The option for selecting whether to use a mortared flagstone or a dry set
flagstone should be based on climate conditions. If you live in an area
which experiences considerable winter frost heave, the stones should be
mortared in place. If this is not the primary concern but there is the
potential from root disturbance, then go with the dry set - it is easier
to left and resettle. If the base is prepared correctly for either method
and the stones are properly laid and seated, there should be no
irregularities or unevenness in the surface of either method.

I live in an area where frost heaving is not a concern, but where tree
roots are a recurring issue. Nearly all of the patios and terraces I
specify in my designs have been laid using the dry set method. There have
never been any problems with settling or unevenness, except when roots
enter the picture. The stones can then be removed, adjustments made to
accommodate the roots and then re-laid. Very simple process.

pam - gardengal


kellysheroes wrote:

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?