Securing stone to EPDM liner

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Greetings!

I've been perusing the blog for a few days; I haven't found details about this particular issue.
I'm rebuilding a failed pond, and the new version is about 1700-2000 gallons.
I have some stone (pictured) that will line the walls after the liner is placed.
I think there is enough angle to the walls and squareness to the stone, that they may just stack in place and stay there, but I think it would be better to secure them to some degree.
Has anyone had experience in this type of situation using pond foam polyurethane to adhere stone to the liner walls in what will be a bit of a steeper arrangement?

If the foam secures it sufficiently, I will do that, otherwise might use a little portland between layers of the rock near the liner.

Thanks so much in advance for any thoughts about this....
 

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My question is why? You realize those blocks will soon be covered in algae and look like every other surface in your pond. If you want to keep the blocks free of algae, it would mean A LOT more work for you to keep them scrubbed clean.

What size are the blocks?
 

j.w

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@stillgotomx

I only put rocks on my shallow ledge shelf and up above them to hide the liner. Can't see much down deep due to the nice carpet algae that is good to have on the sides of your liner. Think after awhile the blocks won't be visible much.
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Very nice pond. Thanks to both for your thoughtful insights. But my question is really not whether I should do it this way; I am specifically interested in the question of the strength and durability regarding adherence of the submerged stone to the liner.
 

Mmathis

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Hello and welcome!

I can’t answer your question (for your intended purpose), but ponders do use things to secure rocks in waterfalls. I don’t think the pond foam is intended to be structural. It’s mostly for filling in gaps to help water flow where you want it to flow. There is a roofing sealant that a lot of us use that has a lot of good applications for use in a pond. Not sure how structurally secure that would be, though. It’s Locktite PL for roof and flashing (it says it’s not for underwater use, but we all use it without problems).

So, you’re just wanting to be sure the rocks will stay in place, and not move around? Horizontal stacking (as in the look of a ledge), or vertical stacking (as in having them face a side or wall of the pond)?
 
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Hello and welcome!
I can’t answer your question (for your intended purpose), but ponders do use things to secure rocks in waterfalls. I don’t think the pond foam is intended to be structural. It’s mostly for filling in gaps to help water flow where you want it to flow. There is a roofing sealant that a lot of us use that has a lot of good applications for use in a pond. Not sure how structurally secure that would be, though. It’s Locktite PL for roof and flashing (it says it’s not for underwater use, but we all use it without problems).

So, you’re just wanting to be sure the rocks will stay in place, and not move around? Horizontal stacking (as in the look of a ledge), or vertical stacking (as in having them face a side or wall of the pond)?
Hi thanks.

Yes, the walls are angled outward some, and the stone may very well stay in place vertically when stacked against it, but I am thinking about securing them further to keep them in place. When I demo'd the old pond, I was surprised at how much mortar they used, mostly along the edges, and how very adherent it was to the EPDM.

I was just wondering how far one could "push it" for securing the stone against the fairly-vertical wall with the polyurethane. I wasn't worried at all about the idea of using along the pond edges, which are flatter. I guess my question is how well it sticks-and-stays-stuck underwater over time.
 
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i have used the waterfall foam to secure rocks on a sloped wall in my pond. but they are not a 1/3rd the size or weight of your slabs. The foam while it does stick it is not very strong but like if you have ever bought something that cam packed in a spray foam container it does SQUEEZE / suround the item very well and it can lock it up. However our asking to use it as a glue and as a glue i say it is not strong enough, you have uniform edges that have very little detail for the foam to lock it up.
Mortar is a superior product as far as strength is concerned and as it seems you may already know adding an extra scoop of type s Portland cement will make it even stickier.

what i can suggest is to try and build your boulders as close to the shape of the excavation as you can . but instead of filling it with tons of mortar, pull the liner in to the stone and back fill with sand or native soil if it's not filled with rocks. Fill up most of the space then use a creamy mortar to fill in behind it. In the long run having this area as small as possible will reduce any build up of sludge.

Unfortunately your walls are close enough to being vertical if some kid was in the water they could pull the rock over, and regardless mortar or foam they may pull over a small section which could hold them under water if it toppled on them.

i assume your installing these standing these so the long way is up
 
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Thank you sir....very helpful and informative. I get exactly what you mean about packing in behind the liner. I will lay these in lengthwise horizontally. Some have the same height and depth, others are about a foot broad, so I plan to stagger them some, allowing for various interlocking configurations in the wall, which should help stablility, too.

Much appreciated..
 

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