If you live in the United States, you can call 811 to connect directly to your local utility companies.

If you don’t have rope, you can also set boards on the ground to make your outline. You may also spray paint the ground directly to draw the perimeter of the slab.

After placing the stakes, you can move the rope. Avoid putting the stakes directly where you want the corners of your slab since you’ll need to level the ground extending past the slab to ensure it doesn’t sink. If you have corners of the slab that butt up against your home, only place 1 stake in the corner so it’s in line with the side perpendicular to your home.

Mason’s string is braided and thicker than a regular string to help it stay straight. You can buy mason’s string from your local hardware store. Make sure you tie the string at the same height on each stake so the string stays level. If it helps you, draw lines that are 2–3 inches (5. 1–7. 6 cm) down from the top of each stake so you have a reference mark.

This works due to the Pythagorean theorem, which states the squares of a right triangle’s sides total the square of the longest side. For example, if the sides of the triangle are 3 and 4 feet (0. 91 and 1. 22 m), then 32 + 42 = 25. Then, find the square root of 25 to determine the longest side is 5 feet (1. 5 m).

For example, if the side of your slab is 12 feet (3. 7 m), then multiply 12 x ⅛ = 1 ½. Move the string on the stake down by 1 1⁄2 inches (3. 8 cm). You do not have to slope slabs if they aren’t directly next to your home.

If you have dead spots in your yard, fill them in with the clumps of grass.

Even though the strings mark the edges of your slab, dig 6 inches (15 cm) out from them. That way, you’ll create a larger base so the slab is less likely to get damaged as it ages. If you’re digging for a large slab, try renting an excavator instead so you don’t get as exhausted.

You can buy a hand tamper from your local yard-care or hardware store. You can also rent an electric plate tamper that vibrates and automatically compacts soil as you move it around. If you don’t tamp the soil, the slab may sink further into the ground as it settles.

If you don’t want to get your level dirty, lay a straight board on the soil and set your level on top of it.

For example, if your hole is 12 ft × 10 ft (3. 7 m × 3. 0 m), then your calculation would be: 12 x 10 x ½ = 60 cubic feet (1. 7 m3) of gravel or crushed rock. Avoid too small or too large gravel. You want something that’s small, thin, flat, and that compacts well together. Depending on how big and heavy the slab might be, it’s a better idea to fill the whole with 1 ft (0. 30 m) of rock.

Transporting gravel or crushed rock can be really tiring, so ask someone to help so you don’t get too exhausted. Otherwise, try to take frequent breaks so you can stretch and relax.

Wetting the gravel helps smaller pieces sink in deeper and makes the subbase more compact.

You can usually rent tampers from your local hardware store if you don’t have your own. If you don’t compact the subbase, then the gravel may shift or settle over time and cause the concrete to crack or sink. When you’re finished, there should be around 2–4 inches (5. 1–10. 2 cm) of space from the subbase surface to the top of your hole.

Always check the gravel with a level because even though it may look flat, it may be more crooked than you think.