Concrete Pool Repair

I have two concrete garden ponds, each containing about 500 gallons. They were constructed using reinforced free form concrete laid up by hand and are about 20 years old.

They are connected by a foot long, foot wide and foot deep channel. Because of the way the ground moves and the inflexibility of concrete, I realize they should not have been constructed in this way, but that’s just the way it happened in a momentary lack of thinking.

Every several years a crack will re-form in the connecting channel and the ponds will drain down to that level. The crack is narrow, only about a sixteenth of an inch, but that’s plenty.

To repair the crack, I’ve tried various materials, including silicone, but none holds as well or as long as Shoe Goo. It adheres well to concrete and is flexible. Unfortunately it becomes hard after a few years and no longer flexes. To perform the repair, I chisel the crack so it is about ¼ inch wide and deep, and clean it out with lacquer thinner. Hopefully the next time the crack appears the weather will be good.

I would like to consider a different material. I know there have been many improvements in materials over the years. One approach would be to use a flexible epoxy patch in the chiseled out groove. The Marinetex Flex Set is one which comes to mind, although I have no experience with it. The other approach would be to apply a flexible paint in the area. The flexible paints come in 1 gallon containers which cost around $100, which is pretty expensive considering that the entire pond would not have to be covered.

Because of the shape of the ponds and an overhanging lip in one, I don’t think a rubber liner is reasonable.

I would appreciate your ideas and experience you have had with similar situations.