Having a stone patio installed is a big decision and one that requires a lot of forethought and planning. One of the choices that will have to be made is whether you should go with dry construction or wet construction.
Dry construction refers to stones that are not cemented together; the flagstones are rather laid on a bed of sand. One of the advantages of dry construction is that it is less expensive than wet. Besides the stone, all you need is sand and gravel. Dry construction has its advantages. For instance, many feel that it is more “forgiving” of mistakes. You may be able to make choices during construction or somewhere down the line you may decide to make some big changes, and it will be admitted that dry construction may allow that more easily.
There are drawbacks to dry construction however. The main problem is changes in the earthen foundation. If you live in a cold climate, season after season of freeze and thaw will definitely alter the earthen foundation. If you live in an area that gets a lot of soaking from the rain will also cause this problem. Dry construction is only recommended if you really are not worried about how the patio looks, and if you don’t mind doing periodic maintenance.
Wet construction refers to stone patios that are laid with a cement bed usually reinforced. Wet construction, since it involves cement is more complicated and therefore more costly. Also note that wet construction is more “permanent” then dry, which means that you will really have to know beforehand exactly what you want before building
All in all, dry construction is easier and better for the DIY man or woman about the house, but not reliable for long term patios. You might need to occasionally re-seat the stones, and make sure they are weeded in between. Wet construction is naturally somewhat more expensive, but it will give you a flagstone patio that is almost maintenance free. We prefer a 4 inch thick concrete foundation, and mortar the flagstone directly to the foundation. Nothing short of a sinkhole of an earthquake will affect it.