Durability of stone over concrete?

Question

My concrete sidewalks are an inch or so below grade (presumably sunken since installation by previous owners?) and are beginning to crack. I'd like to install flagstone pathways in their place. It looks like, in general, laying stone over existing concrete is acceptable. It also looks like I can use 1/2" of sand and 1" thick stone to get the walkaway about 1/2" above grade which seems suitable.

In addition to aesthetics, I'm interested in replacing the walkway with stone for long term durability. Will the pathway be as durable laid over existing concrete as it would be if I demolished the concrete and installed it more conventionally?

Answer 1

About durability: it is difficult to tell. Concrete is a artificial rock/stone, not so far from flagstone.

There are a lot different type of stones, some cracks more often then other (also between flagstone). Also the size matter. I seen thin layer stone used for pavement (because they are cheap), but so they crack quickly. Also too large stones tend to crack more easily if the base in uneven (underground water!).

As far i remember, flagstone are not the more hard and resistant stones.

But the main problem is the "sunken". This is independent of material. Or it was not placed as one should ("foundations"), or the soil is not even (maybe because of changing water in soil (differences between dry and wet weather)). I would check this, and maybe I would do a oversize pavement, so that I would not park/go on the same spots every time. If actual concrete is still sinking, I think there is no advantage to keep it as foundation.