I'm pouring a spa pad 12' X 12'X 4.5" for spa and gazebo total 6000 lbs. I've been told by my local Home Depot I should use 3/8" rebar 12" - 18" OC. My yard has a slight slope (4" over 12') and is mainly clay which is VERY slippery when wet and mushes easily. We've lived here 10 years and after a heavy rain, I'll still sink in 1-2" if I walk on it.

Does the rebar start 18" in from the sides or closer? I've heard back and forth that I should pour additional 6" X 6" footings on all four sides to keep the clay from getting washed out, others have told me a 2" sand and 2" gravel base should be all I need.

I just jackhammered out the pad my last contractor poured because he screwed up and didn't order enough concrete, and tried to level by hand below the form level. The surface was very uneven. He also never tamped or leveled the clay surface and said rebar wasn't necessary. (he did give me my money back) so I'm thinking the old adage (if you want it done right, do it yourself) applies, and I really want to do this right the 2nd time around.

I know by formula I don't need expansion joints, but I prefer them for control (I'm thinking right down the middle, both ways). Even if I end up hiring somebody again, I would like to be more informed about what is the right thing to do.