I built a small pond last year but forgot to add waterproofing to the cement. No harm done, or so I thought, G4 Pond sealant to the rescue. Having painted it around the whole pond (two coats) I filled it up and the water leaked out within about 10 minutes. The bottom inch or so of water doesn't soak away, that suggests to me that there's a hole somewhere roughly where the water level is. Having already mopped up the water and stuck another coat over the top that made no difference I thought that I could fill it with water and add a blob of colour that would show me where it's leaking out. I have, however, no idea what I could use that won't just mix in with the water. Does anyone have any ideas? Best I could come up with was food colouring (but that will mix) or oil (but that floats so probably won't work).
I assume from what you say that the pond is above ground? or otherwise how will you find the leak?
Is G4 pond sealant a bitumen type coating ie thick?
Could it be that you have a thin bit of concrete at that point and the concrete is porous?
If it emptied in 10 mins then it is a fairly serious leak. If all else fails and I would trawl the net for solutions/suggestions first, you can always use a pond liner.
Thanks Hogweed. I was hoping to watch the coloured blob disappear from somewhere inside the pond. It is above ground but it's surrounded by rocks, so seeing it come out the other side, so to speak, will be practically impossible.
G4 pond sealant is a plastic-based layer that sits on top of the concrete, dries [almost] clear and should perform the same job as a pond liner. I'll keep looking, thanks.
'The reason is that while the G4 Pond Sealer is able to seal hairline cracks G4 Pond Sealer is not capable of bridging larger joints, cracks or holes.'
How big is your pond?
Would you be able to fill it, watch it disappear, then mark a line where the water level drops to, leave it for a day to check the level, and then do it all over again - just to make sure it empties to the same level every time.
If it does drop to the same level every time then it is definitely a crack or hole at that level and if careful inspection cannot find it the only recourse would be to find a compound that would seal larger cracks, or put on another course of render or use a liner.
You haven't got a pump going and a waterfall by any chance??
If it doesn't drain to the same level every time, the mystery deepens, but the solutions remain the same.
You are after pond tracing dye. I did try it though and still couldnt see where the leak was, so thats not a recommendation!
maybe use a liner over the concrete?
Thanks for your replies. It's only a tiny pond around half a metre in diameter (and when it's sorted out about the same depth), though there is scope to enlarge it if I can get hold of some more [free/cheap] rocks. The plan is to have a second pond below it that it can 'overflow' into, so this top bit is designed to be more like a bird bath and the bit below better able to support something living in it (maybe some spawn). There's no pump, but I see your thinking, hogweed.
It does drain to the same level, I think that quote in relation to G4 not bridging big gaps is probably the key point. I can't see any big gaps but maybe given that it's such a small pond the quickest way would be to chip away some of the concrete at the level it drains to and just redo it. Rather time consuming but then I can only blame myself for not having done it properly in the first place!
I would just empty it and use a flexible pond liner.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
As it's a rock pond I didn't really fancy having any liner visible or covering up the rocks. Perhaps if I'd have planned for that I could have hidden the liner better. It's a little late now, maybe I'll do the bottom pond, that I mentioned earlier, like that.
I would just re-render the entire pond as its not that big.