Why Put gravel under concrete?

mister_friendly · 2010-05-06T07:43:37+00:00

I have poured many small sidewalks and shed floors and never putgravel under the concrete. I want to pour a driveway section in frontof the garage and was told by a guy at the concrete company (who cameto measure the amount needed), that I need to put gravel under theconcrete. WHY?I should mention that I always put lots of small to medium sized rocksunder concrete to save on the amount of concrete needed. I save allrocks I get just for that use, and leave them get rained on to cleanthem. Any rock that will not exceed the height of the forms, goes inthere. Because this will be driven on, I intend to put in some rebar,which I never do on sidewalks and shed floors. I have never had anyproblems with these sidewalks cracking or substantially lifting inwinter.

May 06, 2010 Last reply: 4 years ago 22 Replies

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Rockhead 5 years ago

Appreciably, Alan

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Kevinzep 4 years ago

Good question. 6-6-10 Welded Wire Mesh - It is used often to keep the slab in compression. Concrete has poor tensile strength. Many times the mesh will sink to the bottom of the slab and will be pratically useless unless it is physically pulled up into position after the pour. I prefer #3 rebar at 18" o.c. placed on concrete dobies or chairs especially for driveways and large slabs. Kevin Szczepankowski, HouseArte.com

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