How best to renew a leaky cement-lined pond?

August 14, 2022 2:04 AM

We have a cement-lined pond that hasn’t held water for a long, long time. We’ve removed the dry plants and earth from it and would like to make it watertight. What would be the easiest and/or best way to do that?

It’s about 10ft/3m in diameter and about 20in/50cm deep in the center. Here’s a photo.

There’s one obvious crack in the cement that could be filled but maybe we should do more than that to be sure? What would you do?

We’re in the UK in case that makes a difference to materials, etc.

posted by fabius to Home & Garden (9 answers total)

Pond liner. You might like the overlap to create some water-reed edging.
posted by Thella at 2:26 AM on August 14, 2022 [4 favorites]

One fundamental question is whether you go with the option of putting something on top of the existing liner or whether you get rid of the existing liner and dig down first. The former option will be easier but will make the pond shallower. My thought is that 50cm depth is not really enough to good temperature buffering for hot or cold conditions - better to have a part of the pond go down to 70 or even 80cm. A solution which sits on top of the existing liner will make the pond even shallower. Joel has some good videos on nature pond construction - like this- which you might find helpful.
posted by rongorongo at 2:34 AM on August 14, 2022 [1 favorite]

That's a crappy pond. I'd get it dug out - hire a breaker for a day (they're great fun) and take out the cement/concrete. From the image I doubt it's very thick, which may well be the reason it's cracked. A 50cm deep pond that gets rapidly shallower towards the sides is not suitable for fish, etc. If you start again you'll get the chance to have the pond you want (the right depth, shape and size).
posted by pipeski at 3:38 AM on August 14, 2022 [1 favorite]

Response by poster: (We have another bigger, deeper, pond that has goldfish in so we're not super bothered about this one being the best pond ever, but it would be nice if it was more of a pond than a damp cement puddle.)
posted by fabius at 3:40 AM on August 14, 2022

I would be tempted to build up the sides, add soil, and have a raised garden. It would hold some moisture, a good thing in many places.
posted by theora55 at 8:36 AM on August 14, 2022 [1 favorite]

You live in an area which usually has an abundance of water. I'd try just adding a layer of parging mix over the whole thing and see if it holds water well enough. If it worked well enough before cracking again, use silicone cement filler for the cracks, or using an elastomeric paint over the whole surface, but they probably costs more than a liner.

Plus I'd want a smoother surface before putting pond liner over it.
posted by flimflam at 12:29 PM on August 14, 2022

A pond liner is probably the easiest fix and it will hold water fine but, as others have mentioned, the pond would be much better if it were deeper. The pond liner material linked by Thella above shouldn't need a cement base anyway, so you could dig the existing one out and make the pond deeper and whatever shape you want then just lay the liner in and put rocks or whatever you want around the edge. I've built a few ponds in this way and had no problems. I've built a couple with concrete and had issues with cracking and leaking - the concrete would need to be at least a couple of inches thick and reinforced to resist normal ground movement.
posted by dg at 2:44 PM on August 14, 2022

I doubt it applies to your situation but David Pagan Butler’s Organic Pools (UK based) are just so cool! Don’t miss his YouTube videos.
posted by kiblinger at 8:03 PM on August 14, 2022

Response by poster: In the end we used a couple of packs of Pond Putty which, so far, seems to have done the job. I think it's repackaged Milliput, used for model making and plumbing.
posted by fabius at 12:43 AM on January 10, 2023