Concrete: How thick?


Old 01-08-08, 08:52 AM
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Concrete: How thick?

How thick should the concrete be for an average two-car garage?
and what type of concrete? 3500 or 4000?

Last edited by HockeyFan; 01-08-08 at 08:53 AM. Reason: to subscribe
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Old 01-08-08, 11:32 AM
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4 Inches fo 3500 is fine.
Old 01-08-08, 12:16 PM
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Concrete: How thick?

Much depends on what kind of slab you are pouring.

If it is a "floating" slab that bears on the compacted backfill, is inside of the foundations/stem walls AND is not tied to the foundation/stem walls, then a 4" thick slab that is 3500 to 4500 psi would be good. Wire mesh is recommended. Depending where you are, you may need air entrained concrete for an unheated garage where you have salt exposure. In some areas, a concrete supplier may eliminate guarantees (or even refuse to deliver) for concrete in driveways, pads and garage slabs that is not 4000 psi air-entrained. For strength purposes, a lower strength may be satisfactory, but not avisable because of the minimal extra cost and durability concerns. This method provides a raised edge around the slab that permits easy cleaning and gets the wood up and out of the moisture.

If it is a structural slab that is a part of the support of the walls, the thickness will depend on the depth of the thickened edge. Reinforcement (rebars) will depend on the size, because it is usually assuamed that the soil under the slab portion will settle some and the slab cannot float on the soil, but must span. The strength of the concrete will be somewhat higher and depends on the size (higher for a large garage) but the same durability/salt exposure requirements exist.

In either type of slab, make provisions for a proper drainage path (that can really be built/finished and works) and for crack control. If you do not saw joints immediately (same day if possible) after pouring, you will never be able to properly seal the cracks that will eventually occur not mateter what you put in the concrete.

Do not skimp on the materials, since it can never be made better after it is built.


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