What would you recommend as the best option to bond flagstone to an outdoor concrete patio in the Kansas City area?
I have seen two successful approaches, the first was to dry lay the paving stone in a fine damp sand bed. Butt the edges tight and sweep in a fine sand to fill the butted joints. This process gives you total control over design pattern and of course, any easy way to change the pattern or lay out of the paving stones.
The second way, mix a mortar bed of mortar sand and cement and water. The paving stones have been through a "rehearsal" for the pattern layout. Place the mortar bed about two inches thick, press in each paver and let it seat about one half of it's thickness into the mortar bed. Do not squeeze the mortar up and in between the paver joints, so as to well all the way out of the joint. Just seat it, do not bury the paver. Continue on with the paver lay out until complete. Come back in a few days and grout in the joints with a similar mortar or try for a contrast with a different color.
You can grout the paver joints full and then trim the excess even with the top of the paver stone. Wipe the mortar slurry off and rewipe the area until it is free of mortar stain. You can choose to seal your paver stones with Lumiseal Plus, it will give them a shine and a seal at the same time.