How necessary is gravel under concrete?

tangerine3 · 2012-04-27T03:55:10+00:00

I'm wanting to put a 20 foot concrete pad in front of my garage. Rightnow, the garage floor is concrete, but the driveway in front is justdirt. However, under that dirt, there is a bed of 2" to 3" rock, whichI put there about 6 years ago. What I want to do is just make forms andhave a just have a few yards of concrete delivered, to trowel myself.The base dirt is well packed and solid from years of driving on it. To add gravel, I will have to disturb this well packed dirt with therock underneath. (or the drive will be higher than the garage floor).Not only will this disturb the well packed base, but will double thecost of this job, because of the cost of the gravel, and the cost torent some sort of machinery to dig up this dirt and rock base, since Ialready tried a shovel and with that rock base, the shovel wont even goin the ground unless it's after a rain when it's muddy, and even thenthe rock base could not be dug up with just a shovel.My plan was to simply make forms, remove the small wooden ramp I made atthe front edge of the concrete garage floor (I left the dirt about 4inches lower than the garage floor intending to pour concrete, but madethat ramp out of stacked 2x8's to drive in and out of the garage). Adda few bricks with some rebar on top, And pour/finish the concrete. A fairly simple job. However, someone told me I must put dravel underit first. Is this gravel really needed? If it is, why? After all, Ialready have the rock base, which is very solid, and rock is likegravel. It's just that dirt has filled in around the rock so it justlooks like dirt now.One other thing. For a 20 foot long by 12 foot wide strip of concrete,how many joints should I cut in the concrete? I'm thinking just one, soeach section is 10ft. I plan to place one of those black fiber stripswhere it meets the garage slab. I'll probably just trowel the joint inthe middle, to avoid having to rent a concrete saw.Finally, did I figure this correctly?20 X 12 = 240 sq ft. At 4...

Apr 27, 2012 21 Replies

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Cynthia O. 8 years ago

replying to tangerine3, Cynthia O. wrote: Rebar sits in chairs. The newer chairs do not require wire ties around the rebar, and are optional. At least 2 rows of rebar, placed parallel, and equal distance in the concrete footer, are required. WWF is used in slabs, and also sit in chairs to keep it off the ground and at the correct height.

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