How to Install a Flagstone Paver Patio

A backyard patio can be so much more than a slab of concrete. Follow these step-by-step instructions to create an affordable outdoor oasis in your backyard using flagstone pavers.

Flagstones, bricks, or pavers make it possible for a backyard concrete patio to be more than a cold, gray slab. Select a location in your yard and sketch a basic plan. Before you break ground, contact your local utilities about locating any underground lines, pipes, or cables. Also decide which method you'd like to use to install your patio: sand or mortar. This piece covers both methods. 

Choosing Flagstone

Flagstone is fractured or cleft into flat slabs of various lengths, 2 inches or more thick, with random edges. The flagstone most commonly used for patios includes bluestone, limestone, redstone, sandstone, granite, and slate. Irregular shapes suit flagstone to both casual free-form and formal geometric design schemes. Cut stone is flagstone finished with straight edges and square corners. It ranges in size from about 1 foot to 4 feet across and comes in different thicknesses.

Whatever type of flagstone you choose, it must be at least 2 inches thick to avoid breakage. A ton of stone covers about 120 square feet; order 5 percent more for breakage. Large stones cover a surface more quickly than smaller pieces but may prove harder to move, cut, and design. 

Unlike ceramic tile, you can set flagstone in a sand base. A mortared installation, however, will give you years of maintenance-free service. A mortared patio requires a slab to provide a solid base. Cleft stone installations require an exterior mortar, generally Type M (which has high compressive strength) or Type S (high lateral strength).

What You Need for the Sand Method

  • Sledgehammer
  • Yardstick
  • Shovel
  • Crushed limestone or gravel
  • Tamper
  • Builder's sand
  • Rake
  • Edging
  • Utility knife or saw
  • 10-inch metal spikes
  • Flagstones, pavers, or bricks
  • Polymer sand (optional)

Step 1: Remove the Old Patio

Determine the size and shape of your new patio. Wear safety goggles and use a sledgehammer when removing the old patio.

Step 2: Excavate Accordingly

To facilitate drainage, excavate the area to a depth of at least 8 inches. The finished patio should be level with the surrounding yard. To determine how deep to excavate, add 6 inches (4 inches compacted base plus 2 inches sand) to the thickness of your flagstones. Our flagstones were 3 inches thick; we excavated to a depth of 9 inches.

Step 3: Add a Base

Add base material. Gravel is good, but crushed limestone works even better to prevent settling. The deeper your base level, the less you'll see your patio shift during winter.

Step 4: Create a Solid Foundation

Tamp after adding a couple of inches of base material to ensure a solid foundation. The compacted base should be 4 inches deep.

Step 5: Add Sand for Drainage

Level a 2-inch layer of builder’s sand with a rake. Sand helps with drainage and makes it easier to position the pavers and level the patio.

Step 6: Install Edging

Install edging around the perimeter of the patio, anchoring with 10-inch metal spikes. Cut and bend the edging as needed.

Step 7: Add Paving Materials

Lay your paving materials over the bed of sand. Slide the individual pieces close together for a clean look; leave bigger gaps if you'd like to plant groundcover, such as creeping thyme, between them. Tamp them gently with the mallet to secure them in the sand.

Step 8: Fill Spaces with Sand

Fill spaces between pavers with builder’s sand or polymer sand. Because polymer sand acts like mortar when it’s wet, it will keep pavers more firmly in place than traditional sand. It also discourages weeds and keeps sand from washing over pavers after rainstorms. Sweep off excess sand after you fill the spaces.

What You Need for the Mortar Method

  • Hammer
  • Small sledgehammer
  • Brick set
  • Carpenter's pencil
  • Mason's trowel
  • Rubber mallet
  • Mortar box
  • Sponge
  • Shovel
  • Mortar bag
  • Height gauge
  • Flagstone
  • Mortar
  • 2x lumber

Step 1: Mix Mortar

Lay out your pattern in a dry run next to the site. Mix enough mortar for about a 3x3-foot section, and trowel a 1-inch thickness on the slab. Then lift your stones from your trial run and set them in the mortar in the same pattern.

Step 2: Lay Stones

Set the larger stones first, keeping them in the pattern and using a height gauge to set them at consistent height. Push the stones down; don't slide them. Fill voids with smaller stones, cutting the stones to fit and leveling them with a rubber mallet.

To cut the stones, mark a cut line on the stone. You can freehand the line or set an adjoining stone on top of the stone you want to cut. Score the line with a brick set. Tap and move the brick set a bit at a time along the line. Then set the stone on a pipe or another stone, then break the stone with a single strong blow. Remove any excess stone along the contours of the cut line, shaping it with the sharp end of a mason's hammer.

Step 3: Level and Let Cure

Check the stones for level—pull out low stones, add mortar, and reset them. Tap down the high stones. If tapping them down won't level them, lift them and scoop out just enough mortar to make them level. Clean off any mortar spills with a wet broom before you lay the next section. Don't wait until you've finished the patio—the mortar will set on the first sections and you won't be able to get it off. Let the mortar cure three to four days, then mortar the joints.

Step 4: Fill Joints

Mix mortar in a mortar box and fill the joints using a pointing trowel or mortar bag. The bag squeezes mortar through a spout into the joints—it's less messy and will reduce cleanup chores. Clean spilled mortar right away with a wet sponge. When the mortar holds a thumbprint, finish the joints with a striking tool. Cover the surface with plastic or burlap (keep burlap wet) and let it cure for three to four days.

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