Pond liner attached to boulders


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I have a medium sized pond with two very large boulders. I'm still in the digging part, and I'm getting reading to install the underlayment and liner. Since I do not want the liner to be visible, once the water is in, has anyone ever affixed a pvc liner to rock? I'm open to fish friendly adhesives, masonry screws and some sort of gasket or some other method. Thanks much for your time.
 

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Mmathis

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Hello and welcome! Those are awesome boulders! Are you wanting the boulders to stick up, like islands, with liner attached all around? I have no idea, but am sure someone here can give you suggestions. If you haven’t already purchased the liner, I would recommend HPDM over PVC, especially if you are going to have to manipulate the liner quite a bit.
 
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Thanks much. And yes on the boulders being above the water line.
 
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I second the no PVC liner. I hope you haven't bought it yet. If you have, I would return it. I can tell you from two very bad experiences that PVC liners are terrible. They dry out and crack literally within months. They are also very easily punctured. I know the lower price is tempting, but trust me...don't use pvc.

The usual go-to liner material recommended by most is EPDM 45 mil. Then there's HDPE and HDRPE the R meaning reinforced. EPDM usually requires an underlayment, whereas the other two usually don't. EPDM is a more flexible thick rubber akin to a tire inner tube. The other two are much stiffer.

The liner is the very basic part of your build and you don't want to dismantle the whole thing because of a leak or tear. Not to mention that leaks are usually very difficult to locate. And if you have fish and plants, you'll have to rehome them while you install a new liner.

My original first pond about 12 years ago was a pvc liner. It was built in late Summer. By the middle of Winter it was leaking 300 gallons per week. All Winter I was adding 300 gallons every week until Spring came when i was able to change to EPDM. For my recent bog filter build, I used HDRPE.
 
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Oh! Great job you have done there! You carved all that soil out nicely!
You have quite a dilemma there with those boulders and the liner. If only the boulders were higher that the level of the water. Basically, the boulders sitting on a soil island that is higher than the water. That would be the best scenario. Is it too late to lower the whole site to make islands above the water level?
 
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I think trying to adhere the liner to the boulders is a bad idea and maybe hard to camouflage if it were even possible.
Keep the water level below the soil that supports the boulders. Run the liner up on the dry soil up to the boulder and pile rocks on it to cover it up.
 
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Sorry for so many posts! I'm still thinking about your dilemma.
Looking at your picture again. You can easily do this. Just add soil to the area around the boulders. Build it up higher than the water level. Pack it down good. And as I said in my previous post, run the liner up on that high and dry island right up to the boulders. Stack stones on the dry liner to hide it. No glue or any type of adhesive. Just get that liner edge above the water.
 

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If it were me I would use a chain falls hoist and tripod (or rig something similar up), with straps to lift the rocks and slip the liner underneath so the rocks are sitting in the pond. Be sure to leave slack in the liner so when water is added it doesn’t Pull tight and tear, as well as adding some underlay material between the rock and liner.

As poconojoe said it is going to be hard to maintain a seal otherwise, as the various materials will expand and contract at different rates causing leaks.
 
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I agree with lifting those rocks. I would do anything in my power to get the liner underneath them. Then you have a really cool situation. Otherwise I think you have a really big challenge!
 
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I would never have mentioned it myself, but since it’s been stated....I was going to suggest raising the boulders and slipping liner underneath. I have no idea what that would involve, though.
 

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@Falcon 7
I vote raise and put in liner underneath. With extra piece of liner or two on top of regular liner for extra protection.
 
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I would also have the liner under the rock. You could lever the rock up on some blocks and lay the liner rolled of against the block and then move the block onto the liner, unroll some more and move the other block. I would layout the liner so you will have it in the right place when you place it under ht e rock. It can be done with blocks and 6'pry bars. Don't ever place the fingers under the rock when on the pry bars, always have the cribbing secure before you reach under. We used to play dice with 36" blocks of concrete with Urban Search and Rescue. The secret is lots of cribbing blocks ,2x4 and 4x4 as well as a few wedges. If you where close by I would love to help, would be fun.
 
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All this lifting of boulders...no disrespect, but that's crazy! Those things are going to be freakin' heavy! There's really no place to use a pinch bar. Where are you going to place a fulcrum? And the ground around the boulders is just going to collapse if you place any force on it.
You're going to need a crane or at least a gantry with a chain fault and a few good slings. There's really no place on the house side to stand the leg of a gantry anyway.

Just do it the easy way, like I said...build up the soil around the boulders higher than the water surface is going to be. Cut the boulder shape out of the liner. Drop the liner over the boulder and onto the soil you just built up. Wah lah...the cut part of the liner is higher than the water. No chance of leaks. Cover the exposed liner with rocks. Done.
 
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Others have tried to seal a liner to rocks below the water line , have not heard of good results. I think his idea is to have the bottom of the rock below water.
 
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Definitely not easy, but it could be done. Especially with a chain falls hoist, might take some creative thinking. I work with rocks this size and bigger just about everyday and have moved them With come-a-longs, chain falls, would definitely not get under it though.
 
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I can see why so many advise lifting the boulders but it’s where they are located that would make that a gargantuan, if not impossible, task. I would have to agree with poconojoe on this....build up the soil, cut out for the boulders and cover with rocks.
 
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Thanks for all the good ideas. For now, I plan to cut the liner around the rocks and hide it with smaller ones. Since I'm not going for a natural look, but a Japanese design, I should be able to ornamentally hide the liner edge with nice stone and plants. I'm expecting the kit to arrive today, so, more photos to follow. Thanks again to all.
 
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Thanks for all the good ideas. For now, I plan to cut the liner around the rocks and hide it with smaller ones. Since I'm not going for a natural look, but a Japanese design, I should be able to ornamentally hide the liner edge with nice stone and plants. I'm expecting the kit to arrive today, so, more photos to follow. Thanks again to all.
Just make sure the cut liner is significantly higher than the water level.
 

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