One thing I see on a fairly regular basis in this forum is someone showing up with a preconceived desire to proceed with a faulty scheme, or one that is only partially "baked." I can't tell yet if this is what is coming. Elbow, why do you want to lower the grade around the back door and create more of a step? (Usually, people desire less steps rather than more so it would be good to explain the reasoning behind the desire.) In lowering the grade, it will become important to know how the grade outside of the project area interfaces with that which is within. Of course, we can't see ANY of that and it has not been explained to us. This is not a question about water which gets into the joints between pieces of stone. It's about the much greater volume of water that doesn't get in and must run off. In the last picture, what you are showing is what most of us would call some sort of "flagstone" ... relatively flat, broad pieces of irregular shape. My own thoughts about this is that thin flagstone does not really make good paving when installed on a sand base (regardless of whether there is concrete under it, or not.) If you walk on packed beach sand, you'll notice that your feet leave an imprint because the pressure of your foot is enough to cause a shift of unprotected sand. While flagstone protects the sand layer SOME, it is THIN and CAN shift in small degrees (usually in a rocking motion) when pressure is applied and depending on the state of moisture content in the sand base. It can shift due to the action of freezing and thawing. Over time, these small shifts can add up to a cattywampus and not very pretty surface ... not the kind of thing you'd want, really, for a rock solid 100-year old barn and nice house. Thin flagstone makes a much better -- durable even -- paving surface if it is mortared directly on top of a concrete slab ... without any sand embedment layer at all. But this kind of installation, while not impossible as a DIY project, requires some learning and skill so is usually left to someone already with experience. Using this size project to "learn" on might be asking a bit much of one's self. It would be MUCH easier -- much, much easier -- to install a normal thickness (2 3/8" or greater) regular paving unit on an aggregate base: bricks, concrete pavers, uniformly cut stones, etc., if that's the type of base one wishes and if their experience is limited. One would still need to learn something, but it is much easier to develop skill for that than it is to develop skills at mortaring in flat work. You could use steel mesh in a concrete slab, but it would be pointless in paving laid on sand. I'm going to guess that the appeal of the flagstone is that you have access to it at a reasonable price ... but the other end of the equation is that its installation will be expensive (even if only in your labor the amount of time you must put in to learn, and the risk-factor of a potential botch.) As far as water that penetrates into the soil or below the paving ... consider that the soil is basically an ALWAYS DAMP medium. That's why the grade outside of a building cannot be raised to too high an elevation. If the grade is too high, the only solution is reducing it. Also, the grade around a building must be graded such that water runs away from the building (it is usually said for 10', but it depends to some degree on surrounding conditions.) If the grade elevation around the building is acceptable, then there is no reason to worry about the soil having some dampness. It's the way it is. What one should worry about is moving the excess rain water the heck away from the house ASAP. In the case of this paving, if you get the surface to drain properly, there is nothing to be concerned about with a little water entering between paving stones. The idea that you can put down a slightly subsurface waterproofing membrane to take care of water penetrating the soil is more likely to cause problems than solve them. It's not needed. And you wouldn't want to create a layer of water that has no real route of escape.

You know, it's interesting how when we travel to Europe or other parts of the world where we can see buildings several hundred years old, we appreciate the patina of age on things -- plaster showing its age, cracked stone paving, irregular color in brick, time-worn marble, and so on. In the US we always want to rip out the old, solid materials because of minor imperfectons, and replace them with something shiny, new, and not necessarily of equal quality. If there is a real problem with your tiles -- undermined and unstable surface, safety issues, water leaks, or whatever -- sure, replace them. But otherwise the older material has charm that pavers do not have, in particular with your nice brick wall and balusters. You'd want all your architectural elements to be speaking the same language.

Hi Cecilia Woods, HandyMac is absolutely correct about all the points he mentioned. It can be an issue because of the lack of ventilation under the deck as well as the concrete slab's ability to retain temperature. It can be a troublesome installation, but it can be done when the builder takes the appropriate precautions for the environment. There are other options like Deck Tiles that are squares designed to sit in a connector floating system right on top of concrete. No sleepers required, or any real problems as long as your slab is flat. Hope this helps you!

I think I'd rather deal with some cracking/sinking pavers now and then than to have to deal with potentially worse repercussions for doing the job "right." It seems to me the proper way to do a paver patio is only for certain property layouts and certain patio locations. My property was designed to direct rain runoff right past my back door, and the proposed paver patio would be in the flow's path. It's not going to get a lot of traffic... only light foot traffic, so I know that matters, too. I am wondering now, though, if excavation won't be a problem so long as I don't go lower than the excavated level of the existing concrete patio. That would give me at least a bit of depth to work with. Still, in the deep South, I have to wonder how much is truly necessary. It's not like it's going to heave with deep freezes every winter. [SHRUG] You bring up another concern I had, which was the sand washing out of the installation. I am not even sure how this isn't a given and something to be expected. I read that pavers can be installed on an existing concrete patio, something I was interested in doing to have the old and new areas match, but I was concerned because the recommendation was to put a layer of sand on the concrete patio. I immediately thought about the sand washing away over time.