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

[dadiOH]

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?

[dadiOH]

Just a technical FYI, quartzite is not granite; it is metamorphized sandstone. For that matter, what most people call granite isn't granite; "igneous rock" would be a better term.

[dadiOH]

If you want the outside edge of the stones to be flush with the outside vertical wall, you would be hard put to cut them after laying without screwing up the wall.

If I were doing it and wanted that edge to be straight, I would...

1. Dry lay the stones. Note that the inside edge need not be chock-a-block to the pond wall (IMO)
2. Draw a line on the underneath front edge of the stone, number the stones sequentially on the top.

2a. If you think you'd have trouble getting the stones back where they belong, mark the edges of the stones on the vertical walls.

1. Cut all the stones on the line you marked
2. Lay the stones aligning the front (outside) edge with the wall.

[Jim Elbrecht]

-snip-

There may be a special one of these for stone-- I know they are indispensable [to me] when setting heavy blocks or carry bricks-

Jim

[Chuck Banshee]

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.

[dpb]

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.

[Chuck Banshee]

I'm confused.

I thank you for the description - but I don't understand as you 'seem' to be talking about cutting the edge near the wall. Please allow me to clarify (in case I explained it wrong).

The edge near the vertical wall is already cut. So are the side-to-side edges (next to each block).

The edge I'm unsure about is the edge that eventually ends up in the grass. That's what I'm calling the outside edge.

Here's a picture, taken just now at first light, that has the edge that I was asking about pointed to.

I am not sure if it's best to cut that pencil line (which cuts the length of each stone to exactly fifteen 1/2 inches away from the wall) BEFORE or AFTER I set the stones in cement & mortar???

(Note: Unless suggested otherwise, I plan on cutting that line AFTER I lay the stones permanently. That way, the outside (cut) line will always be straight. I plan on snapping a chalk line where the pencil marks now are and then slicing it with the circular saw & diamond blade.)

But I've never done this ... so that's why I ask. It just seems too hard to get that outside edge straight any other way.

[dadiOH]

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.

[Chuck Banshee]

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.

[gfretwell]

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.

[Chuck Banshee]

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.

[gfretwell]

All I know is that it is as hard as Chinese algebra.

[Chuck Banshee]

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!

[gfretwell]

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.

[Chuck Banshee]

It was my fault for confusing all the terms (cement, mortar, concrete, etc.).

This half of the flagstone walkway already has an old 'concrete' base (which I found unexpectedly when I dug up the lawn). So, all I will be doing is putting 'mortar' on top of the concrete, about an inch (or so) thick.

Then I will lay the flagstones in that bed of mortar and I will fill the half-inch in between each stone with that same mortar.

Since the flagstones are of varying thicknesses, I will tap them with a rubber mallet and use a level to level them off.

Then, after it all sets (a day or two later), my plan is to snap a chalk line and then saw off the outside edge as shown in the previous picture:

The reason for sawing AFTER (and not before) is that I am hoping to get a straighter edge than if I tried to even up each and every flagstone while I am setting them in mortar.

Is this plan 'normal' to saw the ends off last?

[Chuck Banshee]

That's a good point. I've already ruined a couple by chipping as I was cutting them.

Of course, that then means I have to be extra specially careful that I put the mortar in the "grout slots" (whatever the slots between stones is called) perfectly at the outside edge - or there will be messy blobs.

Hopefully, when it's done, I'll snap a picture and you guys might approve (with caveats, I'm sure). :)

[dadiOH]

The slots are called "joints". Or even "spaces". You pack the grout into the joints and yes, it will ooze out at the outside edge. After it sets a bit - or even before depending on how stiff it is - take a trowel and cut off the ooze out. Later, improve it more with the grout sponge someone mentioned.

[Chuck Banshee]

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.

[dadiOH]

The concrete was under the lawn? Be SURE to clean it well before you lay anything. I hesitate to mention it but hydrochloric acid (muriatic acid) works well for that. A dilute solution...and note that one adds acid to the water, NEVER the reverse.

[Chuck Banshee]

Yes. So were the sprinkler heads.

This picture has an arrow where the concrete is now - and where the soil line was before I dug it all out.

Hmmm... I can get hydrochloric acid but why would it need cleaning with acid if it's just dirt?