Cement Backer Board

[vestaviascott]

Liner. Anywhere that has a seal has the possibility of leaking.
Although I don't know about the backer board, it would be the joints that would concern me.

Thanks. I agree. I'm leaning towards a hybrid approach. Perhaps lay the liner in, then the hardibacker board would go over that (to help hide the wrinkles in the liner and the liner itself).

Or perhaps the reverse. Using the hardibacker as a support for the dirt walls (the long walls are dirt and the shorter ends are 8 in concrete blocks), then laying in the liner over that. Especially the dirt wall I cut in under the existing patio - The idea is to allow the pond to disappear under the edge of the patio (about 6 inches). The cement board would allow me to wrap the top of the liner over it in order to secure it there under that edge.

 

[tbendl]

The weight of the water should be sufficient to hold the walls. I am unfamiliar with that type of board and would be concerned about it leaching chemicals into the pond. You were planning on fish?
Really to get a "seamless" look, I would think you'd have to concrete and seal it.

 

[sissy]

I know the stuff when you cut it it is really rough .I have gotten lots of cuts from it .They have red guard product but it turns pinkish color after it dries or sometimes darker red

 

[vestaviascott]

The dirt wall under the patio has pits and valleys and lots of jagged slate rock sticking out - it would distort the liner by a great deal and make the corner folds near impossible to even out.

I will be using a thick underlayment under the rubber liner, but the the main purpose of the hardibacker, along this wall, is to provide a way to terminate the liner on this wall (on all other walls, the liner can be terminated with the cap blocks laying over top of it, however, on this wall, that's not possible. It will also even out the voids and protect the liner from the jagged rock.

Good point. The Red Guard waterproofing product does dry red which is a non starter for a pond (or at least, this pond - I'm sure there may be such a thing somewhere). Unless it can be tinted to black or will accept a color coat, it will not be considered. But using it below the liner, as described above, would be fine with me.

 

[sissy]

You could use the thick foam insulation stuff .It comes in 2 inch thick and holds up .

 

[vestaviascott]

You could use the thick foam insulation stuff .It comes in 2 inch thick and holds up .

I'm not sure I know what you are referring to. Do you have a link or more info on the trade name of the insulation that can withstand ground contact?

 

[sissy]

It is sold at lowes and home depot .It can withstand ground contact .It is around 30 dollars a sheet but it holds up to lots of stuff