Sealing my concrete pond

Hi all,

Some of you may remember my posting earlier in the year, saying I was planning a pond in the shape of a yin-yang symbol. It also needed to be robust enough to take doggy claws, and I was planning on facing it with drystone-wall-type stone. Advice from Watergarden and others back then was to go for a concrete pond.

The concrete part of it is now done, and I've applied a cement skim (with added Wizard Fibre). Once I've got a waterproof pond with cement sides, I'll then apply the stone facing - I think that's a better plan than trying to waterproof a stone facing, where bits of stone can (and will) naturally come loose from the cement around them. Anyway, a pic of progress to date.

So far, so good. However I've run into a problem with the local water table. The bottom of the pond at the lowest part is slightly lower than the water table, with the result that water seeps in. That's stopped the cement in that part of the pond from setting and sealing properly, so it's a bit porous and water's still seeping in after the cement skim. And of course, when I fill the pond, wherever it's seeping in now, it'll seep out later when the pond's full. :-(

I've got a couple of pots of P1 pond sealant which I'll be using to seal the cement. But the P1 instructions say that surfaces need to be dry or slightly damp, but not actually wet, so that's probably no good just yet. My plan is to get some P3 and try using that to seal that corner, and hopefully (according to their advertising blurb) that'll seal it well enough to apply P1 over the top as the final waterproofing. Does that sound like a plan? Or do other people have other suggestions?

If I'd known this'd be such a problem, I would have put down some poly sheeting before I concreted, to keep the water out. But it's too late for that now.

Cheers,

Graham.

 

I have no idea if it will work, to be honest, I doubt it. (Since the water will try and lift anything)
I would however, suggest that you excavate another hole, deeper than you have, put a liner in it, a couple of old buckets should work and put a sump pump (with float switch) in it with a pipe to waste and leave the sump pump switched on.
Obviously the buckets need to have lots of small holes, but the idea is to prevent soil being pumped out.

OR you could leave it till summer next year.

But did the hole not start filling when you were digging?

 

Not significantly. I hit damp clay and stopped there, precisely because I didn't want problems holding back the water table. A little water seeped back in, but it stopped below the level the concrete is now - there was only about 1cm of water in the bottom at the deepest point of the hole. Maybe the rain has raised the water table enough to knacker things.

I guess I'll get myself a bit of P3 and see how it goes. It's not that expensive, so it's worth a go. Digging another hole to drain the water table locally is a good idea, but it'd be a major job, so I'd rather keep that in reserve if all else fails. It's a good plan though if I can't get it sorted by any other means - thanks for that.

The worst part of the whole thing for me was trying to explain to my wife why this porous bit would be a problem. The one time she's said I really explained something well to her, it was when I was about 4 pints down and had to concentrate to talk and think clearly, which gives you an idea of her technical abilities. So I quote our conversation, verbatim:

Me: "If the pond's porous in that corner, all the water's going to leak out."
Her: "But the water's coming in. Why's that a problem?"
Me: "The water's only coming in now because the pond's empty. When the pond's full, the water's going to leak out of the pond into the water table."
Her: "But if the water's coming in now, why's it going to leak out when the pond's full?"
Me: "Um."
(Put a full glass of water in a half-full washing-up bowl.)
Me: "OK, now the water level in the glass is higher than the water level in the washing-up bowl. If I put a hole in the bottom of the glass, the water's going to flow out of the glass through the hole, right? It's not going to flow from the bowl into the glass, is it?"
Her: "I don't know. Is it?"
Me: BOGGLE!!!!

 

Should have used a plastic cup

 

*grin*

Well, I got some of the P3 stuff, and there's a kind of good-news-bad-news thing there. The bad news is that it didn't seal the seepage. The good news is that it didn't seal the seepage because I'd put it on the wrong place, and I now know where the water's coming from.

I couldn't see it before, but with the P3 in there and releasing a slight "bloom" onto the wet surface, I noticed a couple of lines of clear water running across the bloom". Now I knew what to look for and where to look, I found a couple of tiny holes about 2mm wide at the foot of the wall which were letting this water in. I thought I'd been pretty rigorous about getting a good cement seal between the floor and walls, but it looks like it wasn't quite perfect. Shame I had to waste the P3 to find out, but I wouldn't have seen it otherwise - it just wasn't visible against the regular cement.

So now I know the cement of the pond is actually watertight, because it's happily collecting the water that's seeping in, and the water's been coming in somewhere else. That's a huge weight off my mind. The mission now is just to mix up some more cement (I'll probably use a cement-heavy mix to make sure it takes well) and fill up a solid fillet around the foot of the walls all the way round, just in case there's any more little holes waiting to catch me out. And then all being well, that should be that sorted.

 

good luck

 

Your best bet is to add a waterproofer into your concrete mix. A little expensive but well worth it.

 

Would you not agree that its a bit late for that, since most of it is built, and he has a high water table.