Leaking pond - help!
Looking for some advice here. 2 years ago we had a 3.5 foot stone retaining wall built at the base of a hill behind the house. We also had the mason build a 2-foot high half-circle basin right in the middle of the wall for a pond. It looks great - only problem is that it leaks! First, we coated the inside of the basin with concrete and smoothed it out. Naturally that leaked - no surprise, since concrete is porous. Despite the fact that the walls are about 10-12 inches thick, with granite stones, mortar and cement, it leaked like crazy. So I bought a gallon of liquid EPDM. That improved things, but not by much. I don't know why, but it still leaked.
So this year I thought I'd fix it for sure. I bought a solid EPDM liner, cut it into pieces (so as to avoid buckles) and glued it back together again in place with contact cement. I then coated the entire thing (especially the seams) with more liquid EPDM. Let it dry for a few days, filled it up with water last night and........ this morning it's empty again! :-(
What seems to have happened is that the liquid EPDM did not bond to the solid EPDM liner. You'd think they would bond, since they are the same material, but they didn't. So the thin film of liquid EPDM (now dried) is detatched from the liner. There is probably a hole somewhere in the liquid EPDM, which then transfers water to the liner, which transfers it out a seam, and then down through the original coat of liquid EPDM, then through the concrete! Aaaargh!
What am I doing wrong, folks? How would you waterproof a concrete basin? This liquid EPDM is expensive, so I don't want to spend any more money on that unless it's the only option. How about tar, or some kind of inexpensive roofing product that I can buy from a hardware store? I know this would probably be toxic to fish, but I'd be happy at this point to wait a few months while it off-gasses before adding fish. Is there any other kind of "goo" that I can schmutz on there that would work better?
(I'd be happy to just use a rubber liner, but that's not an option. First, there would be too many creases and buckles, and second, there is a pipe at the bottom of the basin which runs up to a decorative spigot at the top of the stone wall. If I can ever get the pond waterproofed, I will attach a pump to the pipe for running water. Point being, the pipe sticks out from the wall, so I'd have to cut a hole in the liner to accomodate the pipe. Naturally, that hole would leak like crazy, unless I find some kind of reliable goop to waterproof it with. If said goop is so reliable, I'd rather just coat the whole pond with it.)