Building a concrete pond is hard work, but well worth the effort.

The concrete.

To calculate the amount needed for your concrete pond, add together the area of the sides and the base, and multiply by the required thickness.

As the concrete should all be laid at the same time, do not under estimate the amount you will need. It is better to have to much than run out before you’re finished.

The concrete mix should be:-

1 part cement.
2 parts sand.
4 parts gravel.

If using ballast (sharp sand and gravel premixed) the mix should be:-

1 part cement.
6 parts ballast.

The concrete should be mixed so that it can be trowelled easily, but care should be taken so as not to make it to wet, or it will slump of the sides. All mixes of concrete must be accurately measured to obtain consistency across the pond. Use of a concrete mixer is recommended.

Premixed concrete is not recommended unless you are experienced in laying concrete.

A concrete pond must be laid in one piece. The bigger the pond the harder it is to lay in one. Please keep this in mind when designing your pond.

Tools and other materials.

The tools you need will depend on the method you use to build your concrete pond. The things you will need:-

Wooden stakes.
Hammer and/or mallet.
Straight edge.
Spirit level.
Spade and shovel.
Wire mesh 2” (5cm).
Builders sand.
Plasterers float.
Concrete mixer.
Builders bucket.
Waterproof gloves.
Polythene sheet.

The things you may need:-

3”(7.5cm) x 2”(5cm) sawn timber.
Shuttering ply.
Nails.
4”(10cm) concrete blocks.
Tamper (a piece of scaffold plank cut to length is ideal).
Brick laying tools (trowel, bolster, string line, etc).

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Setting out.

Once the pond shape is decided and the site levelled, mark the pond excavation, (pond size and shape + 6” or 15cm). Hammer in the wooden stakes outside the marked excavation. Level across the tops of the stakes using a straight edge and spirit level. This will make it easier to check the depth and level at any point of the excavation.

Method one.

For a concrete pond with sloping sides. Excavate the pond remembering to include level planting shelves where required, and to allow for the thickness of the concrete 6” (15cm). The angle of the sides should be no more than 70 degrees, or the wet concrete will slump to the bottom of the pond. The smaller the angle, the easier it is to concrete the pond. 30 to 45 degrees being the easiest.

Cover all surfaces of the excavation with wire mesh. This is used as reinforcing.

Using a plasterers float, trowel the concrete over the excavation to a depth of 2 to 3 inches (5 to 7.5cm). Cover with wire mesh and push into the wet concrete. Trowel on a further 2 to 3” (5 to 7.5cm) of concrete. Key the surface of the concrete by scoring it lightly with the edge of the trowel. Cover with a polythene sheet and leave for a couple of days to harden. The polythene sheet will sweat, keeping the concrete damp. This will stop the concrete drying to quickly and make applying the render coat easier.

Using a 3 sand to 1 cement mortar mix with added waterproofer, apply a render coat to the concrete pond approximately 0.5” (1.5cm) thick and leave to dry. Once dry, apply a coat of sealer or pond paint to the pond to prevent toxins from the cement leaching into the concrete pond water.

Finish by edging the concrete pond with the material of your choice.

Method two.

This is for concrete ponds with vertical sides. Excavate the pond without planting shelves to the required size, plus 6” (15cm), to the width and length and 10” (25cm) to the depth. Lay 4” (10cm) of hardcore in the bottom of the excavation and compact well. Line the sides of the excavation with wire mesh.

Construct a former to the internal dimensions of the pond, using timber and shuttering ply. Wet concrete is very heavy, so the former must be strong and well braced. Lengths of timber longer than the width of the excavation should be fixed to the top of the former at each end. These can be used to help keep the former in place by anchoring with stakes or with weights. They are also useful for lifting the former. Consideration should be given to the weight of the former as it will need to be lifted into the excavation.

Lay 6” (15cm) of concrete with waterproofer added to form the base of the pond. Tamp down well, ensuring that the base is level. Lift the former into place on the wet concrete pond base and anchor down. Pour concrete with waterproofer added into the space between the sides of the excavation and the former. Vibrating the sides of the former lightly with a hammer or mallet will compact the sides leaving a smoother finish.

When the concrete has hardened, dismantle and remove the former. The sides should be smooth, if not, a 0.5” (1.5cm) render coat should be applied. Let the concrete dry and construct the required planting shelves with blocks or concrete. Apply a coat of sealer or pond paint to all surfaces. Finish the pond edge with chosen materials.

Method three.

This is an alternative method for a concrete pond with vertical sides. Excavate the pond to the required dimensions plus 8” (20cm) to the width and length and 10” (25cm) to the depth. Lay 4” (10cm) of hardcore in the bottom of the excavation and compact it well.

Lay 6” (15cm) of concrete with waterproofer added to form the base of the concrete pond and tamp down well, ensuring that the base is level. Cover with a plastic sheet and leave to harden.

Build the sides to the required dimensions using 4” (10cm) thick concrete blocks and mortar. This should leave a gap of 4” (10cm) between the sides of the pond and the sides of the excavation.

When the block work has dried, fill the gap between the pond sides and the excavation with concrete and compact well. If the pond sides have been raised above ground level, or planting around the pond is required, the concrete can stop 12” (30cm) below ground and soil used to finish back filling.

Apply a 0.5” (1.5cm) render coat with waterproofer added to the internal block work. Allow to dry, and then construct the planting shelves with concrete blocks and apply a coat of sealer or pond paint to all surfaces. Finish the concrete pond edge with chosen materials.

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