What underlayment to use over old concrete?

[zinjy]

There is an old concrete former pond constructed in my back yard and I would like to make it hold water and be a wildlife pond (maybe some small fish to help with mosquitos, but it's quite shallow: about 15X25 and between a foot and a foot and a half deep). The pond has not held water in my lifetime, because the concrete is old, very irregular, somewhat crumbly in places, and has giant cracks and broken bits, so my plan is to use a liner (probably epdm) to make it watertight.

The question: What is the best underlayment to protect the rubber from the rough concrete? There is a type of geofabric sold along with liners at pond stores, but this seems to be primarily hold back the dirt and protect from roots and burrowing animals, and I don't know if it would work well in this case. What I need I think is more of a padding between the rubber and the concrete: animals will not be able to burrow through the concrete and there are no tree roots getting through the cracks in the concrete (though there are weed roots persisting in the cracks that need to be smothered and not grow through). I want to be able to walk in it when necessary (and prevent damage if a large dog gets in there which will probably happen at some point) without puncturing the rubber against sharp bits of concrete. I also don't want anything that's going to biodegrade and invite ants to live under the liner, hence why I am not smoothing the irregular parts with dirt. Old carpet has been suggested but I don't have access to any (and I don't know if it would be the best option), though I do want something cost effective, since the rubber liner is already fairly expensive.

Ideas for underlayment in this situation? Has anyone done something similar?

 

[addy1]

I had a lot of sharp rocks in the dirt once I dug the pond. I bought carpet liner, the cheapest, and used it.

The heavy duty tarps at the stores might just do the job.

Welcome to our forum!

 

[mgmine]

I used an old swimming pool liner which is very thick. On top of that, I used an old carpet. Every week I see old carpet at the curb. I'm sure you could also go to a carpet store and pick some up from a job they have done. There is no value in it so it always gets thrown out. Be sure to check it for staples and tacks. The pool liner is harder to find but check Craigslist as well as pool companies.

 

[poconojoe]

I suggest carpet padding, then the standard underlayment, then your liner. From experience, I would use nothing but EPDM liner. Stay far away from PVC liners. Carpet padding (rebond) is pretty thick and won't break down. You can obviously get it at a carpet store, but the big box stores (Lowe's, Home Depot) also sell it. The standard width is 12 feet. The cheapest one is 40 cents a square foot.

 

[j.w]

@zinjy I've used carpets, blankets, any kind of soft padded cushy stuff. Pile it up good over any really sharp area's or better yet get rid of the sharp pointy stuff.

 

[zinjy]

Thanks for the replies! I am probably going to use an epdm liner on top, in part because it needs to be flexible enough to go around the rough raised edges of the concrete pond. The edges are another area I think I need to pad because they are so rough. I did try breaking off some sharp parts but it just breaks into more sharp parts.

Is the geofabric type underlayment sold by pond stores not protective enough for this application? I don't know if it would be enough padding. I do have an old tarp but it's also worn in places from sun exposure.

Those who used carpet padding, how thick of padding did you use? The carpet pad I've seen under actual old carpet seems to be made of composite bits that fall apart over time... Has that been an issue? Or do you mean a different kind of padding that is like a continuous sheet of rubber foam?

( If you can link to an example that would be great, there are so many options I've gotten a bit overwhelmed with research and stalled at the underlayment stage!)

 

[addy1]

The carpet pad I've seen under actual old carpet seems to be made of composite bits that fall apart over time... Has that been an issue?

It is under the liner, under water, so I have no clue if it has fallen apart. The bits I can see here and there all seem fine so far. I do not recall what thickness/type I used.

I used liner from bend tarp and liner in Oregon. It has survived a trapped deer's hooves digging in to try and get out of the pond, deer walking in the stream, my large side rocks being knocked in by the deer.................some tough stuff. They said I could install without padding, but I decided to use padding anyways. You can see it to the right, the bog was newly laid groomed dirt so it did not need padding.

 

[zinjy]

It is under the liner, under water, so I have no clue if it has fallen apart. The bits I can see here and there all seem fine so far. I do not recall what thickness/type I used.

I used liner from bend tarp and liner in Oregon. It has survived a trapped deer's hooves digging in to try and get out of the pond, deer walking in the stream, my large side rocks being knocked in by the deer.................some tough stuff. They said I could install without padding, but I decided to use padding anyways. You can see it to the right, the bog was newly laid groomed dirt so it did not need padding.View attachment 119541

Deer hoof protection would definitely be good, thanks for the suggestion!
Do you remember which version of liner you used? I see they have several options on their site. Is it flexible enough to fold over a rim (the concrete pool has a jagged rim about 2.5" thick that I'll need to fold liner over)?

 

[addy1]

I used ppl36, not made with that name anymore, just give them a call they will help you with what you need.

Mine is folded, has curves etc. Not as flexible as epdm, but also no way as slick as epdm, once it has been in the water for awhile.

 

[zinjy]

I used ppl36, not made with that name anymore, just give them a call they will help you with what you need.

Mine is folded, has curves etc. Not as flexible as epdm, but also no way as slick as epdm, once it has been in the water for awhile.

Thanks, I sent them an inquiry with a description to see what they recommend for my situation as an equivalent to ppl36. I'm not averse to EPDM which seems very popular, but I am concerned about it springing leaks as this seems to be a common issue (for instance I am sure the neighbor's large dog will probably get in there when I am not around and then scramble out at least once...)

 

[JamieB]

I’d personally be removing the old concrete, and using the hole where it was. Ponds are addictive, and ease of adding on, going bigger is something I’d look at. But if you don’t intend to add fish, and just want to make it hold water, you could remove the bad concrete, patch it, then use aquatic safe epoxy if you can’t get the liner you want.

 

[zinjy]

I’d personally be removing the old concrete, and using the hole where it was. Ponds are addictive, and ease of adding on, going bigger is something I’d look at. But if you don’t intend to add fish, and just want to make it hold water, you could remove the bad concrete, patch it, then use aquatic safe epoxy if you can’t get the liner you want.

I may eventually add (small) fish down the line in hopes of controlling the inevitable mosquitos (I'd like to add native ones, but having a hard time finding a source). I considered trying to waterproof it, however, this concrete is so old and decrepit I don't think it could be made watertight reliably, and if I did, it would probably crack again in a freeze. All of the concrete around the house (patios, etc) is cracked in places due to freezes or ground settling. As far as removing it goes, the pond is in the middle of a whole concrete construction involving a waterfall-like thing, a long spillway channel, bridge, etc. which are connected together, and also the concrete pond is partially supporting a very large rhododendron that takes up most of one side (which I don't want to harm), so removing it isn't really a good option in this situation.

 

[addy1]

(for instance I am sure the neighbor's large dog will probably get in there when I am not around and then scramble out at least once...)

We had our neighbors sheepdog get stuck in the pond, huge, old and could not get herself out. I could see where she clawed trying to get out but again no damage.

 

[mgmine]

Animals (or kids) falling into the pond is certainly something to keep in mind. For that reason, it's a good idea to make the pond floor slope. If the bottom is flat I would add dirt so that it's easy to get out at one end.

 

[zinjy]

Animals (or kids) falling into the pond is certainly something to keep in mind. For that reason, it's a good idea to make the pond floor slope. If the bottom is flat I would add dirt so that it's easy to get out at one end.

It's quite sloped, in fact so much that it's easy to slide in even with the concrete. I might put some rocks there after the liner is in to make it harder to slide down.