Repairing leak in 34 Y/O pond, help please!

[AdoraBelle Dearheart]

Pond is roughly 12 by 18 FT, 1-3 ft deep, varying levels of depth, built by my dad (I helped dig it out as a kid!) 34 years ago. Contains an estimated 40-50 goldfish/shubunkins that have bred in there for years, well used by frogs/toads/newts.

Dad built the covering frame a long time ago after a visit from a heron almost cleared the pond out. I'm planning repairs for the frame, surrounding fencing that's really only there to keep the dogs safe.

The pond has been leaking water for a couple of years, there's a certain level it won't rise above anymore, although it used to. It's topped up/water changed often in summer, but now within a day it's back to this level again. I believe this crack between two rocks (see three pics below) is the main source of the leak, and a friend who works in the field also thinks it's the right spot, due the plant growth and dampness around the area of the leak, and by topping it up and following where the water seems to be going.

He has given a quote of around £3,000 to deep clean, new filtration, repair the pond and fencing etc. He's been very generous with free advice, but I don't want to take advantage of his knowledge, but also could never afford that! I know what dad would have done, he'd have repaired it himself. I want to do the same.

While I'm about it, I'm sure the rockwork all around that level could do with re-pointing in places. I've never worked with concrete before, but I'm not bad at general home repair and decorating, so I'm comfortable giving it a go! Having never used concrete before though, I got a tub of ready to mix concrete, only need to add water and mix the amount I need. It arrived this week, but of course, with British weather, it's now rained all week since it arrived, even though it was beautifully sunny and dry before...

Just some more pics of the pond, lots of live plants growing in and around it that I hope to preserve. I do have to thin out the plants several times in spring/summer or the pond gets choked out with it and leaves no swimming room for the fish. Hornwort and elodea, duckweed, rushes, watercress etc. I have to be careful especially in newt breeding season - while clearing some watercress this year, I found more baby newts than I've ever seen before! So it's a slow, methodical process to make sure I don't remove any babies of any species.

I'm going to need to drop the water level slightly to repair the crack properly, which I guess I'll have to set up a syphon, or do it by hand with buckets - but with a 12 by 18 ft pond, I'm dreading it a little! The concrete mix also apparently sets FAST, so I have to have the brickwork prepped, clean and ready before mixing it.

I guess I'm just intimidated about this and looking for any advice! I know the concrete is safe once dried, but what if I drop any wet bits into the water while trying to fix this gap?

 

[Wills]

Could you use pond foam instead? There are a couple of brands like Oase and Superfish that do it. Its a fish safe black expandable foam that you could squirt in and let it expand and then trim down.

Wills

 

[AdoraBelle Dearheart]

Could you use pond foam instead? There are a couple of brands like Oase and Superfish that do it. Its a fish safe black expandable foam that you could squirt in and let it expand and then trim down.

Wills

Isn't concrete safe? That's what was already used. A black foam would stand out and I think look a bit ugly against the otherwise grey stone and mortar in the rest of the pond?

 

[Wills]

Isn't concrete safe? That's what was already used. A black foam would stand out and I think look a bit ugly against the otherwise grey stone and mortar in the rest of the pond?

I think it is but some concrete can effect water I think? The foam just seems less scary from a DIY approach haha

 

[AdoraBelle Dearheart]

I think it is but some concrete can effect water I think? The foam just seems less scary from a DIY approach haha

From what I've read, concrete is waterproof once cured, it's just getting it in the gap without any touching the water that makes me nervous! I guess I need to drop the water level low enough that I can isolate the gap and put some protective layer under it, like a plastic liner/net beneath the bit I'm working on.

I'm wary of dropping the water level too low though, there are a lot of fish in there. I could remove some to a large container, but I'd prefer not to put them through that, or risk stirring up too much sediment trying to catch them. Pond has been unfiltered for decades now, and we're only just beginning to sort that after adding a smallish pond filter. Looking for a larger pond filter second hand at the moment.

 

[Colin_T]

Concrete should be fine if a little bit drops in the pond.

The brick work doesn't have to be dry and concrete sets harder and stronger if the brick and cement is wet or damp for the first 12-24 hours. It's one of the reasons they pour concrete first thing in the morning, so it's cooler and the cement has time to cure while it's damp. Concrete that dries too fast will be more likely to break or crack. Quikset concrete is designed to dry quickly but still cure.

Ideally you do concrete work when the temperature is below 20C (shouldn't be a problem in the UK).

Just clean the old concrete off the rocks and use a wire brush to remove any loose bits on the rock/s. Make the cement up and use a trowel or spoon/ butter knife or hand to apply it to the rocks. Have a reasonable amount (1/2 inch or however much is currently there) of cement and fill any gaps after the rock has been put in place. Clean the excess off while it's dam. Keep it shaded and leave it for a day or two. Then fill the pond up.

Only make enough cement to do the job. Unused wet cement can be poured into a small hole dug in the ground and left to dry. Then lift it out and dispose of it.

Wear rubber gloves when handling the cement. If you want to keep the bucket and trowel after doing the work, rinse it outside under tap water. Do it in a hole in the ground so the cement doesn't end up all over the lawn. If you don't want to keep the bucket and trowel, just let them dry then throw them out.

Wear a dust mask and stand upwind when pouring the dry cement into the container, and when mixing it. The dry cement mix is very fine and blows everywhere so a dust mask and staying upwind is helpful to avoid getting covered in the stuff.

It's pretty easy to do, a bit like making a mud pie and sticking bricks together.

 

[Naughts]

Is there a liner or plastic mould that leaks, or is it just through the rocks?
Would it be prudent to take a series of photos of the rocks before you take them apart, to assist when placing them back together?

We would always leave removed plants and algae on the edge of the pond so creatures could easily find their own way back in.

 

[AdoraBelle Dearheart]

Concrete should be fine if a little bit drops in the pond.

The brick work doesn't have to be dry and concrete sets harder and stronger if the brick and cement is wet or damp for the first 12-24 hours. It's one of the reasons they pour concrete first thing in the morning, so it's cooler and the cement has time to cure while it's damp. Concrete that dries too fast will be more likely to break or crack. Quikset concrete is designed to dry quickly but still cure.

All of this is so helpful, thank you!

Ideally you do concrete work when the temperature is below 20C (shouldn't be a problem in the UK).

Haha, absolutely not a problem! It's just been the non-stop rain that's put me off at the moment. But I didn't know about doing it in cooler temps etc, so that's very useful, thank you!

Just clean the old concrete off the rocks and use a wire brush to remove any loose bits on the rock/s. Make the cement up and use a trowel or spoon/ butter knife or hand to apply it to the rocks. Have a reasonable amount (1/2 inch or however much is currently there) of cement and fill any gaps after the rock has been put in place. Clean the excess off while it's dam. Keep it shaded and leave it for a day or two. Then fill the pond up.

Dad used to mix cement himself with concrete powder/sand/water, remember watching him do it several times, but I wasn't confident about getting the mix right myself so it would be the right consistency for working over the pond, so I chickened out and ordered the ready made stuff. But we still have his trowel and wire brush, bucket etc used for cement work.

Is there a liner or plastic mould that leaks, or is it just through the rocks?

Nice to see you, @Naughts !
I think I remember him using a plastic liner in the lower level of the pond, cementing it into the edge of the pond then building rockwork higher above that level. I don't think it's leaking that far down, so many years of sediment would block any splits down there I think! But mainly because the place the water level stops is always at the same level, and that's above that pond liner level.

The bit where he cemented the liner in, he deliberately left a little ledge sticking out, so frogs, toads etc could easily get out of the pond. Same with leaving small gaps between the pond and the frame, so they can get in and out, but herons can't get at the fish.

Would it be prudent to take a series of photos of the rocks before you take them apart, to assist when placing them back together?

That's definitely a smart idea! I'm hoping I won't have to remove too many, mainly the two around the main leak. But I guess I'll know more once I start cleaning and prepping and see how the old mortar is... taking some pre-work photos is a smart idea, thank you!

We would always leave removed plants and algae on the edge of the pond so creatures could easily find their own way back in.

Yes, for sure! I think the baby newts especially liked the watercress, so they could be out of water while safely wet and able to get into the water, I guess! But the watercress forms these dense mats on the surface, and the hornwort etc forming thick masses underneath and getting entangled with the watercress roots too.... it was getting to be way too much. I had to remove a load, but very carefully a few strands at a time, checking carefully and putting baby newts back! I left way more weed in the pond than I really wanted, to give the newts more time to finishing developing and leave the pond. They're so cute, and I'm glad the pond has been home to newts for so long.