On Sat, 28 Apr 2012 03:38:47 -0700 (PDT), Hank
wrote:

On Apr 26, 11:55*pm, wrote:
I'm wanting to put a 20 foot concrete pad in front of my garage. *Right
now, the garage floor is concrete, but the driveway in front is just
dirt. *However, under that dirt, there is a bed of 2" to 3" rock, which
I put there about 6 years ago. *What I want to do is just make forms and
have 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 the
rock underneath. *(or the drive will be higher than the garage floor).
Not only will this disturb the well packed base, but will double the
cost of this job, because of the cost of the gravel, and the cost to
rent some sort of machinery to dig up this dirt and rock base, since I
already tried a shovel and with that rock base, the shovel wont even go
in the ground unless it's after a rain when it's muddy, and even then
the 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 at
the front edge of the concrete garage floor (I left the dirt about 4
inches lower than the garage floor intending to pour concrete, but made
that ramp out of stacked 2x8's to drive in and out of the garage). *Add
a few bricks with some rebar on top, And pour/finish the concrete.
A fairly simple job. *However, someone told me I must put dravel under
it first. *Is this gravel really needed? *If it is, why? *After all, I
already have the rock base, which is very solid, and rock is like
gravel. *It's just that dirt has filled in around the rock so it just
looks 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, so
each section is 10ft. *I plan to place one of those black fiber strips
where it meets the garage slab. *I'll probably just trowel the joint in
the middle, to avoid having to rent a concrete saw.

Finally, did I figure this correctly?

20 X 12 = 240 sq ft. *At 4 inches think, I estimated that I need
roughly 3 cubic yards of concrete. *(Actually 2.96 cu yd). *Is this
right? *(I'm not the best at math).

Thanks

Many times gravel is used to bring the grade up to a 4 inch pour.
Gravel is cheaper than concrete. Sand may wash away from under the
concrete. I advise against using sand unless you are sure it won't
wash away.


Wash away??? Yes it can but not common.


Rule of thumb is figure 1 yard will do 80 sq.ft. at 4 inches. So, your
math is correct.

One more thing to think about is to drop the concrete approx. 1 inch
below the entrance of the garage floor. This will serve 2 purposes.
One is that water won't enter under the garage door if you get a
sudden wind driven down-pour of rain. The other is if there is a cold
snap and the outside concrete heaves up a little.


1 inch to me sounds like a lot but I guess a judgement call. I think
you have a good suggestion at least for water tho I still would try to
slope the driveway away from garage if possible. I've seen driveways
in NY and I haven't seen heave problems but I suppose it's possible,
just haven't seen it. Good suggestion tho to ?? inches below
entrance to garage.



Since the pour is only 20x12, I wouldn't worry about the gravel for
drainage too much if you have a good slope to the pour ( 1 inch in 10
ft ).

I wouldn't drive on it for at least a week, 3 weeks is recommneded. Do
not let anything heavy, like a car, sit in one spot very long. Even
after a year of curing, a heavy object will cause the concrete to
develop low spots ( puddles).



That's what I would have thought (about the one week) but I've seen
industrial setting where light traffic was allowed after just 3 to 4
days. I think I heard it's ok because concrete is about at half
strength then. I know I was very nervous when I first learned of
this. Regardless, three weeks is overkill for most residential
driveways unless you are going to have a lot of turning or heavy
vehicles other than cars.