River Rock under Pond Liner

[MoonShadows]

While the forecast does not look the best for next week, the snow has melted, the ground has softened and temps are beginning to moderate. So, I plan on setting up my hexagonal redwood raised pond. It is 425 gallons and has a preformed 45 mil EDPM liner. I want to create a border of about a foot or so wider around the pond with river rock held in by 4" wall block. I want the pond to be at the same level as the river rock border, so I was planning on filling the whole area with river rock. My question is can I set the liner on the bottom pad on top of the river rock? The liner pad that came with the pond is really nothing more than foam packing material about 1/8 of an inch think. The river rook is smooth with no sharp points. Or, should I put down more padding before I put down the liner?

 

[addy1]

Most likely ok, but I always over do everything. If it was mine I would add another layer.

 

[Lisak1]

I would actually skip the rock under the pond. There's really no reason for it to be there, and the chance of friction rubbing a hole in the liner would haunt me. Don't ask me how that would happen - it would just plague my brain. Why not let the liner go a little deeper? Bonus - more water!

 

[MoonShadows]

The liner is preformed and fits to the height of the pond frame, so I don't want it to sit low. I know there is really no reason to have the river rock under the pond, but I already have the rock, and if I build up the soil to the level of the perimeter that will be river rock, I am concerned of soil migrating out into the rock over time.

 

[Meyer Jordan]

My concern would be that the pond would settle over time and end up askew and un-level. How thick will this layer of river rock be?

 

[MoonShadows]

About 4 inches with an approximate underlayment of 2" of screenings (rock dust).

 

[addy1]

I used rock dust when we dug a hole for our propane tank. That stuff becomes like a rock. Also put some under our 1000 gallon stock tank it has kept it stable for years now. I used about 2-3 inches of it.

 

[MoonShadows]

Yup, we used it for the floor of our greenhouse. Last fall I put slate on top. Didn't finish it until just recently. Couldn't believe how hard the stone dust gets. It packs real well.

 

[Meyer Jordan]

About 4 inches with an approximate underlayment of 2" of screenings (rock dust).

View attachment 98271

Yes, you can achieve good initial compaction with rock dust, but I am not sure that the gravel can be manually compacted enough to support over 1.5 tons of water and remain stable.

 

[MoonShadows]

What if I did just rock dust right under the pond (I have 5 cubic yards sitting in my driveway) and then rock dust topped with river rock on the border that will be around the perimeter of the pond...so all that water weight will be sitting on compacted rock dust?

 

[addy1]

I would just do the rock dust. It does compact hard.

 

[Meyer Jordan]

I agree with @addy1 . This would seem to be the prudent action.

 

[MoonShadows]

Sounds good @addy1 and @Meyer Jordan . Thanks

 

[MitchM]

The only thing that would cause the base to shift once it's in place is if moisture was to enter under the liner.
Make sure you have the base sloped so that surface water runs away from your pond structure.

 

[Lisak1]

Ooooohhh! Preformed liner. Different story!