Pavers Over Concrete --In The Dusty Desert
Here is a question regarding laying pavers over concrete where the area is very dusty.
We have a concrete patio slab and would like to put pavers on it. The slab is large, with expansion joints and each half tips towards the middle, where there is a long, one inch drain dumping water out to the edge of the patio. We have no problems with hard freezes and get only 7 in. of rain each year.
This is the question: if we use sand under the pavers, I'm concerned that washing off the pavers with a hose will cause us to lose the sand underneath it and the pavers will become 'rocky' to walk on. If we use thinset underneath, the pavers will be harder to hose off since the dirt will not slip between the pavers. This might not be a big deal except that this area is really, really, dusty. Thoughts?ANSWER
First of all, I assume you realize that you will have to address the trench drain that is in the middle of the existing concrete patio. The first thing that comes to mind is raising it to the new height. I am not sure what should be under it now as the new base. Also, The area where it empties the water off the patio will be higher, unless you add some fill and regrade.
If you are doing a lot of hosing off, probably setting the pavers on sand and also filling the joints with sand is not the best option. You might consider polymeric sand, which is applied and then wet down. After a very short while, it hardens.
I don't see a problem with mortaring the pavers over concrete for your existing concrete patio. When you hose off the pavers set this way, you should use a hard flow and force the water off the patio, not hose it so that it will go into the joints. There are many types of patios either of concrete or stone set in concrete. Once it is built correctly, hosing off is not a problem. This will be a much more stable hardscape for your situation.
The last option is to remove the concrete patio and start over with pavers, using polymeric sand. I would price it out both ways since setting pavers in concrete is more costly than using the dry laid method with polymeric sand. You also have the cost of digging up the drain and installing a new one. Just installing a new one is less expensive.