and the liner. Check out this photo.

Many koi-keepers now use Polyurethane (PU) sheet foam now to line the pond (sometimes the base too). It can be fibre glassed over too in many cases. It has the advantage of being able to be cut, chamfered and sanded accurately (eg around skimmers, drains etc) as it has a denser more robust structure.

Q. I intend to lay a concrete floor (4-6ins) to hold the drains and also fit a collar around the edge to take the above ground wall. I then want to fit a .75 butyl or 1mm true rubber liner to the excavation. Does this sound reasonable? is the butyl or thicker rubber better. Are there any pitfalls that you might know of?

A. The concrete floor should be at least six inches deep with reinforcing. In the way of the bottom drains and the pipes you will need to dig out a trench so that there is sufficient concrete underneath. See the 5th photo of building Louis pond. By the way this pond is 18 x 12 x 6ft and holds 8,200 gallons, and it has three drains.
For a pond that is more than 4ft deep I would not even consider that method of construction as there is a very great danger of the walls caving in if there is very heavy rain. I know of a couple of ponds where that has happened after several years.
Butyl rubber was the favourite some years ago, but it is now not so easy to get and there are other types of rubber on the market which are equally as good. Always go for a good quality one and not the cheapest as this is a recipe for disaster.

Q. What is a cement collar?

A. A concrete collar can be seen on Steve's pond . This is used when you intend to fit a liner without using a concrete block wall.