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Prep Ground for Concrete...
What You Need
- shovel
- pick
- wooden stakes
- claw hammer
- mason line (or similar string or twine)
- permanent marker
- line level
- framing square
- plate compactor (or hand tamper)
What You Do
Excavation
Dig out the entire area to accommodate a concrete slab that will be 3-1/2 inches deep. How deep you dig depends on whether or not you want the surface of the patio at "ground level" (grade) or slightly above it.
Here are four common examples...
1. Slab above grade with brick border:
2. Slab above grade with slope down to grade:
3. Slab at grade:
4. Slab at grade with pavers on top:
You'll need to add several inches to each side of your excavation area to allow for the 2x4 forms that will be installed. For example, if your slab is going to be 8' x 14', the excavation area would measure around 8' 8" x 14' 8".
Once you have the entire area level, compact the dirt with a plate compactor. Add fill where necessary to bring it back to the depth you want and then compact the dirt again.
Concrete Forms
Drive stakes approximately 6-8 inches beyond each of the layout points. (Since the paint lines were only meant to establish a rough layout, you'll need to re-measure so that all the figures are accurate according to your original design.)
Starting at stake #1, tie string about 4 inches off the ground. Run the string to stake #2, using a line level to determine proper (and level) height from one stake to the other.
Repeat the process of leveling string from stake #2 to stake #3. NOTE: Make certain you create a 1/8" per foot fall to allow for proper drainage for shedding water. (For example, if the width is 8', you'll want one side of the surface to be 1" lower than the other.)
To square the corner, measure 6' off stake #2 in one direction and 4' in the other. Mark each of those points on the string with a permanent marker.
Adjust the string between stake #2 and stake #3 until the diagonal measurement between the two marks are exactly 10'. To make adjustments, simply add an additional stake to move the string one way or the other (see insert A).
Continue to work around the entire layout, using the line level to keep the string level and squaring off each of the corners (in small areas you can use a carpenter's framing square).
Using the string as a guide (both in position and height), construct forms using 2x4 lumber placed on edge. Drive enough stakes behind the forms to prevent them from moving during the concrete pour and then nail the stakes to the form boards.
Fill in and pack dirt behind the form boards. This will not only keep the forms from moving, it will also prevent cement from leaking out when you pour cement.
Things To Consider
Each slab that you pour will require a different direction for the 1/8" per foot fall. In the illustration above, it's assumed that the house is located to the left of the designated slab.
Stakes need to be driven deep enough so they are slightly below the top of the form boards. That way, your screed board will slide properly across the forms when you're initially pulling and leveling the concrete.
Always "soak" the ground with a good spray of water prior to pouring concrete. You don't want so much water that puddles remain on the surface but rather the substraight becomes slowly and thoroughly saturated.
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