Expert: Stephen Major (Owner--Major Design Group) - 5/20/2007

Question
How thick does the concrete have to be to support a larger hot tub? Does it need reinforcement such as steel rods or can we just prepare the space(dig out the sod and top soil) , create and  set the forms,  level, mix, and  pour into prepared space?  

Answer
Pamela,

I picked up this question from the question pool.  There are a few factors to consider here.  I don't know where you are located, but if it is in a northern area then you need to consider the effects of frost on the stability of the slab.  

Any concrete slab that is supporting a load needs to be reinforced.  The slab should be placed over a well-compacted subgrade, on a layer of crushed stone (for drainage).  At a minimum you should install 6x6 #10 welded wire mesh, to hold the slab together in case of cracking.  A higher quality installation will include a grid of #4 rebar every 24" or so.  Place the rebar grid about 1.5" to 2" up from the bottom of the concrete, and lay the wire mesh on it.  You can get "high chairs" or other similar devices to elevate the rebar during concrete placement.  Even bits of broken brick will do in a pinch.

Best of luck with this, and please let me know if you need additional information.

--Steve Major