What underlayment to use over old concrete?

[JamieB]

In that case, fill in cracks and gaps with play sand, you could even use sand to change the slope to an easier one. Can you post pics of it? That’d give us an idea of what it’ll need more than just words can. For such a shallow depth, it must have a flat bottom. To prevent it from freezing solid in the winter, you might think of ways to deepen it, either by cutting out the bottom or berming up the sides, otherwise you’ll loose fish and plants when it freezes solid in winter.

 

[zinjy]

Here are some pics. I am still in the process of cleaning it out (it was full of accumulated dirt and weeds) and it just rained so it's not that easy to see the irregularities or tell how deep it is from the pictures, but the shallowest point is where the concrete blocks are at the end (the stacked ones are fixed in place, a center one was removed at some point and will need to be reinstalled). This is also the low end of the pool where it will overflow. Even at this depth I don't think it will freeze all the way down, based on other bodies of water around here in the coldest years, but I'd still like it be able to fill up more.

The sides are actually higher/deeper so I think I could make the pond deeper if I could increase the height of that lower end (not sure how as the concrete on either side of the concrete blocks is very irregular). If I were to line it as is, I think a considerable part of the liner (maybe as much as a foot) would be exposed at the upper end of the pool on the slope, which may cause UV damage (I'm not sure the slope is gradual enough to effectively cover with rocks, either, though I will probably put some at the bottom there anyway above where that flowerpot is, to make it easier to get out if something slips in.

From upper end looking down:

From lower end looking up

One of the irregular cracked/patched areas

Example of rough edge of pond:

 

[JamieB]

Along the edge, you could either smooth with fresh concrete, or play sand. It looks deeper than the 1 1/2ft you say. But then I consider the height of two cement bricks, and see how you reach that height, so yeah.

 

[zinjy]

Yes, I think it could potentially be deeper, there is just the issue of making the end with the concrete bricks higher, which may prove challenging (especially as the edge is lower right on either side of the bricks, and I don't want water to overflow there, only over the bricks so it stays in the channel).

 

[JamieB]

That could be done by making the area at the channel the lowest part of the wall, which would involve building the rest of it higher. It’d give you a nice waterfall if you built it right. I understand the urge to keep things small and simple, but I do believe you’ll fall in love and want to make it bigger later, so keep the ideas in mind for later. As for keeping fish in it, you want fish that are locals, native. That way if they escape, it’s no harm. Try talking to your local wildlife officer/ fish and game wardens. They might know of what would be good, and where to get some, but I know mine only stock game fish.

 

[j.w]

@zinjy I live in Washington also up north in Arlington and my pond has only ever gotten a couple inches or so of ice and rarely even that so I don't think you have to worry about freeze here unless you live on the East side of the mountains. I've got extra orange goldfish if you ever decide on those. Whatever kind of fish you put in there w/o a net or some sort of protection critters may enjoy lunch. I like @JamieB 's idea of adding sand to make it softer under all the other protective coverings.

 

[zinjy]

Yes, I'm on the west side and even in the coldest years I've never seen more than about 4 inches of ice on a body of water this big, usually much less, so I think it's deep enough even if I'm not able to raise the low end much. But I'm worried about UV damage to the liner that will be exposed if I can't raise the water level to cover more of the side on the upper end, what has full sun. This may be something that tips me back to epdm liners as they are apparently more uv resistant than polyethylene like what btl makes (they recommended I cover exposed liner to protect from UV). They recommended BTL 40 instead of PPL36, and are sending a sample. I will see if it's flexible enough for a pond this small. Another site that sells polyethylene pond liners like these only recommends them for larger ponds than mine, because of stiffness making it harder to form to the shape of the pond. This makes me wonder if I'll be able to bend it around the edges. The main appeal for me of the BTL polyethylene liner is being more puncture resistant to animal feet, but if I'll have to cover it with something else for UV protection either way on the exposed sloping sides, then that may take care of the puncture issue, and the price is similar.

Thanks for the goldfish offer! I would like to get native fish but there aren't many options it seems. I think the most likely native candidates for survival in a pond this size are Olympic mud minnows, but I haven't been able to find anyone that stocks them, so if I can't find any I might eventually do goldfish. The only way a fish is going to get from here to the creek is if a bird picks it up and carries it that far without eating it, which seems unlikely, so I don't think they'd get out.

 

[zinjy]

That could be done by making the area at the channel the lowest part of the wall, which would involve building the rest of it higher. It’d give you a nice waterfall if you built it right.

This does appear to currently be the lowest part, but it seems the while pond is at a bit of a slant so it would leave a lot of exposed liner at the upper end if I didn't make the concrete block part higher.

 

[addy1]

My liner the ppl36, has been sun exposed for around 9 years now. The stream is in full sun from the time it rises until almost sunset.
The stream runs on a timer so it is only water covered for a few hours a day. The liner looks as it did when I installed it (except dirt, algae etc)
It is not as easy as EPDM to curve around corners, (my stream has switch backs, so there are curves, drops, edges) It was not that difficult to install.
I did use epdm in the deck ponds, mainly because I needed just a small piece and the deer don't walk in them. Bought at Lowes. It slices a lot easier than the ppl and is a whole lot more slick. If I step carefully I can walk the length of my big pond without losing my footing, it is not like walking on ice.

 

[JamieB]

I’d say take a laser level, set it at the top of the slope so it sits even, then have a second person at the deep end to see where the light hits them to know just how tall the wall would need to be to retain water level. Or you could do a series of retaining walls that trickle into the main pool. If you’ve got lots of nice stone on the property, it’d be easy. My mind spins with the various possibilities. But, to start with, you first need to decide how you want to progress. Fastest easiest way would be smooth any cracks and gaps with sand, pack that well. Then decide on your underlayment, and liner. Before you put them in place, fix the retaining wall so it can be covered as well. That will prevent water just spilling at the edge instead of going over. You’ll want the edge of the wall just under the height of the pond edge, unless you expect heavy rains, in which case I’d suggest the wall be 4” shorter than the pond sides. The wider the spill way is, the less likely you are to have it overflow the pond at the sides. Next step will be to put your underlayment and liner down, then do a test fill using a garden hose. See what areas are left dry, and you can then decide if you want to do additional retaining walls, or cover with rock and plants. If that area gets frequent rains which will flood the area, rock and plants that don’t mind water are a good idea, but if you only get occasional rains and long periods with out rain, then simple rock only or potted plants may be the way to go. Be sure when you place the liner, that you secure the edges. A nice edging of heavy rocks will do it, pavers, bricks, etc.

 

[zinjy]

My liner the ppl36, has been sun exposed for around 9 years now. The stream is in full sun from the time it rises until almost sunset.
The stream runs on a timer so it is only water covered for a few hours a day. The liner looks as it did when I installed it (except dirt, algae etc)
It is not as easy as EPDM to curve around corners, (my stream has switch backs, so there are curves, drops, edges) It was not that difficult to install.
I did use epdm in the deck ponds, mainly because I needed just a small piece and the deer don't walk in them. Bought at Lowes. It slices a lot easier than the ppl and is a whole lot more slick. If I step carefully I can walk the length of my big pond without losing my footing, it is not like walking on ice.

That is good to know. The rep I talked to said BTL40 was their new recommendation over PPL36, but he recommended covering for UV protection, and said they warrantied for 20 years with UV protection and 25 without. Another site that sells both kinds of liners indicated epdm was more UV resistant but it seems both are recommended to be covered. I haven't received the sample yet so maybe that will help me decide. Have you ever had to repair a tear in the ppl? I was wondering how that compares to patching epdm.

 

[zinjy]

I’d say take a laser level, set it at the top of the slope so it sits even, then have a second person at the deep end to see where the light hits them to know just how tall the wall would need to be to retain water level. Or you could do a series of retaining walls that trickle into the main pool. If you’ve got lots of nice stone on the property, it’d be easy. My mind spins with the various possibilities. But, to start with, you first need to decide how you want to progress. Fastest easiest way would be smooth any cracks and gaps with sand, pack that well. Then decide on your underlayment, and liner. Before you put them in place, fix the retaining wall so it can be covered as well. That will prevent water just spilling at the edge instead of going over. You’ll want the edge of the wall just under the height of the pond edge, unless you expect heavy rains, in which case I’d suggest the wall be 4” shorter than the pond sides. The wider the spill way is, the less likely you are to have it overflow the pond at the sides. Next step will be to put your underlayment and liner down, then do a test fill using a garden hose. See what areas are left dry, and you can then decide if you want to do additional retaining walls, or cover with rock and plants. If that area gets frequent rains which will flood the area, rock and plants that don’t mind water are a good idea, but if you only get occasional rains and long periods with out rain, then simple rock only or potted plants may be the way to go. Be sure when you place the liner, that you secure the edges. A nice edging of heavy rocks will do it, pavers, bricks, etc.

Thanks for the ideas! I don't have a laser level but will try again with a regular level to get a better idea of where the water will hit, when I estimated before it seemed pretty low. We do get heavy rains here, but 4" exposure would be fine if I could achieve that, and could be covered by overhanging plants. The soil is mostly clay unfortunately but I have been gradually accumulating rocks as I find them, there are a few places around here where they get exposed from underlying basalt or just fall out of clay hillsides, or I pick up from the rivers. I'd love to get some more big rocks but ordering some for delivery isn't really in budget right now, so that will take some more time. I'd like to get the liner in first to take advantage of the spring rain and water abundance before we hit the droughty summer time.

 

[JamieB]

Road trip! To the local river/ lakes with you, to gather a few nice rocks every time. I’ve got clay, silt, loam, sand, and the rock that’s put on the road. So to get rocks, I have to road trip too. I’d say if you’ve got a truck, go road trip dirt roads to look for good ones. If you can get a long board, it could be laid from the high edge of the pond to the deep end, with someone there to lift it till it’s level, to see how much higher the wall would need to go.

 

[JamieB]

As for looking for rocks, if you wanted to make the wall look rock, you could coat it in waterfall foam, let that cure, then carve it to look like rocks. Some nice flat rocks along the top that overhang to the far side will make a nice waterfall, and the foam would keep them set in place.

 

[addy1]

Have you ever had to repair a tear in the ppl?

I have not been gentle with the liner, it has never torn. No matter how many deer walk on it. I used the same liner in Arizona, it too did just fine. There I had coyote, owls etc bathing in the stream.

I had a huge edge rock get knocked in over the winter, one that will be heavy to lift back out. No torn liner issue. I need the water to be warmer to go swimming to get it. Might need abused husband to lift it back out.