One of the main reasons for a above ground pond is the closeness of it's feel. You can sit on the edges and interact more closely with the surroundings. A lot easier than sitting down on the ground next to a liner in-ground pond.
The main disadvantage of a raised pond is that it is exposed to the elements and mainly the cold. Care must be taken so that damage does not affect the structure or it's inhabitants.
A raised pool can be fairly simple to construct using hollow concrete blocks that can be found anywhere. If you want some fancy shapes, you will have to pour concrete and use forms.
The inner faces of the walls have to be rendered with concrete mixed with water proofing. Complete waterproofing can be achieved by using plastic sheeting in the floor and between the inner and outer skins of the walls.
Alternatively, you could opt to use fancy bricks or other materials to conform the structure to blend to the surrounding buildings. Cost, however may prohibit this way of thinking when compared to the costs of block construction.
Installation Of Above Ground
When digging the hole for your pond, be sure you dig it at least 6" larger than the finished size. This will allow for the thickness of the actual concrete structure itself. You should use the same excavation methods as you use with a flexible liner pond. If any part of the pond will have slopping of more than 45 degrees, you will have to use forms in its construction.
Lining It:
Concrete can and is routinely laid right on the ground, in most instances. We recommend that you use a liner prior to pouring the concrete to provide a vapor barrier and prevent the concrete from drying to rapidly. Be sure to remove all rocks and roots before you lay the liner. Poking holes in it renders it useless as a moisture barrier.
The Concrete:
Start by working outwards from the center and spread a 4" layer of concrete over the entire excavation. You can use a plaster trowel to even it out and make it relatively smooth. Make sure that the plant shelves and floor are fairly level. Next press a layer of chicken wire into the wet concrete to reinforce it. On top of this, spread another 2" of concrete. This is going to be your final layer, so be sure it's level where needed. You should use dampened sacking or other material to lay over the new wet concrete so that the material cures slowly. You may also water the surface with a fine mist several times a day until it has completely set.
Water Sealer:
Once the concrete has set, you can waterproof it to prevent lime from escaping into the water. This lime is harmful to both plants and fish and leaves the water a milky color. Use a sealant in a crystalline form and mix it with water to apply. If you would like to change the color, you can also paint the surface with a waterproof plastic paint found in paint and hardware stores.
Raised Ponds:
We do not recommend constructing a raised pond unless a portion of the construction is underground. Water is a heavy liquid and places a lot of strain on the concrete. We recommend a 4' deep pond with 2' under the surface of the soil and 2' out. This gives the appearance of a raised pond with the stability of an in ground.
Be aware that the upper section should be constructed using wooden forms with steel bars that start at the ground level and end up a few inches below the top of the upper forms.
Final Note:
If any of this type construction is the least bit intimidating, we recommend that you consult a local mason. Drive around a construction site and talk with the workers. Many of them work on the side after work and on weekends and can save you big bucks in the process.
