Most of the time when I see this type of post, cracked concrete, the person wants to add some caulk. It's good to see you have the right idea with the rebar. You can do what you said, but it would be a lot of work and I think you would still get cracks down the road. Rebar really needs to be continuous throughout the structure so when cracks happen, and they always do, the rebar keeps the cracks from opening up. So what I would expect is you would stitch together the cracks with rebar and new cracks would appear other places. Impossible to predict, but that would be my expectation.

It's really a question of how much work you want to do compared to how much more useful life you'd get out of the structure. You can, for example, just patch the cracks and apply a rubberized paint to seal the concrete. You apply several coats to build up a thickness. The greater the rubber thickness the larger gaps it can handle as new cracks appear. If you were hiring me to do the job I personally wouldn't take the job because the risk of it not working is too high.

I would normally just lay a EPDM liner over the concrete and you'd be good for 25+ years. However, the shape of your pond, might make that difficult. You could go with a thinner layer like PVC just to make forming to the contours easier.

Another choice I would consider, and probably how I'd go, is to remove all the concrete and then lay a EPDM liner. I'd probably also reshape the pond just to make the liner easier to lay. It's those narrow areas that make liner difficult. Hard to tell from pictures for sure what I'd actually do. Also depends on your plans for the pond. Fish? Plants?

The tree roots aren't normally a problem with EPDM.

Thanks Waterbug, Yeah, I know it's a a difficult situation. I appreciate the advice, really. We're still weighing all our options, including, and up to, just ripping it out and starting over. It is part of the overall historic flavor of the property, so I am hesitant to junk it entirely.

I realize the potential for follow-on cracks if we patch the existing structure. I was thinking to fix the big cracks with concrete and let a sealer take care of the hairlines. Do you have a recommendation for a rubberized sealer? I saw several pond sealing products, and a couple of threads here that advocated using fiberglass gel coat sealer. I don't see a particular advantage to one or the other, other than price.

Fortunately, my wife is up for any size project, so my options are open. Definitely fish and plants, and definitely a waterfall, ultimately. I already ran water and power out to the site so really I am just deciding on the structural fix now.

Appreciate any additional input. Thanks, Mike

I read a thread recently of a guy who used RubberizeIt but I've read other threads using different products. They all seem to have worked well for them. Generally it seem to need a pretty smooth surface. ---I'm blocked from mentioning the site so I can't refer you---.

I can understand what you mean about it fitting the property. Most of the time these things are just a shallow hole with some chicken wire and some mortar. Yours has a really interesting shape and some real effort went into its construction.

Plan E could be to rebuild the structure. You could use the existing structure to build form (not too hard). Then remove the forms and the old concrete. Lay a liner, add the forms, and pour new concrete. You'd have the same pond but ready to last 100+ years. I didn't suggest it before because it's a fair amount of work and expense.

Hi
Was curious about the shape . Why the very narrow part.??
is that a concrete wall in the background?? Planting bed ,and why such an odd shape?? .Apparently it's under a lot of trees??. I'm guessing you're in California so won't have much problem with snow and ice?? but still a lot of shade.
I think if it were mine . I'd take it out and move to a better location and a more practicle shape . What will you do with the surrounding area?? Good luck with whatever you decide!! gary

From the picture, I'm sure this was a very cute pond and landscaped area, but nature has won with larger trees, more roots, more shade, so unless you'e wanting to do a restore to original landscape, moving the pond may well be a better choice in the long run; better pond results and less maintenance, if you're there for a short duation, them one of the above may work for you.

Thanks, guys. The whole property was incredibly overgrown when we bought it. It's about a third acre, an so far we have removed 56 trees. From saplings to 40 footers. (as a side note, we still have lots of trees, including an 80 foot Canary Island Date Palm, four big redwoods, and a huge Valley Oak, etc.)

The Acacias are destined for the chipper shredder, and I'll stump them out from the pond, so no future root worries there. The palms have small rootballs that are not a problem, so they get to stay. We'll add some tree ferns to recover some shade after we remove the Acacias. the palms and ferns won't much up the pond with leaves, either.

Gary, I have no idea why the narrow bit, and it's also very shallow there, just over a foot. The concrete wall in the background is the rest of the pond, roughly two feet deep. It's a weird shape, but I've kinda gotten to like it. Yeah, it's California, south of SF about 80 miles. It snowed here twice in fifteen years, for five minutes total. Doesn't freeze either, but it rains for two solid months, and then dry as a bone for about the next six or seven months. I think the rain saturated clay expansion, then drying out and contracting didn't do the pond ant favors either.

Waterbug, I had seen a recommendation from another guy that, in this situation he would put a liner in the existing structure, and then concrete again. I was giving that some thought.

Well, this weekend is cleanup, remove all the rocks and debris. I'll figure out how to add some pictures after I have it cleared.

Hi Mike,
Waterbugguy and I used to live in the bay area. I lived there for 60 years and can confirm your statement about 2" of snow except that it can be extended to the entire 60 years. I guess that you are assuming that the Acacias are just weeds. I was just going to point out that they should be much bigger if they had been there for many years. This might also suggest that the pond might not be all that old and necessarily worth saving.

"I had seen a recommendation from another guy that, in this situation he would put a liner in the existing structure, and then concrete again. I was giving that some thought."

I normally mortar rock over EPDM liner, so I like the idea too. The only thing that holds me back in this case is the pond size, especially the narrow area. Even with a thin stucco type covering over plastic or SS mesh, with the liner folds I'd guess the total thickness would be in the 2-6" range. There's just no way to get a EPDM liner fold to lay flat, so it puffs out a couple of inches. When you mortar over it you'll want a smooth finish rather than seeing the fold puffs though the mortar. So the thicknesses at the folds kind of dictates the overall thickness.

You could try a liner thinner than EPDM.

The result would not have the same as you have now.

I'm not there, so can't really tell...and I don't know if you've ever done anything like this before...but removing concrete that isn't reinforced is surprisingly easy to break up and remove. Few light whacks with a sledge. I find it very satisfying. You can get a 10 yard dumpster for about $275. Or the debris could be the base for a waterfall (easier than carrying it to the dumpster).

After much thought and discussion with DW, we are going to go with stitching the cracks, but both inside and outside the pond walls. We will also pour a new bottom to the pond, on top of the old. Then we are thinking to go with a thick layer of the Rubberizit coating. First, of course we send the Acacias to the great mulch pile in the sky. Then, we dig! This looks like the most cost effective way that we have, preserving as much of the original structure as possible, with the best chance of success, short of a complete rebuild. We want to keep the original as much as possible.

We did some major cleanup. Good news is the pond is a couple inches deeper than I thought, bad news is it was nasty! Below is the before and after. May not look like much, but below that is a pic of the seven 35 gal trash cans of leaves and muck, and the piles of rocks we removed. Still a little to go, but almost done. We will reuse a lot of the rocks for the edging on the pond, as well as a planned two-level waterfall, about which I will ask questions of you guys in the future. Thanks for all the input!

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Comment and comments are always appreciated. : )

The best way to learn is by experience.

Those leaves and muck can start a great compost pile that will do wonders for your garden plants.

As an old house nut and lover of historic concrete (my 100 + year old house is made out of it) I am pleased with your decision to keep the original pond - love the funky shape and there is something really neat about how taht thing fits between all the trees. Someone obviously spent a lot of time getting the curves right.

Not sure about fish though - is the rubber coating safe for fish? Not all rubber products are.

Hard to get a sense of scale from the pics - how deep/wide is this thing?

I'm an old house fan too and that brings up another tip. This is for fanatics like me. New concrete looks new, and will look new for many years. Spray diluted muriatic acid onto cement after it has cured 3-4 weeks. It instantly ages the cement. You can repeat to get the age you want.

There seems to be a growing trend, especially in Europe, to use rubber type coatings. The coatings are said to be safe and there are many ponds that have had fish for several years without a problem. Long term safety is unknown, but that's true for EPDM too. Firestone's original "fish safe" test was placing 6 goldfish into a pond and in 2 weeks they were alive so it was deemed "fish safe".

Hi Waterbug, yeah, upon reflection we're veering back to liner. Now that the pond is cleaned out, there's a lot more damage than I originally thought. I think your advice is well taken, and maybe I can ask for a bit more?
If you cement over a liner, how thick do you go?
If you don't use rocks in it, do you reinforce with something like fabric or chicken wire, and will it immediately crack where the folds are when the water pressure hits it?

Hey, the tip about the acid aging of concrete is great. Will try it, I have a lot of new sidewalk...

Sharon, I agree, but I has a huge compost pile already!

Another open question. On Tuesday, the tree people will be here to remove the Acacias. DW and I are looking at what we can replace them with. We already have windmill palms, and I am thinking some tree ferns too. We want to recover some shade, but not spend the rest of our lives cleaning out leaves or fruit. And, of course, not something that will pick up where the Acacias left off on the concrete destruction or poison the fish... What have you all seen or have that works well?

Hi kashka_kat, thanks, I agree, it's a really funky shape. I think it'll be cool when done. We're looking at putting the waterfall alongside the thin section, and possibly turning that into a sort of fish tunnel with some overhanging rocks. I am no expert on the liners, but many people seem to have used the rubber coating with success. I think we're going back to the liner, so I may never know...

I love the shape. Very unique. Someone with more experience than I have may comment about having "dead" areas where there isn't as much water circulation as there should be. When mine was being contemplated I wanted to avoid the "octopus" factor because of this. I hope that you can incorporate a stream with a couple falls rather than just a falls because it would really enhance the casual informal wandering look. You are going to have something very special when this is finished. How deep is it?

One way to keep the circulation good would be to have a falls that divided into two streams - one in each of the basins.

Please post the progress as you proceed. I'd love to see this pond when it is finished.

Putting a stucco type layer over liner is a tricky deal, but not really very difficult. I normally mortar rock over the liner which is easier, cheaper, different look.

For a stucco layer...there is no standard building practice for this, it's more art. Two basic ways, mesh or no mesh.

For mesh you need something that won't rust. Stainless steel mesh is best but plastic is OK. There's no such thing as plastic mesh for concrete so you have to use fence, or netting. For the SS you have to be very careful with sharp edges, turn them all up. With mesh is once the mortar is on the mesh if you vibrate the mesh very much the previous stuck mortar slides off. So as you put on the mortar the stuff you already added slides off. Very frustrating. The trick is to light flick some mortar onto the mesh. Cover as much as you can, but back off if previous mortar falls off. Your goal is to get some mortar behind the mesh in places so the mesh lifts up off the liner a bit, about 1/4", but a little less is OK. Let that cure for a day. Now the mesh will be much more rigid. You should now be able to skim a layer of mortar on with a trowel. Nothing fancy, a thin coat. Let that cure for a day. Now you have a nice firm base. Now you can apply your finish coat. Easier to do the walls first and come back on do the floor.

The no mesh way is easier but you use a lot more stucco. Pour the floor first. Say about 1" thick. It will crack but because it's the floor it really shouldn't go too far. By pour I don't mean pour like water. Mix the stucco so like mashed potatoes. Put it in the pond and tamp it down until about 1" thick. Because the stucco is thick you can get this initial "pour" to go up the sides a bit, do that. Let this cure a couple of weeks if you need to stand inside the pond to do the walls. If you can hang over the walls you only need to wait a day for curing, or really even just a few hours.

The floor now acts to hold up the stucco you're about to add. You go around the pond adding stucco maybe a 6" course at a time, or whatever works for you. Let each course cure for at least a few hours so it can support the next course. When done you can now add a final finish coat.

I would say 3/4" thickness with no mesh would be the minimum. There's a fiberglass reinforcement for stucco you can use in the base coat. It can stick out of the stucco so not good for the final coat.

I've said stucco but you can use mortar, same basic thing these days.

You can use a synthetic stucco for the final coat but to me not worth the cost.

You can add color to the final coat if you like.

If you age the final coat just do what's above the water line. Just no point doing below the water line and the acid removes cement that you want. There are lots of people who say cement in a pond should be acid washed to keep the pH down in the pond later. Bad myth. It does nothing but expose new fresh cement. Cement carbonizes, kind of like rust, which seals the underlying cement from reacting with the water. This is why cured cement doesn't dissolve in water.

The voids behind the stucco caused by folds will fill with water, the stucco structure is far from water tight. That equalizes pressure so the result is no pressure on the stucco.

Fantastically detailed response, Sir! Thank you very much. We have next week 'off' (a shutdown, furlough, whatever...) so we'll be working on it. : )