Question
I very much appreciate your response, but if I am in a desert climate with no chance of freezing then is a concrete slab required? Or is a very well compacted base sufficient and then mortar the gaps? I do appreciate your help.
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Followup To

Question -
I recently purchased 500 concrete faux flagstone pavers from an individual, these are irregular shaped "flagstone' look alike in 2 inch thickness varying in sizees of 16x15 inch. I plan to build a patio around my existing pool deck. I live in Arizona and am curious as to a "wet" or "dry" base to get going.

Being in the desert climate can I set them on a sand base and then grout between or should i set on a mortar base?
Any help would be appreciated.

Answer -
The real question is do you want this to last and look good for a long time?

If the answer is yes then you should pour a concrete slab first and mortar the parvers or stone down to it then grout(mortar) between the joints just like laying tile. This is the best way.

If you set pavers on anything other than a solid slab it is what we call in the industry "a flexible base". Crushed and compacted granite fines, gravel, sand, etc. all fall into this category. When the ground freezes these bases move just a tiny bit but it is enought to cause surface treatment to heave. So if you mortar between the joints it will eventually be broken up by movement in the ground. These types of installtions usually do no tlook good several years down the road.

So if you dont want a slab and broken grout joints the best thing to do is to put down a "sub-base" of about 3"to4" of crushed gravel and compact it with a small plate compactor (you can rent this), steel hand tamper (local hardware or masonry supply store) or make yourself a hand tamp with a 2x4 and a 12x12 3/4" sheet of plywood nailed to one end.
Once the sub-base is well compacted apply a 1" sand setting bed using a 2x4 to screed it across the compacted sub-base.  Make sure the sub-base is level first with a 4' level as your screed. Also keep the sand level. Use only mason's sand witch is fractured not round wind blown sand Mason's sand compatcs much better and locks in place.

Once this is all in place you may place the pavers across it leaving small gaps as you desire beteen each paver.  Lightly tamp each paver with a rubber mallet and a piece of wood about 12x12 so that you are spreading the force of the mallet across the entire paver.

Once all the pavers are in place you will want to fill the gaps with something. This is up to your preference. If this patio is near a heavily used entrance to your home you will want a small gravel that will not stick to your feat and get tracked in the house. I use something called 'Permatill' that is no bigger than a pea. You may find this locally by googling it for a supplier in your areas. Otherwise you should look for "expaned shale" or a very small gravel.
If the patio is a long way you can use more sand.
If you want plants between each paver then fill the gaps with applicable garden soil for your area and top it with small gravel.
I would not apply mortar in the joints unless you also mix some portland cement into the sand setting bed and your area is free from frost or ground freeze.

Answer
I personally would never mortar between stones or pavers that are on a "flexible base". Even if your particular climate does not freeze, just you walking on the pavers over time will cause them to compact or move and the mortar will crack or break loose. However, thats just me and I am a perfectionist... a lot of perople do it anyway and its fine for a few years...but eventually it will start to break up and look bad, trust me on that. Again, if you are set on mortaring the joints then add portland cement and a little water to the base and sub base so that it sets up and is no longer flexible. Typically one shovel full of portland to 3 shovels of crushed aggregate or sand is about right. Make sure it is mixed together well. After you set the pavers but before you add the mortar in the joints wet the hole area lightly for a few days. Let it set up for a week before adding mortar.