The problem with not removing the sidewalk is that you need drainage. If there is a heavy rain, the sidewalk can "hold in" the water, and cause the sand to become "soupy". Then any steps on the stones will squish the sand and cause the stones to be uneven.

If your sidewalk has a big slope to it, you may be alright.

Sand is for setting the stones, and should be 2 inches. Do not use 3-5 inches, that leaves too much room for shifting. Use 3 inches of gravel, tamp it down, then 2 inches of sand over that.

Overall, ensure that heavy rain has someplace to drain to, to not pool in the sand.

How large is the new patio (1)sidewalk area and (2) grass area? Also what is on the other side of the purple line - more sidewalk?

Thanks for the responses!

gottagarden - the sidewalk actually does have some slope to it. It slopes down toward the left of the picture. In fact, my entire yard has a pretty decent slope moving from right to left in the photo. For example, that corner that you're seeing in the picture is the NW corner of my house. In the crawl space on that end of the house, I have to almost literally crawl on my belly, but in the crawl space on the opposite end of the house, I can almost stand up.

Hey bailey09 - the sidewalk area is maybe about 30-40 sqare feet (approx. 10' x 3'), and then the grassy area will cover say another 30-40 sqaure feet.

On the other side of the purple line is where wood steps lead up to the "upper level" of my wood deck. The sidewalk continues under the steps for a few more feet, and then "drops off" to a large concrete slab that the largest part of my deck covers. As I said above, the whole area has a pretty steep grade moving from right to left, so the whole area drains pretty well.

Here's another image to illustrate - if you look in the lower left corner of the picture (through the railing) you can see the steps leading down to the sidewalk:

{{gwi:288136}}

Jeff, I guess I was asking about the blue line. It looks like the sidewalk continues down the side of the house. Wouldn't it be awkward to have to step up to get in the back yard?

The sidewalk looks in good condition so I would not take it out. I would mortar the flagstone to the top of the concrete sidewalk and then either (1)pour a 2"-3" concrete base (like a footer) in the grassy area and then lay the flagstone on top, or (2) use a 2"-3" crushed granite base and sand to level with a sprinkling of cement to hold the flagstone in place, or (3) as a last resort lay the flagstone in the grassy area and remove the grass from beneath the stone, use sand to level. I hope my options make sense.

bailey

Hey bailey --

Yes that sidewalk continues down the side of the house, but it continues for about 10-15 feet before hitting a gate that goes into the front yard.

Practically nobody uses that gate and walkway except for me when doing yard work (virtually all guests enter our back yard through the house), and I'm not sure I understand what you mean by having to "step up into the back yard."

While the flagstone wouldn't be level with the concrete obviously, I figured it would only be raised up maybe 3-4 inches when all was said and done - considering that a 2" thick flagstone would be set into a 2-3 inch bed of sand.

Am I missing something?

That white retaining wall doesn't look to me as though it goes underground. If you want the sand retained underground, you need to install edging. There is plastic edging you can buy especially for this purpose, some that curves, some that goes straight. Can be bought anywhere you can buy paving stones, I'd think. It's L-shaped though; you might just use lawn edging.

I sympathize with not wanting to remove the concrete, but agree that mortaring on top of it would make more sense. In effect, you're not installing one patio here but two different ones that abut and adjoin, even if some of the stones go across the divide between them. Treat the base preparation differently.

Thanks again for all the reponses.

Quick question about mortoring the flagstone to the concrete:

This may be a dumb question, as I have no experience mortoring or laying concrete - but is it OK that the concrete sidewalk, as is, is not level?

As I said earlier, it has a bit of a grade to it, slanting down from right to left in the photo. Does that mean that I would just have a "deeper" layer of mortor on the left side and the flagstones would then be leveled as I lay them?

Also - for the part that would be mortored to the concrete - would I still be using sand "in between" the stones? Or would that also be mortor? I guess the reason I ask that is because it would seem to be the case on the part laid on the grassy area -- or have I confused myself? ;-)

I have never mortared onto concrete so don't know about thickness of mortar changing. I do know that you can get varying thicknesses of flagstone in a lot, and so you could use thicker pieces lower on the slope.

I also don't know about the sand, sorry. Try asking at the stoneyard.

Jeff, the level is up to you. You can level the area by increasing the amount of mortar or maintain the slope. After you have laid the thin flagstone on the concrete base, and it has dried, you will grout between the stones. Be sure to use some admix (like elmers glue) in your mortar mix so you get a good bond to the old concrete pavement.

On the grassy area: You are going to remove the grass down maybe 3" and add crushed stone or granite gravel, lower than the old sidewalk and depending on the thickness of your flagstone. Now tamp it down (again leveled or slopped)and sprinkle some dry portland cement on the top. In this area you want to use a thicker flagstone and you are only going to use enough sand to level the stone. When all the stone is down mist everything so that the portland grabs onto the flagstone and the gravel. Now you are ready to grout between the stones and it will look like one continuous patio.

The only place that you will need edging is where the stone is not held in by something e.g. the edge where the steps are. I've actually used the thin edging for pavers that you get at the big box stores.

My step comment had to do with the blue line and the lag bolt trim pcs but if you mortar the flagstone you won't need anything special there.

Bailey

Thanks again for your response Bailey - that makes perfect sense and it's the way I think I'll go.

One more follow-up - is there a good guidline on the amount of admix to add to the mortor? I have no reference point for that... are we talking one large bottle per wheelbarrow or something similar?

Yes that should work for what you are doing. Just be sure to first mix the admix (bonding agent) with 1/2 the water before you add it to the dry ingredients. Mix well and then add what you need of the remaining water. Remember, the less water in your mix the stronger the bond.

Bailey