Rebar In A Concrete Slab

Q: I am installing a concrete driveway and have been told that I should put some metal rods in the concrete, but nobody seems to know what size and how many. Can you help?

A: Adding rebar, which is the trade term for the metal rods that are embedded in concrete help prevent the concrete from cracking due to contraction and expansion. The rebar should be laid out in a grid that covers the driveway area and be in the middle of the slab. For details on the size of the rebar and how to position it, follow the link at the bottom of this entry.

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Price Of Concrete

Q: We are thinking a concrete slab out the back door then maybe some sod adjacent to that. My first question is: what does a 10x10 or 10x20 concrete slab cost? I have no clue. Pardon my ignorance!

A: The price of concrete is somewhat dependent on where you live - $110 to $150 a cubic yard, delivery is usually around $50. In some areas there is a minimum delivery of 2 to 4 cubic yards. That is the concrete only, forms and re-bar are extra.

To calculate how much concrete you will need follow the link:

Q: This is exactly what we were looking for - an actual calculator. You should of seen all these "mathematicians" sitting here at the dinner table tonight. One last question: a slab patio rectangle (10x20), what thickness? My father in law stated 3 1/2 inches or 4 inches deep should be plenty. Is this correct?

A: I wouldn't go less than 4" - don't forget the wire mesh or rebar.

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Rebar, Wire Mesh or Fibers in A Concrete Slab?

The great debate on whether to use rebar or number 10, 6 x 6 wire mesh in a concrete slab may go on forever. However, the consensus of opinion seems to be that wire mesh sheets, not rolls, should be used where slab thickness is between four and six inches and rebar should be used in slabs with thicknesses of eight inches or more. The wire mesh should be raised to between one third and one half of the thickness of the slab from the bottom. This can be done by using supports prior to the pour or by raising the mesh after the pour.

Individuals who find that their concrete slabs are cracking with the use of wire mesh may not be compacting the subsurface adequately before pouring the concrete slab. Secondarily, a spacer to help with stress cracks should be placed every 10 feet.

The use of fibers in concrete does not replace wire mesh or rebar. Fibers will aid in preventing surface cracking, but do not provide much in the way of support for thermal expansion or shrinkage of the entire slab.

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