Question
I am working with my cousin on a patio for his boss/owner of the company that he works for, we normally do brick pavers on the side so we shot him a price for that when we got to the job there were pallets of granite chip pavers for the border (not the problem) and giant thick slate slabs for the interior, he is going to pay for the difference but neither of us have dealt with such an extensive job, my question is how do we lay the slate we figured that the prep work was the same as pavers but we are nervous because none of the pieces are the same thickness and none of them are flat,what is the finishing process with that type of stone because if we ran a tamper over them i think a lot of them would crack. when i say difference in size some are 3" on one side and 4" on the other with spaces in the the middle and weigh 100 lbs or more

Answer
Michael:
First you have to do a 3-4" crushed aggregate base just like concrete pavers. Compact this first. Then, since you have 1" differences in stone thickness, I would advise a 1.5-2" sand setting bed. Screed the sand with a 2x4. Use 1.5-2" wood strips on either side to ensure sand thickness. Then  you quite literally have to set each stone by hand. Set the stone, tamp it lightly and see if it rocks or is uneven/un-level. If it is, then lift the stone and shift sand as needed. Often you will have to excavate the sand and shifting it around with your hands or a small trowel till each stone sits reasonably level. Keep lifting and then setting the stone till it is just right. Tamp only lightly with a rubber mallet on a scrap 2x4 that spreads the force of the blow across a larger area. Do not ever run a compactor directly across the stones, as you suspected, they WILL CRACK. If you are not happy, you may consider laying a sheet of 3/4 inch play wood over a large section of the stones and run a small plate compactor, but this is still a little risky...I have not done this personally but have heard of it being done.

Good Luck,

Sean J Murphy,
LA, ISA
www.seengineering.com
www.sei-us.com
www.amenityarchitects.com