Sealing Porous Coral Rock for Waterfall

[NiftyFifty]

Has anybody had success with sealing coral rock? I’m not sure if I’m posting this in the right place. Maybe I should attach it to my original post about my pond?

Anyway, I just realized that the rocks for waterfall I am rebuilding might actually be coral. I assumed they were lava stone because we are so close to Idaho (I’m in Salt Lake City, Utah).

Over the last 2 weeks, I’ve been placing the rocks for the waterfall. It’s taking me forever because I’m moving them myself. At any rate, last week it occurred to me that even though these rocks were used in the original waterfall, I should test them to see how the water runs on them. Much to my chagrin, the rocks are like a sponge! How in the world was this ever a functioning waterfall with these porous rocks???

As I said, I had assumed I was dealing with lava rock, but during my experiment with running water over the rocks, I thought to carve out a bowl and trenches in the rock to see how difficult it would be to carve where I needed to. I was puzzled because the rock was so easy to dig into. Then it hit me — this might be coral rock.

As an experiment, I covered the bowl I carved out of one of my rocks with sodium bentonite. With a thick enough layer of clay, the water doesn’t seep through the stone, however, once the water evaporates, the clay cracks and water runs through the cracks in the clay. I guess you have to keep it wet for the sodium bentonite to work?

So, I’m desperate for suggestions for sealing the rocks so that water will run over them rather than soaking into them.

Thanks!

 

[Lisak1]

I think you’re fighting a losing battle to be honest.

Can you post pics of the original waterfall?

 

[j.w]

Has anybody had success with sealing coral rock? I’m not sure if I’m posting this in the right place. Maybe I should attach it to my original post about my pond?

Anyway, I just realized that the rocks for waterfall I am rebuilding might actually be coral. I assumed they were lava stone because we are so close to Idaho (I’m in Salt Lake City, Utah).

Over the last 2 weeks, I’ve been placing the rocks for the waterfall. It’s taking me forever because I’m moving them myself. At any rate, last week it occurred to me that even though these rocks were used in the original waterfall, I should test them to see how the water runs on them. Much to my chagrin, the rocks are like a sponge! How in the world was this ever a functioning waterfall with these porous rocks???

As I said, I had assumed I was dealing with lava rock, but during my experiment with running water over the rocks, I thought to carve out a bowl and trenches in the rock to see how difficult it would be to carve where I needed to. I was puzzled because the rock was so easy to dig into. Then it hit me — this might be coral rock.

As an experiment, I covered the bowl I carved out of one of my rocks with sodium bentonite. With a thick enough layer of clay, the water doesn’t seep through the stone, however, once the water evaporates, the clay cracks and water runs through the cracks in the clay. I guess you have to keep it wet for the sodium bentonite to work?

So, I’m desperate for suggestions for sealing the rocks so that water will run over them rather than soaking into them.

Thanks!

Wondering if there is some kind of a sealing spray that is not harmful to the water? Just guessing but it seems like something like that might work. I just looked online and this seems to be pretty impossible for what you want to do. But then, never say never!

 

[NiftyFifty]

I think you’re fighting a losing battle to be honest.

Can you post pics of the original waterfall?

Noooooo-oh!
Here’s the original waterfall, top right portion of photo

It looks like they had some mortar slathered between some of the lower rocks.

 

[NiftyFifty]

Wondering if there is some kind of a sealing spray that is not harmful to the water? Just guessing but it seems like something like that might work. I just looked online and this seems to be pretty impossible for what you want to do. But then, never say never!

I just gotta make it work — so I’m not saying never yet.

I’m carving out channels where I want the water to travel. I experimented using sodium bentonite in the channels. I read that people use this to fix leaks in ponds. However, I discovered that when the clay dries out, it cracks and water can seep into the cracks. I am assuming that the bentonite has to stay wet all the time for it to work?

I like your idea of sealing spray as I would really only need to seal the channels where the water travels. I’ve seen sealing spray for terra cotta, maybe I’ll give that a whirl? Or maybe I can slather cement or some other sealant in my channels?

I was not planning on mortaring anything until I had the pond and waterfall functioning for a while, just in case I need to change anything. But maybe I just cement the channels for now.

 

[NiftyFifty]

For what it’s worth, this is what the rocks look like up close

Hey! I just had an idea. I wonder if penetrating sealer would do the job. My dad used to use that on coral pavers that we had in the Bahamas when I was a kid. Has anyone ever used that? I only watched him apply it, and that was a long time ago.

 

[j.w]

For what it’s worth, this is what the rocks look like up close View attachment 166150View attachment 166151

Hey! I just had an idea. I wonder if penetrating sealer would do the job. My dad used to use that on coral pavers that we had in the Bahamas when I was a kid. Has anyone ever used that? I only watched him apply it, and that was a long time ago.

I hope you figure it out!

 

[Lisak1]

I mean, if you fill ALL the gaps with waterfall foam and if you get water pouring fast enough over the rocks, you'll have a waterfall. But if your goal is to keep the water from seeping into the rocks - I'd give that one up. Even granite will absorb water - all rock is porous to some degree.

One concern I would have would be cracking if the rocks fill with water and then freeze. This is a small waterfall - why not just get some different rocks?

 

[NiftyFifty]

It’s pretty big

 

[NiftyFifty]

I got the waterfall working!

My solution for preventing all of the water from soaking into the sponge-like pores of the coral rock of the waterfall was to put pond liner where the water flows across the waterfall. This is not a permanent solution, and it doesn’t look great, but it allows me to run the waterfall for now.

This upcoming summer, I plan to remove the liner and try slathering cement in the divots I carved into the coral rock to direct the water flow.

Some of these rocks are huge and I couldn’t really afford to buy different rock for the waterfall so I had to reuse these. Plus, the old waterfall was made using these coral rocks, thus I figured they would be suitable to re-use in the refashioned waterfall.

As for these porous rocks possibly crumbling during the winter where water gets into the pores, that’s totally a legitimate concern. However, I believe these coral rocks were used in the original waterfall and have been here in my yard since the pond was made at least 50 years ago. I don’t know why they haven’t been damaged during the freeze thaw cycle, but they don’t show sign of damage.

 

[Lisak1]

Define “pretty big”. From the photos.(which can be deceptive, I know.) it appears you could rebuild this waterfall with a handful of large two man boulders. But if you want to stick with the rocks you have then I hope it works out!