Slab depth of concrete?

[Kirby]

We are ready to frame and pour a slab for an 8 x 8 Hot tub which needs to be 36" from existing ground in order to match the rim of new decking. The site is slightly sloped requiring us to cut into the slope a bit so this would lower the base to 36". We were planning on using 6-8" of baserock and filling in the rest with concrete and jsut making the pad very thick and reinforcing with rebar.

Is there going to be any problems with the concrete this thick? Are there any suggestions on a better way of solving the heigth issue?

Thanks :?

[Rich]

A consideration would be to form and pour 3 sides or use block on the 3 sides. Then backfilling to the required height and placing the slab on top of that.
Could you frame up a deck to hold the hot tub? You could use 6x6 treated posts on pads - use 2x10 joists at 16" o.c. and some type of planking.

[Kirby]

Thanks for the suggestion on using walls. How do I determine how thick the walls should be? Is there a way to form it so I can pour the walls and slab at the same time? I will check out the deck idea also. Thanks

[Rich]

There is a way to pour the wall and slab at the same time - but you will need to leave some wood underneath the concrete. You could form the outside - backfill with as steep a slope as possible leaving at least 6-8" at the bottom away from the form. You will want to compact the backfill as much as possible. A real pain, but viable solution, would be to backfill into the forms and compact it - then dig the 8" walls out. Like I said - a pain.

[Kirby]

Will the concrete set up OK if I stick with original plan and pour it thick? Would there be any sturctural concerns with this idea? I do have access to some labor help so if the cost savings is significant then I like your idea of backfilling the entire area and then trenching out for an 8" wall.

[Rich]

There are no structural concerns with your 1st option. It'll take a bit to fully cure (28 days) but you could probably start setting heavy weight on in 14 days. You're probably looking at around 5-6 cubic yards at somewhere around 70 / yard so maybe somewhere around $400 for the concrete at full depth. Cut it down with backfil and you'll probably cut that in half depending on how well the trenching goes.

[Dano]

Problem with leaving the wood forms is that it breeds termites. Seen it once too often.....