Stacked Granite Slab Waterfall

[opnorty]

Hello everyone-
First, I am really new to this forum and building garden ponds/waterfalls, so I apologize in advance for my crazy questions and long post.

I have a spot in my yard that really needs help. We have a concrete retaining wall off the end of our drive that is essentially an extension of our house foundation. It is cast in place concrete with the fake brick form liner. Ickkk. I have a friend that works for a granite countertop company, and they have about a pickup load of scrap/waste granite slabs a week they just throw in their dumpster. I have been collecting these for about a month now and have a pretty good stockpile.

My ultimate plan is to break these slabs up (all 3/4 inch thick) so they are from 4 inches to 12 inches in width. I am hoping to stack them up with the rough edges showing, slanting from about 12 inches wide at the bottom to about 4-6 inches wide at the top. I am planning on using some 6" wide pieces to form a pond area at the bottom. Overall, the wall is about 9 feet wide and 7 1/2 feet high. I am hoping to have the pond at the bottom be about 18" deep so the wall is also a sitting wall. I will be putting a pump in a sump pit and piping the water to the top. My idea is to use a piece of vinyl gutter along the top, with the outlet from the pump emptying into this to form the level weir at the top. I am planning on starting to stack the granite down at the footing elevation of the retaining wall, "gluing" it together with silicone, and tying it back to the wall with brick ties.

From the research I've done, I think I'll need a pump that can put out about 2,000 gallons per hour with a head of about 6 to 8 feet.

Does this sound like it will work? Is that pump sound about the right size? Any comments on making sure this will not fall over?

Thanks in advance for your advice.

opnorty

 

[sissy]

oh my granite heart .Remember the longer the hose from the pump the less gph you will have and going up less.

 

[sissy]

Another comment remember broken granite is very sharp on the edges almost like glass and any one rubbing or leaning against it is at risk .You may want to get a grinder and grind off sharp edges .I know about the sharp edges first hand and have the scar to show for it .

 

[addy1]

Make sure you seal between each piece of granite really good so the water does not seep back and out of the pond. Or you need a piece of liner under the granite to keep the water going into the pond.

If you stack them well and silicone together, they should stay up.

Agree with sissy, it will have sharp edges.

 

[sissy]

will silicon stick if the granite is glossy

 

[addy1]

It would need to be tested, ie stick some together and see how it does. I have put up glass with silicone and it has stuck well, but roughing it up would really help. Quick jap with a grinder, heavy sand paper give it something to grip to.

 

[opnorty]

Wow, thanks for the quick responses.
As usual, I forgot a couple things in my original post. I am planning to put in a rubber liner for the receiving pond at the bottom since it will be full except when emptied for the winter. I am thinking about slightly tipping the slabs out so any water that gets between the granite will run out to the face of the waterfall.

I have found out first hand how sharp the broken granite edges are. I sliced open the top of my knuckle and ended up with stitches. Also, granite is really heavy. A piece I was breaking dropped a piece on my foot and left a pretty good mark/bruise. This could get really painful by the time it is done.

opnorty

 

[addy1]

lol glad it was not worse. Make sure of your tilt, water has a way of going where you do not want it to go.

 

[Waterbug]

Staining
Granite will be attached directly to the retaining wall? If yes I'd guess you'd lose a lot of water. Concrete absorbs water. I assume you'd start to see a dampness on the wall "outside" of the granite, and beneath the surface the dampness will extend much further. Because water will evaporate at the surface you will probably see staining and discoloration form over time. Even when the water feature is removed a very strange stain will remain forever. That could really hurt your home's value.

Silicone and Goop
Virtually every first time DIYer chooses silicone or some other quick and easy sounding glue rather than cement mortar which is what professionals use. I'm guessing it would take about $200 worth of silicone or $30 worth of mortar. Cost however is not the reason professionals use mortar.

When you go to glue the first piece you will notice two things. First how long it takes silicone to set. Second gravity. You'll have to figure out a way to brace each piece for the 24 hours it takes silicone to set, and that's not the cure time. Gluing say 1/2 ton of rock to a vertical surface...can I watch? You could instead use epoxy, the second most reached for glue by first time DIYers...until they see the cost. That normally stops them from having to experience mixing about a million little batches or trying to clean epoxy from, well, everything. And even epoxy has a long set time when you're talking about holding a thousand pieces in place for 3-5 minutes each.

Set time still isn't the primary reason professionals use mortar. It's life span. Mortar can last hundreds of years. Silicone will last many years...but its bond to the concrete won't last. Water and bacteria will get between the silicone and concrete, perfect home for bacteria, and over time the acid from the bacteria will break down the thinnest (like a single atom) of the concrete and that is all the silicone was bond too. Same for the metal brick ties. Mortar products on the other hand weld to the concrete almost becoming a single material.

First time DIYers are often fearful of mortar thinking it takes great skill. It doesn't for these types of applications. If you were building a block wall and you wanted all the joints to be straight then sure, great skill is needed. For gluing rock...almost no skill is needed. Think of it as mud.

BTW I used silicone when I was a first time DIYer and was afraid of using mortar too.

Weir
For the weir you might consider a PVC or ABS pipe with a slot cut lengthwise with a plunge cut on a table saw if you can find someone with a table saw. Get a long weir to work isn't easy and the pipe is the easiest to tweak imo. A gutter just isn't rigid enough imo. Or holes in the gutter...still difficult but you can adjust flow by drilling more holes and plugging others.

Shedding Water
Tipping stone downward does sound like they would shed water...but surface tension has something to say. Water will run back on the underside unless the pitch is a lot.

Big, first time, project...maybe a test is a good idea...
You might try making a small waterfall out of the granite first to see if you like the look. I once used granite tile the same way, broken up, stacked flat. I personally didn't care for the look. The flat sides were still visible and the uniform thickness looked man made. That's just my taste, might be cool for your taste. However I do think the granite could be really great when used in a modern design style rather than as a natural element.

Another test you can do is buy a tube of silicone and run a bead on the concrete wall. Wait a week, a month, or whatever it takes for it to cure, and then pull it off. Most likely you will say "Wow, that came off easy".

 

[Fishylove]

Wow, thanks for the quick responses.
As usual, I forgot a couple things in my original post. I am planning to put in a rubber liner for the receiving pond at the bottom since it will be full except when emptied for the winter. I am thinking about slightly tipping the slabs out so any water that gets between the granite will run out to the face of the waterfall.

I have found out first hand how sharp the broken granite edges are. I sliced open the top of my knuckle and ended up with stitches. Also, granite is really heavy. A piece I was breaking dropped a piece on my foot and left a pretty good mark/bruise. This could get really painful by the time it is done.

opnorty

Oh it gets better, got lots of flint stones from the coal pits, stepped on one in the dark and cut my foot open stupid rocks!

Opnorty be sure to use marine grade silicone, and as far as the shiny surface, I believe if you would ruff it up where you were going to silicone it should stick.
Oh, And welcome

 

[sissy]

I thought about mortar but wondered about it's sticking power on granite with the force of water .I know most granite comes with a finished side and an unfinished side so could work just wondered over time being outside with the freeze and thaw and moisture if it would crack or break off the wall .I have never used granite outside but guessing it would be no different than stone or fake stone or brick .Thats a lot of wall to cover and why would you have to empty in the winter .Will a liner really hold up to that .

 

[brokensword]

I'd use mason cement, not mortar, as the former is waterproof and the latter is not. Just my two cents from having a bricklayer as a father. And there's a reason brick ties are used when doing a vertical wall. Might try and make this self-standing and not depend on anything behind your waterfall wall. Just sayin'

btw, IF you were to use cement though, it's a b*itch to break loose in the future, whereas mortar is designed to be the weak link re brick and bond. IOW, would be hard to re-use and tear-apart, a cemented granite wall. But would be waterproof joints and a lot stronger.

Michael

 

[opnorty]

Thanks again for all the suggestions. I have given up on the idea of using silicone. Thatwas a suggestion from my friend where I am getting the granite. He said that is what they use to hold down the countertops. After thinking about that a little bit, I decided that I didnt trust it to hold up to the weight. Im not afraid of mortar. I am a civil engineer during the day and a former flooring installer. Mixing it up and troweling it on the stones is not a problem for me. I am also goindg to do a litle test area to see how it goes. The brick ties were a suggestion from a structural engineer friend of mine. I think the should help keep the wal from tipping out from the concrete wall.

Thanks again. Keep the suggestions coming.

 

[Waterbug]

I'd use mason cement, not mortar, as the former is waterproof and the latter is not.

Mortar is a general term for many, many products and recipes. I've never heard specifically of "mason cement" and Google didn't turn up anything, so I don't know what that is. Are you talking about type 0 or N vs type S or M mortar? None of these are waterproof so I'm not sure what's being referred to.

btw, IF you were to use cement though, it's a b*itch to break loose in the future, whereas mortar is designed to be the weak link re brick and bond. IOW, would be hard to re-use and tear-apart, a cemented granite wall. But would be waterproof joints and a lot stronger.

I've often heard people want the "strongest" mortar. They're generally talking about compression strength. The more Portland cement (and some other factors) added the greater the compression strength. It seems like "compression" gets dropped.

Glass has high compression strength, but drop a glass bottle and you see that compression strength isn't the same thing as "strong". The same with mortar. As any good bricklayer will tell you a high compression strength mortar is a poor choice for clay bricks. The mortar stays rigid while the bricks and building moves and the whole thing falls apart faster. Some (OK, a tiny number) bricklayers are even going back to line mortar (no cement) because they feel it lasts longer if properly maintained.

Personally I would stay with type N, maybe type S, or something in between. Or maybe even a Thin Set mortar. Lots of choices.

 

[Waterbug]

I am a civil engineer during the day and a former flooring installer. Mixing it up and troweling it on the stones is not a problem for me.

I see, very good.

The brick ties were a suggestion from a structural engineer friend of mine. I think the should help keep the wal from tipping out from the concrete wall.

I would check this again, or maybe I don't understand the project. I've been assuming you're attaching the stone directly to the concrete wall. If that is the case there's no reason for the ties.

A brick veneer, like a house, is basically a free standing wall up against a bearing wall whether made of wood or concrete. The bricks are not stuck to the bearing wall. Instead there's a gap between the bearing wall and the brick. So in this case the ties are used to keep the brick veneer from falling into or away from the bearing wall.

In your application each stone is bonded to the concrete. Much more like laying tile except your material is thicker. I'm not sure how far out from the wall the stone will protrude, I assume less than 4"? That should be fine.

If the stone sticks out 6-8" I still don't think you'd need ties, but a foundation for the veneer would start to be more important. Think of it this way, if you do use ties to keep the stone from falling away from the wall then that means the stone is not attached to the wall very well. If that's true then what's supporting the stone vertically? What I'm saying is if ties are needed then so is a foundation. If ties aren't needed then neither is a foundation for the veneer.

Attaching ties to the concrete wall doesn't sound like fun.