Above ground pond construction with liner - finishing the top

[lidiam]

Hello

I'm building a two pond system: a tiny, above ground pond, roughly 2' x 5' (and 2' deep) and in the ground pond, yet to be dug out, roughly 10' x 5'. I have ducks and the larger, in the ground pond is for their use. I've had an above ground hard shell pond and in the ground kiddie pool for them for several years, till the hard shell pond cracked a few months back. I decided to replace it with something more permanent. The upper pond was holding water hyacinth as filtration.

I'm attaching photos of the above ground pond construction (cinder blocks with steel stakes and rebar). I filled it with some soil to make it two level and added sand. I have underlayment and EPDM liner ready, however, now I'm not sure how to proceed...

I want to use a large, natural, flat-ish stone and have water fall off of it and over more rocks to the lower pond. The 'waterfall' stone is about 2'' tick and quite heavy. I'm thinking of adding a layer of about 3"- 4" of mortar around the pond wall, apart from the "waterfall" section. I would then put the underlayement and liner over the lip of the pond wall. The "waterfall" rock would also go over the liner, although I'm not sure how to attached it. I've seen posts saying that mortar won't hold it. Would I need to glue it in place? Any waterfowl safe glue? I presume liner has to go over the lip of the waterfall so that water does not seep in, between the liner and cinder blocks. Am I correct here?

What is the best way to attach liner to the pond wall? I found some posts suggesting embedding pieces of wood in the mortar at the top, so that liner can be nailed to them. I like this idea. My pond wall is 3.5" tick - is that enough to hold the wood with nailed liner in place? I have 1"x1" redwood - will that work? I presume this upper layer of mortar will not give in under the pressure of water (without any reinforcement) - there would probably be about two inches of water held by the mortar wall - is that ok?

Lastly, is underlayment enough to protect liner from the rough cinder blocks? My pond is not rectangular, so edges of cinder blocks are sticking out a bit, pretty much everywhere on the inside of the wall. Do I need to add a layer of mortar on the inside, to cover all the edges?

Thanks
Lidia

 

[Lisak1]

Nailing liner to a board seems risky - and pressure on the liner and I feel like it would rip because you've created a weak spot with a hole. And I have no idea if you can mortar wood to a wall and hope for it to stay in place. Sounds like you're mixing mediums there. Hopefully someone will have some better ideas for you.

 

[lidiam]

After more research I decided to change my approach. I'm not going to build the pond up any more, but cut the opening for the spillway in the existing wall (no rebar on that side, since it's concave, it should be structurally ok). I'll see if I can attach strips of wood to the inside half of the top of the wall and then attach liner to that. I should be able to add some mortar on top, as it should bind to the other half of the top of the wall.

I curious if anyone has any advice on cutting and gluing the liner to better fit the shape of my pond. As it it, there will be many folds in the corners. I found this thread elsewhere, and see that people tend to cut out corners so that there are no folds: https://www.koiphen.com/forums/showthread.php?143212-Topping-off-a-concrete-block-liner-pond. Personally, I would prefer not to cut liner.

 

[Lisak1]

Interesting. I have no idea how they get that tight fit with liner. Even with a perfectly square pond, you would have excess liner at the corners. I know how to cut fabric to line a box, but you aren't worried about leaking corners in that case.

Maybe someone else here would know!