So, I’d like to place an 8′ square spa slab on an existing sloped patio slab, so I have a level area for the spa.
I thought I’d just form it like this, with 2.5″ at the top end, and around 5″ at the deep end, and put one course of rebar around the outside, maybe even a layer of wire, and tie it in to the bottom slab with some big tapcons or similar set half in to the patio slab.
Anyone have any other advice ? We’d just hand mix this on site .. regular redi-crete ?
Replies
Sprinkle the area of the pour for 1/2 hr the day before.
Spray an adhesive ADmix on the area just before the pour.
Cover the pour with plastic as soonas you're done finishing it. seal the edegs to the base (concrete/dirt) to prevent evaporation.
Leave for 7 days. OK, if you're really, really in a hurry, three days.
Mist the new 'crete if moisture stops condensing on the bottom of the plastic.
Otherwise, youse has gots a good plan.
SamT
yep, yep, I was going to do all that, except for the adhesive ad mix.
if there is a cart & carry ready mix place around... I'd sure look into haul'n a trailer of concrete vs mix'n by hand... even power mixing in my big machine i can only do about 4cf an based on your size you'll need right at a yard... which is what most trailers are some are 1.25yds... around here it's $90 for the 1.25yds
just my 2cents if it's an option
p
I came up with .3375 yards. I took two of the forms and stacked them, added everything up and divided by two.
concrete... 81sf @ 4" per yard .... 60sf @ 6"... per drawing you'll use over 2/3 of a yard...
the stuff you buy bagged is not the most well mixed stuff... if you get 2000psi out of it i'd be surprised... mix away...
p
Hi Joe, haven't see you for awhile.
I don't know what is under that, in the existing slab for reinforcement.
Where I am going with that is that the strength from rebar you need is in opposition to the loads you will be placing on the minislab, disregarding what currently exists. You show the rebar around the perimeter, but I presume the load will be placed in the middle, so I would suggest tying four more lengths in there, two each way so that you have a grid of nine squares formed by the bar tied.
but if you have a well engineered main slab, this one is just a shim, and then all you would really need is the wire and plastic cover. If you have a way of drilling in larger holes than tapcons, I would, but again, all you are doing is keeping it from sliding downhill.
If you are in a frost area, get some polyurethene caulk to seal the perimeter thrity days after pouring this. You don't want wter sliding between main slab and this shim slab and then freezing. The caulk will keep most water out of that bond plane
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for your dimensions I came up with .75 yards. (8x8xaverage thickness in ft)/27
That is a lot to mix by hand, even with a power mixer unless it is a good sized one. It's around 30 80# bags of sacrete. 33 to be safe.
I did exactly what you are doing only my slab went from 2.75" to 1". I laid a piece of plastic on the concrete - it was stamped and I didn't want to ruin the slab, then built a form and set in on the plastic, caulked the form to the plastic with silicone since it has relatively low adhesion, then poured. I used bagged concrete, and mixed in a small electric mixer. I still had difficulty getting the last bags mixed up before the first started to set. Maybe that was 'cause I ran out :-). I didn't go through all that other stuff, although I did cover it with plastic for several days. I did dye it to match the dk gray stamped concrete. It's held up OK for 5 years with the full hot tub on it. I don't see any reason to put rebar, etc in it, I mean the slab below should be supplying enough strength. The wedge shaped pad will be in compression only - not tension - unless the slab below breaks...
yep, this is only a shim to level it up. I wonder how thin I could go at the uphill end ? I bet the slab doesn't actually pitch as much as my example drawing does.
Frost ? what's frost ??
Funny how we have three diff estimates for the concrete .. who's right ?
I am :-)
Matt
Funny how we have three diff estimates for the concrete .. who's right ?
Matt is.
With 8'x8'x2.5"~5", I got 0.74yds.
Ponytl is real close at "over 0.66yds," but I don't know how. (60sf @ 6" = 1.111 yds)
SamT