building a concrete slab


Old 07-14-05, 09:03 AM
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Exclamation building a concrete slab

I am attempting to build a concrete slab to support a 16X24 storage shed. The slab will be above an old shell driveway, so I have some degree of stability. I think I will use a graded slab, but I have questions...
1. What's the best way to level the ground on which the slab will sit and how do I tell when it's level other than eyeballing it or going through the expense of renting surveying equipment?
2. What should the dimensions of my footing?
3. How much, if any, rebar and reenforcing wire should I use?
4. Will the fact that the old shell driveway is only approximately 2/3 the width of the slab have any impact?(I have to dig down about 3 inches to get to the shell)
5. How many yards of concrete should this job require?

I worked as a helper on a construction crew when I was younger, so I remember how to do some things, but never picked up on the details.. please help.

Last edited by ScottD; 07-14-05 at 09:15 AM. Reason: not finished with questions
Old 07-14-05, 08:33 PM
Join Date: Nov 2001
Location: Taylors, SC
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You can cut the soil off flat with a square nose shovel. Don't remove any more dirt than necessary. You need to pour concrete on undisturbed soil. You can check for level by setting a four foot level atop a long, straight 2x4 and using it to check the surface.

Dig and form footers to the depth recommended locally for your frost line. Your building permit folks will be able to tell you the recommended depth of the footers and what size rebar to use in the footers. If you pour monolithically, set the 6 mil polyethylene on the ground of the slab and set the reinforcement wire on it. Otherwise, do this after you strip the interior forms from the footers. If you will park cars on the slab, raise the wire to the midpoint of the concrete during the pour. You can use spacers to hold the wire in place.

A slab 4 inches thick should work well.

The shell should not matter unless there is so much of it that it is loose, then it should be removed or compacted mechanically.

If the footers are 8 inches across and 12 inches deep, the 16 x 24 slab will take approximately 6 cubic yards of concrete. Allow for waste and inaccuracies in leveling the slab area. You will need 384 square feet of reinforcing wire or about 77 linear feet of wire 5 feet wide. When you order your concrete, tell the company representative the dimensions of the pour so he can check your figures. You don't want to run out during the pour. Short loads are quite expensive.

Be sure to get your inspections at the correct stages in the project to avoid grief later.

Hope this helps.

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