concrete slab for water feature/patio

[mikef]

I'm installing a water feature and patio. The water feature is fairly large - about 12'x5' and holds about 150 gallons (about 1300 pounds).

My concern is how thick to make the concrete slab and how to reinforce it. I was planning on putting in a 4" concrete slab over 3" of quarter minus (gravel). Putting rebar in on 12" centers as I've read in other posts on this site. However, the size of the water feature has me concerned about cracks showing up. Should I do a 6" or 8" slab or is that overengineering it?

Also, should I have an expansion joint between the fountain slab and the patio slab to avoid cracking - or again, is that over engineering things? It's easier to just pour it all at once.

Mike

[Rich]

1300 pounds is really not all that much over that area. Most general purpose concrete mixes are 3000-4000 psi. As long as your base material is compacted there should be no problems. Where cracking will occur in a monolithic pour is at the sharp edges of turning the slab up to form the wall and where it turns from the wall to the patio elevation. Make those areas step back at a 45 degree on the non-visible side ( :D ) and thicken the edge at the bottom of the wall.
I would also suggest putting in control joints at 4' o.c. much like a sidewalk. You can then caulk them. This will put the cracking where you expect it anyway.
Hope that helps.