N.Design Studio

 

A Guide to Modern Koi Pond Construction

Pond construction using a liner

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Building a liner pond 1.

First we will look at a liner pond. The simplest way and of course the cheapest is to dig a hole, put in a liner, and fill it up with water.

When this has been done then you should line the side of the trench that will be the pond wall with shuttering such as hardboard ensuring that it is well supported so that it will not bulge out when the concrete is poured in and tamped down. This shuttering must be level and you can then use it as the final level for your concrete. The concrete mix should be the standard mix of 3 parts gravel, 2 parts sand, and 1 part cement by volume. The mix should not be too wet, but wet enough so that you can tamp down the mix with a length of wood so that there are no air pockets remaining. This should then be left for 24 - 36 hours and the shuttering can then be carefully removed remembering that the concrete is not yet hard. The top corner over which the liner will be laid can now be smoothed off so it gives a radius instead of a very sharp edge. As the concrete can still be easily damaged it is better to leave it for a few days before starting to dig out the pond.

When you are satisfied that this is satisfactory you can now start the work of digging out the pond. This is a very heavy job especially as in the Cardiff area it is nearly all clay and if the pond is large it may well be worthwhile considering a small JCB type excavator. It is possible to hire a small one that will pass down the side of the house to the back garden.

When the digging is completed consideration must be given to the fitting of bottom drains. It is possible to dig a trench to fit the pipes and bottom drain and then fill it in, but the much more satisfactory way is to fill the trench with concrete so that the drain is not only securely held in place but will also support the liner when it is fitted in place around the drain.

It may be at this stage that you are considering building this type of pond without a drain to reduce the cost, but I am sure that in a few years time after regular siphoning out the pond you will regret the day that you did not fit bottom drains. So think carefully about this.

Before fitting the liner to the excavation it is necessary to ensure that there are no stones on the sides or on the bottom which will eventually pierce the liner with the wait of the filled liner. It is a good idea to line the whole inside of the excavation with old carpet or carpet underlay as this will protect the liner and also help to insulate it. This or similar material can often be picked up from the local disposal yard or from a skip.

Types of liner.

There are several types of liner on the market, but to ensure that the liner will last for many years it is worthwhile purchasing a butyl rubber liner with a long guarantee and from a reputable supplier. If possible find someone that has purchased one recently and they can probably offer advice.

Fitting the liner.

For this type of pond the liner will be supplied in one large sheet and so it will be necessary to get several willing helpers to lay it out over the top of the excavation. It is important to see that there is ample liner all around so that when it is finally in place and filled with water you have sufficient liner to turn it up into the surrounding wall and well above the pond water level. Some books do recommend that you let the weight of the water spread out the liner, but to ensure maximum life of the liner then it is better to get the liner into place and then as the water fills up to pull it carefully into place and folding it as required in the corners. It is better to have as many straight lines as possible when building the pond as this will then reduce the creases in the liner.

Comments.

This type of pond is often used when cost is a prime consideration and can be quite successful if used with in certain limits.

The main problem is the possibility of the side wall collapsing. Several things should be borne in mind when building this type of pond:-

a). The pond should not be too deep as this will give more chances of one or more of the walls collapsing. It would seem that 4' 6" deep at the side near the walls is near to the limit although you can have a deeper section in the centre of the pond.
b). The walls should not be straight but should be sloped again to prevent the walls collapsing.
c). It is essential that a concrete collar is used under the liner and if the pond is going to be fairly deep this must be of a good solid construction to prevent localised pressure on any part of the wall.
d). Great care must be taken if the pond is emptied or large amounts of water removed especially in very wet or dry conditions as there is a very good chance of the walls being weakened. When the pond is full or almost full the pressure of the water will support the walls.

Building a liner pond 2.

Many members wish to have a larger pond, with say a depth of six feet or more but are worried about the problems later on with cracks and leaks that can be associated with a rendered pond.
An ideal solution to this and probably the most popular with Koi-keepers is to build the pond using concrete blocks and then using a preshaped, or box liner, to fit inside.

The ideal and most expensive way is to build the pond as described in the next few pages for a concrete pond. It is however possible to use a much cheaper type of construction that falls between the building a hole in the ground and the full concrete pond. To do this the first thing to consider is the base. If possible it is better to build a full concrete base which will incorporate the bottom drains, and the foundations for the walls. This should be a minimum of 6" thick, but in actual practise in way of the drains and the trench for the pipes it will probably be 10" to 12" thick.
An alternative method is to build an excavation around the base of the pond which will act as a foundation for the walls. It is still advisable to concrete in the bottom drains and the necessary pipework to ensure it does not move in relation to the liner as described in Building a liner pond 1. If you do not wish to build the walls as described for a concrete pond then many members have used concrete blocks 18" x 9" x 4" standing on edge to build a 4 inch thick wall. It is advisable with this type of wall to back fill after completion with stone dust or preferably with concrete assuming that you have not left a big space between the excavation and the wall. The pond can then be measured and the liner ordered to fit exactly into position and this will ensure a minimum of folds in the liner.

TIP. If you are building close to the house or large boundary walls then you should get professional advice before starting the excavation to ensure that there will be no damage to the house foundations as you may well find that your house buildings insurance will not cover this.

Also check out Liners in Questions & Answers.
To view out construction pages for liner ponds check out Steve & Jan's pond and Mark's pond.

The construction of large concrete ponds is dealt with seperately, and can be found at Concrete pond construction