Pond against existing concrete patio

[Karl_S]

Hello All,

I am looking to build a pond and ideally would put it against an existing concrete patio. Is there a way I can get the water right to the edge of this concrete? Meaning no stone or blocks added to the edge of the concrete? I MIGHT be able to put tile down over top the concrete, but that may not go over well with my wife. I would have to find something porous enough to not be slippery when wet.

My idea is to have a waterfall where the hosta and pagoda are in the photos. have a stream come down a bit and open to a pond at the bottom area of the first photo. A stone "bridge" crossing the stream a step or two from the stairs. My thought was to dig down and put a block wall along the existing concrete, below grade, to allow for a bit of depth and to support that side of the bridge, and use a flexible liner for the pond. The question is how would I get any liner along the concrete with something that looks nice. Maybe some brown composite/poly lumber with anchor bolts into the concrete? I am hoping someone here has some experience with how to handle this. What would be the preferred option for achieving a clean look here?

 

[Tula]

Others with more experience will chime in. If it were me, I'd raise the pond's edge....giving you someplace to sit and view / feed the fish, also planters would look nice on it.

 

[j.w]

@Karl_S

 

[addy1]

Welcome to our forum!

 

[combatwombat]

Sounds like a cool detail. Will look great.

I think what I would do in this case would be to dig a shelf just deep enough to support some base material + 1 CMU block, recessed beneath the existing patio. Then liner over that and some sort of continuous wedge to fill the gap between all of that and the bottom of the concrete. Maybe a tightly packed mortar.

Legend:
White: Existing concrete/earth
Yellow: gravel base
Grey: CMU block
Red: Liner

 

[combatwombat]

Add’l thoughts:

1: CMU edges are sharp. I would grind them to a rounded bevel using an angle grinder with a concrete cup blade.

2: Put a nice thick piece of underlayment between your block and your liner.

 

[Mmathis]

Hello and welcome!

That is a lovely spot!

 

[Karl_S]

The problem with that design is that the underside of the patio may not be so flat. I suspect there is a couple inches of rock under the concrete and the bottom surface is jagged. That said, I could use a concrete saw.

After creating this post I did see the one about building against existing boulders. I saw a large write-up in that which talked about the composite garden liner. It talked about spacing things off the boulders, though, and was a bit confusing without pictures/drawings. Since this is smooth, though, I may be able to use flexible garden edging to press the liner against the concrete.

Please excuse the rough sketch.

 

[combatwombat]

@Karl_S: I think your design would work fine as long as you don't mind that exposed edge of the liner along the patio edge.

I assume your concern about the jaggedness of the underside of the patio concrete is just the aesthetic of the edge? There are all kinds of thick mortar/cement mixes you could probably use to tool and clean up the edge if you wanted. Maybe a concrete saw to chamfer the edge to give it a finished appearance. That would probably be quite difficult (and dangerous) to freehand.

 

[addy1]

That little circle area, it appears you drew in a small shelf. On that small shelf you could stack rocks to cover the exposed liner edge.

 

[Karl_S]

@Karl_S: I think your design would work fine as long as you don't mind that exposed edge of the liner along the patio edge.

I assume your concern about the jaggedness of the underside of the patio concrete is just the aesthetic of the edge? There are all kinds of thick mortar/cement mixes you could probably use to tool and clean up the edge if you wanted. Maybe a concrete saw to chamfer the edge to give it a finished appearance. That would probably be quite difficult (and dangerous) to freehand.

I could "freehand" a chamfer OR a flat cut pretty close with a circular saw, but would probably use a guide. Maybe I do this and then I can attach the liner to the underside of the concrete suing the same method I drew up for on the side. Then block up to it as well. Honestly, though, if I have enough anchor bolts, and thick enough liner, I may be able to get a decent seal and let the water go above the liner there. And Silicone. LOTS of aquarium grade silicone!!! Replaced yearly.

I was thinking the water level would be up against the concrete. But maybe just below is fine. The ground is fairly level perpendicular to the concrete, with a very slight slope towards the camera in the pictures.

 

[Karl_S]

That little circle area, it appears you drew in a small shelf. On that small shelf you could stack rocks to cover the exposed liner edge.

The circle area was just to show where the enlargement above was coming from. Old drafter in me. Was going to do lines up and a circle around the detail but ran out of index card. There will be a small shelf at one area for holding a bridge stone but the CMU block may be even with the edge of the concrete everyplace else. If not, I could do a stone or brick and mortar edge around the concrete, but then I have to do it up the side going away from the pond as well as well. Basically my wife expects things to be consistent, so if I do something between the pond/stream and the concrete, outside of water, I need to do that around all the concrete.

 

[combatwombat]

if I have enough anchor bolts, and thick enough liner, I may be able to get a decent seal and let the water go above the liner there. And Silicone. LOTS of aquarium grade silicone!!! Replaced yearly.

Do you have any kind of freeze/thaw cycle in your climate? If so, expecting a silicone seal to hold water between liner/concrete is probably an exercise in futility. I guess if you replace it every year...

 

[Karl_S]

It is Maryland, USA. Top of the Chesapeake. Definite freeze/thaw/excess humidity climate. Hence the " Replaced yearly." Possibly more often than that. Frankly, if I can get a good gasket style seal, though. I MAY be good. Or I just have the water level stop just below the concrete and tuck the liner under the concrete. Probably this later idea is best.

 

[addy1]

Basically my wife expects things to be consistent,

I am lucky hubby just says do what you want!