lindagreg Wow! Thank you very much for your input! Will check out those helpful links...we r being told to put some mortar under each stone to help level as each piece is different. We put fill sand as a base already and it is little aggregates with some sand mixed in...

Integration Design Studio, Landscape Architects The sand with some little aggregate should be fine. Based on our experience the mortar under the stones is not needed if you are talking about larger pieces of flagstone (24" and bigger). Most masonry contractors will use the sand as a leveling base, and either add or subtract some sand under each stone so that the final product is level.