You can do either, but a mortar inlay will be (well, should be) more costly
because the foundation must be very stable. This means digging deep and
removing soil, laying and compacting gravel and sand, then the flagstones.
With sand or crushed stone as your 'mortar', you don't need to dig as deeply
nor prepare the foundation as intensively.

Dave

"kellysheroes" wrote in message
m...
We're planning on having a 1000 ft2 flagstone patio installed. We
have received estimates for both a dry install with rock/stone(?) dust
and a mortored install. What are the pros and cons of each. We live
in Northern Virginia by Washington DC. We do have a large, mature
sugar maple that will be approximately 6 feet from one corner of the
patio. Our concerns are these roots and heave. We want a very flat
surface which leads us to mortored, but are afraid of cracking in the
cement due to the roots. We believe that we can repair any root
movement in a dry install, but worry about the overall flatness over a
period of time. Thoughts?