Try searching my name - madtripper. I asked the same question last fall.

It was about split between black foam and special cement. I ended up using the cement an dreally liked it. I think the foam would make a mess as it expands. It also gets on everything if you are not careful. I also used the cement to add extra height ot the edges of the spli rocks, forcing water down the center. The cement has the same color as the rocks - or close to it. Black foam could not work for this.

madtripper,

Did you get the cement to adhere to the liner? I did a test of this and it seemed rather easy to free the liner.

I agree about the negatives on the foam, but it does adhere well to the liner.

Thanks,

Bob

You are right, the cement does not adhire very tightly, but I think once the seal is made, and small cracks will be filled with dirt.

I've used the black foam and it is a pain to work with. If you use it, be sure to wear old clothing and rubber gloves. Then plan on using twice as much as you expected.

The things I like about the foam is that it's still there after ten years. I think it will be there after a hundred years. You can also pull the liner apart from the stones without harming the liner. I've rearranged my waterfall a few times and never had trouble pulling it apart.

I've also used construction adhesive to secure some of the stones in my waterfall and I needed a large pry-bar to get that apart.

johnkr,

In my experiments, I had the most success with the foam.

I have an undulating flat stone, very neat looking, I have it set so the water will pool toward the back and run over the high edge into the pond. Then the water falls from the level above into the pool at the back of the lower stone...

What I'm uncertain of is will the seal definitely be good enough to prevent water flow between the back of the stone and the liner?

I was thinking about the construction adhesive too.

There was a a former member of this forum, who found 'Gorilla Glue' stuck just about anything to everything.
It is pretty expensive and does not have a long shelf life once the container is opened, from what I have read about it, but it is supposed to be a terrific glue.
I have not tried using it myself, but the guy who posted the information was quite pleased with the outcome.
"Horton"

Bob, I had a problem with water flowing under my waterfall and out the back of a small stream that runs from my biofilter to the falls. Don't ever expect water to flow down hill or take the easiest path.

I used some aquarium glue to seal rubber liner to a piece of plexiglas and it's been leak free for the past two years.

madtripper, what is this "special cement" called? do you remember? thanks

I'm guessing it was probably hydraulic cement.