Site prep -- question regarding my concrete pad

[pg_rider]

We recently added on to our existing 10'x12' concrete patio by adding another 10'x12' section on either side. We did this partly in anticipation of eventually getting a hot tub, although we didn't tell that to our contractor. So, the pads are in and they're great; 4" thick, flat, with a very slight slope away from the house for drainage. My questions:

1) Will that slight slope affect the tub in any negative way? Like I said the pad itself is flat, it just has a slope to it (imperceptible to the eye). I REALLY don't want to have to shim the tub!

2) I just talked to the contractor and in his words "if you'd told me ahead of time it was going to be for a hot tub we'd have put some fabric or rebar in the concrete, but as it is it should still be fine". Should that make me nervous? I know they did a good job prepping the ground (tamping, etc) so I'm not too worried about settling, but could it crack or break?

Appreciate any insight!

Here's a pic of where it's going to go (not sure yet if we're going to put it on the left or right end):

[Reese]

Looks nice, and like a perfect spot to put a tub.  With a 4" thick slab, you should be fine.  The tub will put a couple of tons of weight on the slab, but it will be spread out over a big footprint, so the psi won't be bad.

We put our tub on a pre-existing patio that had a slight slope (approx 1-2"/10 feet)as well.  Just do a little planning regarding orientation of the tub, and you'll be fine.  Our tub has deeper seats on one side of the tub, and with my wife and I both tall, we wanted as much depth as possible.  We placed the deep seats on the downhill side, which leaves the shallower seats facing the yard.  That works well, because those seats benefit from being up higher for the view.  Although the water is closer to the cushions on the downhill side, no one but me notices.  Another option we considered was placing the filter compartment on the downhill side to ensure that the pumps wouldn't cavitate, and give both deep and shallow seats the view.  

If your slope is too much, someone here poured a shallow concrete shim on top of their existing pad, using a poly barrier to allow removal at a later point.  That thread, with pics was on here about a year ago.

[dkersten]

I am no engineer, but if you buy an 8'x8' tub, and fill it with water and people, the overall weight should be around 4500lbs.. the 8x8 area is about 9000 square inches, which puts you at about .5psi.  Now like I said, I am no engineer, but I cannot for the life of me imagine a situation where a half pound per square inch is even a minor stress on a 4" slab of concrete.  Stand on your tip-toes and you are putting 50 times that weight per square inch on that concrete..

The only thing I would worry about would be the overall weight making the slab settle a little, shift away from the house if the ground it was poured on was graded away from the house, or if there are no control joints in the concrete and having the half your tub is on to crack the slab somewhere in the middle.. However it looks like there are control joints there that will take the brunt of any settling or shifting, so I imagine worst case would be that control joint spreading a little..

Rebar or fabric in the concrete will help if you focus a lot of weight on a small area of a slab, like a car tire that is putting up to 2000 lbs on a few square inches.  But since the weight will be distributed evenly on the slab, you dont have to worry about that..

Once again though.. I am not an engineer..

[sledjunkie]

you will be fine