Excavating

Learn the basics of excavating for a patio, walk, or wall footing.

Intro

Digging is hard work, even if you've loosened up the soil with a rototiller. If you think the work is beyond your abilities or will exceed your available time, hire a contractor or other willing laborers. Consider this option especially if your local codes require you to dig down to undisturbed soil, as many do.

The procedures illustrated on these pages assume that your project requires forms and the working room to install them. That's why the batter board mason's lines are set a foot beyond the actual perimeter of the project. If your structure doesn't need forms, you won't need the trench.

Be sure to excavate your site to a depth that will accommodate all of the materials needed -- for example, 4-6 inches of gravel, 2 inches of sand, and 3-4 inches of concrete (or whatever the thickness of the finished surface will be).

Because the weight of a concrete slab is distributed over many square feet, it usually doesn't need footings. A slab floats; that is, it moves up and down with the surface as the ground freezes and thaws. But a footing is required to support most walls (except dry-laid stone walls), spreading the weight so the wall doesn't sink. Most codes require footings that are twice the width of the wall and as deep as or deeper than the frost line. Be sure to check your local codes before you pour the concrete.

Prestart Checklist

Time
About one day for one person to dig 100 square feet 6 inches deep

Tools
Round-nose shovel, spade, small sledgehammer, mason's line, plumb bob, chalk line, marking paint, sand, garden hose, level, tape measure, stakes, wheelbarrow

Skills
Digging, laying out, leveling

Prep
Lay out and square the site.

Step 1

To mark the outside corners of the forms, drop a plumb bob from the intersections of the lines. Drive 2-foot stakes at the intersections. Remove the lines but leave the batter boards.

Step 2

Tie mason's lines between the stakes to represent the height of the finished surface. If excavating for a patio, the lines will be level with the patio line on the house. For both a patio and walk, excavate a 1-foot-wide trench outside the lines to the depth your installation requires.

Step 3

Use a tape measure to periodically measure the depth of the trench. That way it will remain consistent, and you'll have a constant reference point when you excavate the interior of the site.

Step 4

Remove the lines but not the stakes. Excavate the interior, removing the soil to the depth of the perimeter trench. To keep the entire excavation at a consistent depth, check it periodically with a 4-foot level or a slope gauge. If you remove too much soil in some places, fill the dips with sand or gravel--not loose soil. Use a flat spade or square shovel to dig the final inch of soil from the bottom and sides of the excavation.

What If ... You're Excavating a Wall Footing?: Step 1

Drive temporary stakes to mark the approximate location of footing corners. Drive layout stakes (or batter boards) beyond the temporary stakes. Then tie mason's lines and square the corners with a 3-4-5 triangle. Drop a plumb bob at the intersection of the lines and redrive the temporary stakes under the plumb bob. Tie mason's lines between the stakes, and paint the ground along the lines.

What If ... You're Excavating a Wall Footing?: Step 2

Using your painted lines as a guide, slice the sod about 6 inches outside the perimeter of the footing and strip away the sod, saving enough to fill in the bare edges of the footing after you've finished it. Then excavate the footing trench to the depth required by local codes, measuring down from the mason's lines to keep the depth consistent.


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