With the advent of modern plastics, liner and pre-formed ponds have overtaken concrete as the preferred method for constructing ponds, each has its own merits and this comparison will enable you to make up your own mind.
They are straightforward to install but, as with any pond, the location should be away from hedges and trees so that leaves do not fall into the water. These will break down in the pond causing future problems.
You will also make sure that there is some shade during the day, as too much sunlight will cause problems such as green water suspended algae and blanket weed.
Have a plan in mind of what you want to achieve and outline the desired shape with rope or sand. Then you can start digging.
Create shelves at different depths to accommodate various types of aquatic plants, perhaps very shallow at 2ins, then 5 inches and wide enough to hold containers, and 18 inches. Overall depth should be at least 2 ft and 4 ft if you want to keep fish.
It might sound obvious but make sure that the liner you purchase is the correct size for the pond you are building. Measure the length, width and depth of the pond. Then, double the depth and add the length and width. Now add 2 feet for overlapping the pond edge. This will give you the correct size.
The hole must be level so use a spirit level balanced on a block of wood to check all around the sides. Remove any sharp stones or tree roots that may pierce the liner.
Now line the hole with a layer of sand or other material such as old carpet. If possible warm the liner in sunlight to make it more flexible and shape it into the hole, try to keep wrinkles to a minimum and add a little water to help settle it into place.
Slowly fill with water making sure the liner doesn’t stretch. Trim off any excess liner above the water line and use mortar to fix patio stones or similar around the pond edge to keep the liner in place.
Place the pond (the correct side up, not upside down) where it is to be positioned and mark out by drawing around the shape in the sand. Next measure the shelves. Then dig out the shape including the shelves but adding about 5cm to the depth to allow for a lining of sand.
Remove any stones or roots as they might pierce the liner. Then place the liner into the hole and adjust the shape if necessary, making sure it is level (use a spirit level balanced on a piece of wood across the width and length of the pond). Once you are satisfied the shape is correct, line the hole with the sand and return the pond and it should fit snugly.
When you are sure the pond is level, use sand to backfill and compact it to prevent the pond from moving as it is filled with water. However carefully installed there’s always a chance of some movement, so once filled, leave the pond for at least one week before adding edging stones, plants or other features.
First, the hole needs to be dug, about 6 inches below what will be the final depth, making sure that the levels, angles and sides are accurately measured - a formal pond needs to look exactly true.
Then dig a trench, about 4 inches deep by 8 inches across, around the sides at the base of the hole and fill this trench with concrete to provide foundations for the walls.
With the bottom of the hole level, add a layer of sand, compact it firmly adjacent to the wall foundations, and lay 3 inches of concrete. Allow to dry, then add some galvanised mesh and pour another 3 inches of concrete on top. Once the cement has dried use breeze blocks to form the walls, filling in any gaps and hollows with concrete.
After 48 hours, dampen the walls and skim the entire hole with a ½ inch layer of fibre reinforced cement. Next, use mortar to fix an edging of bricks and slabs, allowing for a 2 or 3-inch overhang. Paint the inside with a good quality waterproof sealant, when that is dry you can introduce water.
Finally, bear in mind that for all types of pond, filters, lights and other features will need electrical and hose connections, so remember to allow space for these while adding any edging materials.