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Old 05-09-2008, 09:32 AM   #1
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pouring a level concrete slab over sloped concrete

We need to pour a level concrete slab to accommodate our new hot tub. This slab will be poured on top of an existing sloped (for drainage) concrete terrace. The size of this pad will be 84" x 84". How thick should the thinnest part be? (the max thickness at the lowest part of the slop will be approx 4" thick) How many bags of premix concrete will it take to do an area this size? Any other things we should know about before pouring this slab? Thank you.


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Old 05-09-2008, 10:36 AM   #2
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concrete premix

You'll have about 16 cubic feet of concrete (less depending on how much slope there is).
Concrete can come in different size bags, so you'll have to determine the amount per bag. (80# bag, 60# bag, 40# bag..) often 1/3 to 2/3 cubic feet per bag. it'll be listed on the bag.

It's a lot of work! If you are in an area where there is frost for part of the year laying a slab on another slab may create problems.



Last edited by harvster; 05-09-2008 at 10:42 AM.
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Old 05-09-2008, 07:11 PM   #3
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7'x7'x4" = 16.33 CU.ft An 80lb. bag yeild 1/2 Cu.ft you will need 32 bags. Minus the pitch of the existing slab. I would pour a bonding agent on the existing slab before I formed and poured the new slab. just my 2 cents .good luck Bob
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Old 05-09-2008, 09:29 PM   #4
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I'd suggest looking in the phone book for a "short loads" concrete supplier, trade lingo for small quantities. You will pay a little premium for the service, but it is well worth it IMO. As you see from the math of others, that is a lot of bags to haul from the big box, handle, and pour. I would start with no less than 3" at the THINNEST part. The level top of the forms will determine the thickness at the down slope end. Use a bonding agent as suggested, and some reinforcing wire, even if just a pieces of "hog wire" from the big box, tied together with baling wire. Keep the wire a couple of inches in from the edge of the concrete and as close to the center of the depth as you can, for rust purposes.
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Old 05-11-2008, 08:55 AM   #5
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your new slab'll weigh enuff so it won't move,,, therefore, i wouldn't use a bonding agent,,, rather, i'd wanna be sure my new o'lay slab did NOT bond,,, 3" at the thinnest - wended wire fabric if you wish but i'd go w/fiber,,, DO be certain your new joints're cut above existing & add as rqd for proper jnt practices,,, if you've never done this type of overlay ( bonded OR unbonded ) work, maybe its best to follow the other posts.
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