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Concrete Lined Pond Repairs. How to repair a leaking concrete pond.


Concrete ponds are notorious for springing leaks. The main reason is either ageing, or poor construction - materials, methods etc - in the initial stages. Concrete Ponds in clay soils are particularly at risk, because of the inherent nature of clay soil.

Clay soils shrink when dry, and expand when wet. This constant shrinking and heaving of the soil surrounding the pool cause the pond either to break its back, or sometimes just disturb a week point, leading to the inevitable leak.

Spotting where the leak is on a concrete lined pond is normally quite simple. As with a plastic liner, the water will eventually subside to the level of where the leak is. (Sometimes, if there is a high water table in the surrounding soil, then the water will only subside to that level and maybe not down to the actual pond leak. This is rare these days with reduced water table level.)

Once the water has settled in at the level of the leak, then take out a few more inches of water - especially on a hot drying day. The leak - normally a crack - can usually be seen by the wet tell tale marks on an otherwise dry concrete surface. Once the leak has been isolated, then proceed as follows.

Firstly, it will probably be necessary for you to drain the entire pond, for there will be quite a bit of debris falling into the pond, together with wet cement. neither of these will be good for fish!

  •  Use a hammer and cold chisel - masonry chisel - to remove any flaked or loose material from around the leak. Then - once the extent of the leak is seen, chisel away all loose concrete in the area, and then also a few inches into the solid remaining pond surface. It is no use simply clearing away the loose concrete from the crack.
  • Clean the entire area with a steel wire brush, and then a hard bristle brush - preferably exposing some of the aggregates that were used in the original concrete.
  • Fill the crack - if it is small enough - with waterproof mastic cement, or one of the new waterproofing agents based upon silicone, with a high adhesive property. If it is a large crack or leak area, then you will probably have to re-build the area with a waterproof cement mix in stages. This is best done by someone who has good building or plastering skills rather than by the DIY expert (!)
  • Finally after a day or so of drying, then give the area a couple of coats of special pond waterproofing paint. Leave this to dry according to the maker's instructions, then you can safely re-fill the pond and re-stock.


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