# What is UNDER flagstones on concrete? How do you keep the tops level? (Pictures)

This weekend I will finally start cutting & cementing the flagstone on the walkway (see four photos below for detail) and three questions arose:
Q1: What is UNDER these flagstones on cement (are they glued?) Q2: If you glue them, how do you keep the tops evenly flat? Q3: Since the step width varies by 3 inches, can it take a 3" overhang?
Here is a picture of the concrete base that I plan on putting flagstone. Notice the base starts at 18 inches but eventually narrows to 15". Can a 3" overhang (maximum) be supported with just the packed soil below?

Here is a picture of that same base, only further away to give you a better idea of the problem set:

Here is a picture of the enigma. What is UNDER these existing flagstones? Are they simply GLUED on? (There seems to be NOTHING under them!)

Here is another picture of the existing flagstones in the water feature. They appear to have NOTHING under them. Can that be?

The reason these three question matter is: a) I need to lay the flagstone on the concrete and I don't know if I glue them on or if I just grout the spaces between each stone. b) If I glue them on, I don't know how to keep the tops flat since each stone is slightly different in thickness. c) Even though the base starts at 18" wide, it narrows to 15" wide but I would want the stone to stay the same width.
Any advice is always appreciated!
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On Sat, 28 Jan 2012 07:22:25 +0000, Chuck Banshee wrote:

Here is a view further out showing the entire construction zone:

The problem I'm having trouble figuring out how to solve is how to put flagstone along the foundation where the front side is in dirt (with water pipes unexpectedly popping out when I dug the path) - and the other side having a 15" to 18" concrete ledge to put the flagstones upon.
How would you suggest I lay the flagstones so that one can walk along the side of the foundation?
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On 1/28/2012 1:33 AM, Chuck Banshee wrote:

Chuck, you have more loam to remove. Get a healthy load of "red select" or whatever compactible select fill is normally available in your area. Set up an edge form on the outboard edge of the proposed walk. It will work to grade to a chalk line at the foundation, but it will be easier to set a grade screed there also. Install, grade, and compact the fill. You have no requirement to follow the paint line that is established on your foundation, the walk can follow the layout of the top cap of the foundation wall which will allow you to go over the pipes with the fill, raise the control box to the stone grade, and have your stone walkway. If you ever need to work on the pipes, everything is fairly easy to remove.
--

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Keep the whole world singing . . .
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On Sat, 28 Jan 2012 00:27:40 -0800, harry wrote:

For half the walkway, there is already a concrete (rough surface) foundation. That's the half I'm doing first (because it's easier).
Here is a picture of the step up I tried as the very first effort. http://picturepush.com/host.php?imaget48448
It took 1 bag of mortar (50#) and one gallon of water. No sand. No rocks.
In hindsight, it wasn't enough to raise the level the required two inches ... so I have to start over again today.
I did cut the rocks to fit almost seamlessly. The cutting is the easy part. The hard part is figuring out how to glue it all together.
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On Sun, 29 Jan 2012 21:12:22 +0000, Chuck Banshee wrote:

I think I used the wrong stuff.
What I used was pure mortar (no rock, no sand).
The entire bag barely brought this small spot up to the level of a single two-by-four set flat on the ground!

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No you have to realize that when you are laying a mortar bed to raise something up you have to let it set and it does take quite a bit of material to fill what you think looks like a small volume of space...
When you have a flat, leveled area that is close in elevation to where you want your finished flagstone whatever to be at you would then use a shallow bedding coat of mortar to lay the stones in... If you set the pavers on the wet 2" of mortar they would sink unevenly into the wet mortar depending on how heavy they were and the mortar bed would take forever to cure...
~~ Evan
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On 1/29/2012 4:34 PM, Evan wrote:

Why would it take longer for the mortar to cure?
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Chuck Banshee wrote:

There is no such thing as mortar without sand. Mortar is cement, sand and some lime. Add aggregate and it becomes concrete.
--

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On Sun, 29 Jan 2012 16:57:08 -0500, dadiOH wrote:

I appreciably stand corrected (I didn't ADD any more sand). :)
BTW, I've learned a bunch of 'little' things: * * * * * *
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On Sun, 29 Jan 2012 16:57:08 -0500, dadiOH wrote:

I appreciably stand corrected (I didn't ADD any more sand). :) I've never mixed cement/mortar before so this is a first for me. Tomorrow I hope to finish the job so I'll go to Home Depot to pick up about ten bags of mortar, concrete, sand, and rock.
BTW, I've learned a bunch of 'little' things so far: * Flip the ROUGH side down & the GOOD side up on all stones FIRST * Then SORT the stones by large, medium, & small (I put them on shelves) * Then SORT AGAIN, this time by square, rectangular, & triangular * Once they're sorted, lay the stones on the walkway as best you can * It helps greatly to put a thin board against the wall to give yourself room to judge where to cut the top line (against the wall) * Where funny shapes arise, it helps to put an entire stone on top of them * It helps to have something soft (like a towel) to pad your head as you're ALWAYS LEANING OVER with both hands on the stone so your head is the third leg of the tripod (your knees being the other two legs) * It helps to put a one-inch board between the cuts of the stone to get an idea of the finished fit * At some points, I just said TO HECK WITH IT and started cutting - at least putting a definite edge on a stone eliminated one variable - things went easier when I did that! * It takes a TON MORE MORTAR than you think it will! * Cutting the sandstone is very easy with a 7" circular saw with a diamond blade. The composite blade didn't work as well. * However, it's nearly impossible to REMOVE the blade! A normal wood saw has teeth you can jam a stick of wood in to immobilize the shaft. How DO you guys immobilize the shaft when using these composite blades?
PS: The mud had a benefit of showing exactly where the bobcat visited my construction site last night!

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Chuck Banshee wrote:

If you are buying concrete, why do you want sand and rock? If you are buying bags of *cement* you would need the sand and rock but you'd be far better off economically buying it by the yard from a purveyor of same. _____________

It should not take all that much to lay stone on an existing slab. All you need is about 1/2" + enough to keep the thinnest stone level with the thickest. If the stone bottom is highly irregular, butter it flat with mortar.

I use my fingers. Occasionally but rarely, visegrips. The shaft on your saw is shaped, right? The masonry blade hole is also shaped, right?
--

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On Mon, 30 Jan 2012 06:58:18 -0500, dadiOH wrote:

I'm not sure if I'm using the words right.
I'm buying 'stuff' to put UNDER the flagstones and 'mortar' to put in the joints above.
I guess that's 'cement' but I'll look up what 'concrete' is (because I thought they were one and the same). Mea culpa.
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On 1/30/2012 8:54 AM, Chuck Banshee wrote: ...

No, 'cement' is only the glue portion. Concrete is a mixture of mostly aggregrates (sand and gravel/rock, etc.) bound w/ the cement.
Mortar is a specific blend of cement and sand w/ additional addends specifically for use in stone/brick/block laying between joints.
--

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On Mon, 30 Jan 2012 09:09:07 -0600, dpb wrote:

I'm only just realizing I didn't have a clue what to call these 'things'.
I'll open up a separate thread to clarify the terms (concrete, cement, mortar, & grout) which I now know about only because I had to buy them just now at Home Depot.
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Chuck Banshee wrote:

I'm getting rather confused here. You are laying the stone on an existing concrete slab, right? You want something to hold it to the slab, right? That something is mortar. Could be Type N mortar...could be Type S mortar...could be thinset but they are all "mortar". When you put mortar in joints, it is called "grout". (For tile with very narrow joints, the grout is just cement, see below).

Cement is burned limestone. It winds up as a grey powder. Mix it with water and there is a chemical reaction that makes the powder hard again. Not very strong, though. Mix sand with cement (along with some lime) and you have mortar. Still not all that strong. Mix in aggregate - various sized crushed rock - and it is concrete. Strong as you can get with cement.
For what you are doing, you have absolutely no need for cement unless you plan to use it to make your own mortar and/or concrete. I doubt you are and if you are, I suggest you don't.
--

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On Mon, 30 Jan 2012 13:28:42 -0500, dadiOH wrote:

I've been using terms all wrong!
So the confusion started with me!
Today, I went to Home Depot to buy 'stuff', which turned out to be a choice between (cement + lime + aggregate) or concrete mix or mortar mix or grout mix (which is three times as expensive as mortar mix so I suspect something is different).
Anyway, I'll open a separate thread after I write this to clarify for me (and anyone else who cares to learn) to learn from you guys the differences.
I'm sorry for the confusion. It's my fault for being ignorant of the terms!
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wrote:

In this case he wants to use Type S, Type N is too soft.
I would only use the concrete if this was filling an inch and a half or more. We figured out setting the stone and filling the gaps in one step worked the best. Lay down a thing mud bed, stet the stone and press them to your final level, adding or removing mud until you get the whole matrix flat. Use the trowel to remove excess but don't wipe them yet. Let them set up a while before you do that.
Once you get a feel for it you can wipe them while setting but that is a trick that takes some learning curve. Too much water at this step will screw up the joints. It is still not the final wipe.
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On Mon, 30 Jan 2012 06:58:18 -0500, dadiOH wrote:

Today I bought what I needed.
Up until this moment, I've been mis-using the terms concrete & cement & mortar & grout.
I'll open a separate general-interest thread on what the differences are.
I'm amazed (and chagrined) that I've lived this long without knowing the difference between these 'things'.
So please take everything I've said with a grain of salt since I've been mis-using the terms by sheer ignorance.
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On Mon, 30 Jan 2012 09:24:26 +0000 (UTC), Chuck Banshee

The biggest mistake most new guys make is using too much water. You want the Type S mortar to be about the consistency of peanut butter, maybe even a little stiffer. Remember, you can always add water but you can't get it back out.
The hardest concrete is that which is barely wetted all the way through (less water comes out so it ends up denser). also If you get the mortar too wet, the stones will sink into the bed.
In your case, start from the top step and work down. Once you get your puzzle done, number the stones and put an arrow on them to indicate direction, lay then out on the step below in order, wet them with a hose, put down the mud bed on the step you are working on and transfer the stones into it. You may end up adding or removing the mud to get everything level. I would just do one step at a time since this is your first try. You will be wasting some mortar but mortar is cheap. Start with about half a bag and see how that goes. Don't go nuts cleaning the stone top yet. You just want to be sure you have all the voids out from under the stone and that they are in the right spot. (height/position). Once the mortar gets finger dent hard (maybe several hours if it is cool outside), then you can start wiping the excess mud off. Get a grout sponge or two, the big sponge with a rough surface on one side and a big bucket of water. You still want to be gentle on the stone and do not wipe out too much from the joints. If it is really cool outside that mortar may not really set hard overnight.
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On Mon, 30 Jan 2012 14:43:33 -0500, gfretwell wrote:

My first mortar mix was way way way too wet so I agree with you! (Although I used the 1 gallon to 50 pounds as stated on the mortar bag.)

Whew! I didn't see this until now but I bought 5 sixty-pound bags of "Sakrete Type S Masonry Mortar" ... so at least I got the right stuff.

Thanks. I'm going very slowly (about an hour per stone just for the cutting - so I suspect the mortaring will be just as slow - at least until I figure it out).

That's good to know. I picked up a big sponge to clean the tops of the stones. I'm not sure if I should use acid as I am unsure if it can damage the 'sandstone' flagstones.
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