Why? If I ask about my heater not working people will reply?

Are you the heater guru?
Yeah I think that 4" should be thick enough, A driveway is only 4" thick without any rebar & it supports my 2 vehicles fine so I hope that this pad will do the same for my spa.
It was poured on tuesday so I figure that it's safe to place the spa back onto the pad on saturday. I don't plan on filling it up for at least another week after that though. Hopefully it will all go smoothly & the spa will work as it should.
BTW, thanks for responding
