# Applying flagstone to cinder blocks



## poet2dager (Aug 16, 2010)

I am building an above ground pond, I bought flagstone hoping to place it on the wall of the pond to make it look more natural. I am trying to find a good material to use to get the flagstone to stick to the wall, all the larger pieces will be flush with the ground so what I use doesn't need to support a large amount of weight. I have heard an idea on thin-set, stuff for laying granite and marble, but I wanted to get some more opinions. I am new to most of this stuff, but if someone could point me in the right direction, it would be greatly appreciated.

thanks!


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## CraigFL (Aug 16, 2010)

You say "flagstone" but we need to know if is man-made for veneering or actual/natural flagstone. Veneer stone would be lighter and easier to apply. Also, what kind of surface is the pond?


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## poet2dager (Aug 16, 2010)

It is natural flag stone, and most of the pieces are 1 1/2 inches thick, as far as the surface of the pond, it has a small small concrete layer with cinder blocks going around it as a wall, this wont be an in ground pond. the cinder blocks have mortar on them to connect them to each other. I have gotten this far but am not sure what would be the best way to finish it. I just need to put the liner in and attach the flag stone to the cinder block wall, it is only one cinder block in height.


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## itsreallyconc (Aug 17, 2010)

fit the flag onto the exposed part of the conc base & slap 'em on w/mortar,,, just be certain the block's CLEAN 1st.


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## oldognewtrick (Aug 17, 2010)

I am curious as to how you are going to water proof the walls. Are you going to use a liner or try and seal the block somehow?


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## itsreallyconc (Aug 17, 2010)

maybe i miss'd something,,, ' just need to put the liner in and attach the flag '


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## poet2dager (Aug 17, 2010)

yes, I am using a pond liner, cinder blocks are just to add support and some height so the water won't be too shallow and heat up the pond during our hot afternoons. 

Itsreallyconc: my first plan was to clean the blocks get some mortar and like you said, slap them on after fitting them, but I wasn't sure if the mortar would be sticky enough to hold up the blocks until it dries.


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## itsreallyconc (Aug 17, 2010)

if i'm reading your op correctly, there's a bit of the conc footer showing,,, the mortar will hold the vertical pcs of flag but not suspend them as it would act if you were to face a home for instance.

we'd use a mortar bag to fill the jnts 'tween the flag then ' tool ' the jnt as you would w/any brick/stone/mortar work.


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## poet2dager (Aug 17, 2010)

I am probably at the lowest level of knowledge about masonry, would you mind explaining what ( 'tool' the joint) means? or maybe direct me to a website that could help?


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## itsreallyconc (Aug 17, 2010)

hie thyself over to an apro0n store & buy a book on stone/brick work,,, you should see a picture & description of joint ' tooling ',,, probably easier finding it there than the library.


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## poet2dager (Aug 17, 2010)

Any suggestions on what kind of mortar I should use? something strong that will give a little for expansion and contraction? I also need something that will stick well to the cinder blocks and keep the flagstone upright. Thanks for all your help!


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## Msupsic (Aug 18, 2010)

I took some classes on ponds and gardens a few years ago. The guy who taught the course used to do in-ground ponds with cinder block all the time. He would dig the trench, and then line it with the block. He would then place the liner in the lined hole, and set the flags on top of the blocks and liner, loose, and just let the weight hold things in place. Of course, the weight of the water also held things in place once he filled the pond.

Since your pond is above-ground... I'm assuming you are going to mortar or somehow anchor all of the cinder block so that the structure holds its shape? Otherwise, you run the risk of the blocks moving or shifting and then your stone facing will just crack and fall off. Especially since the pressure of that water will be pushing outward with some major force.

Yes, you can stick the flags to the cinder block with basic masonry mortar. There are some additives, latex, etc. that you can add to the mortar to make it more, "flexible". But if your basic structure is solid, you won't have to worry about that.

You can also use a heavy duty construction mastic (glue), which comes in a caulking tube and is like iron when it dries. Just be sure to apply a nice, thick bead of mastic under each stone. You should be able to take your hands off of each flag as you stick it on; the mastic should be thick enough that the stone stays in place.

The person above is referring to "tooling" the joints. Buy a bag of regular masonry mortar at your local home repair store. Get a joint "bag," which is like an oversized canvas pastry bag. They should sell them in the same area at the store. Mix your mortar with enough water that it can be squeezed (like cake icing) out of the end of the joint bag. Don't make it too runny, it will be a mess and won't dry strong.

Squeeze the mortar into the spaces between the stones (the joints), using enough to get under the joints and behind each stone. In other words, fill the cracks up until the mortar bulges slightly above the level of the flagstone.

Then take a trowel, or a joint tool (which is basically a piece of metal that looks like a butter knife in the shape of a "v"), and smooth out the joints so they look pretty. As the mortar dries, use a wet rag to wipe any extra mess off of the flagstones themselves.

Sounds complicated, but it's pretty easy. Almost anyone can do it. You just need lots of patience.


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## poet2dager (Aug 20, 2010)

thank you for your help, I already tooled the joints when I layed the cinder blocks, my last few steps are putting the liner in, cutting away the excess, and attaching the flagstone to the cinder blocks. I want to make sure to get all the sharp rocks out of the pond so the liner won't get punctured. I will try using mortar on one and construction mastic on another to see what works best, thank you for all your help and your explanation, I really appreciate it.


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## Msupsic (Aug 20, 2010)

No problem, glad to help.

I was referring to tooling the other joints, the ones between the flagstones after you stick them to the outside of the cinder blocks. You plan on leaving a small gap between each flag, too right? Then you need to fill and tool those joints too.

Best of luck!


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