How to Excavate for a Patio, Walk, or Wall Footing
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 below 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.
What You Need
- Round-nose shovel
- Small sledgehammer
- Mason's line
- Plumb bob
- Chalk line
- Marking paint
- Garden hose
- Tape measure
Tip: Laying Out a Curve
Where your patio or walkway plan calls for a curve, lay a charged garden hose (water turned on, nozzle shut off) to mark the curve. Pour sand over the hose (you can use marking paint if you don't mind having a painted hose). Lift off the hose and you'll have an easy-to-follow curved line.
Step 1: Mark Corners
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: Dig Trench
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.
Patio Line on the House
If the patio will abut the house, you need to snap a chalk line under the door at the height of the patio surface. Put it about 1-3 inches below the threshold to keep snow and rain out of the house. The line marks the finished surface of the patio. Use it to set the excavation depth for the entire site.
Step 3: Measure Trench
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: Excavate Interior
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: Measure and Mark Space
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.
Step 2: Dig Trench
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.
Bonus: Know Your Excavating Tools
Most masonry projects require digging and earthwork. Whether you are setting stepping-stones or digging footings for a wall, you will probably have to cut through sod with a spade or lawn edger to remove soil. If you have to remove a large amount of sod—to construct a patio, for instance—rent a power sod cutter.
The sod cutter carves sod into strips and slices under the sod to separate it from the soil so you can roll it up and reuse it elsewhere in the landscape. When you have to excavate a large area, loosen the soil with a garden tiller first to make digging easier. If you have to dig a number of postholes for footings or to build an overhead structure or fence for your patio, rent a power auger. The two-person version in the photo will bore through soil and small roots easily. You can use a hand auger or posthole digger if you have just a few holes to dig.
You'll need a tamper whenever you excavate or fill an area. Sand and gravel base material for concrete and stone surfaces should be tamped too. A hand tamper works well for small areas, but consider renting a power tamper for large patios and long paths or walks. In footings and holes, you can tamp with the end of a 2x4.