Home Improvement Outdoors Decks & Patios

How to Lay a Flagstone Patio

Updated on 04/21/24

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What is Dry Set Installation?

Dry-set installation sets the flagstone in stone dust or sand instead of wet mortar or concrete. It is much easier for do-it-yourselfers because you can build directly on the ground, while mortared stone requires a concrete slab foundation to prevent cracking in the mortar.

Dry-set flagstone is set in several inches of compacted gravel, followed by a layer of stone dust or decomposed granite (DG). Decomposed granite is pulverized stone that contains small pieces and gravel-size and sand-size particles.

Flagstone Pavers vs Traditional Pavers

Flagstone pavers, though attractive, are more difficult to install than traditional concrete pavers. The irregular edges make it more challenging to fit the stones tightly together.

Flagstone pavers' tops and bottoms, too, are uneven. Each stone must be individually assessed (and often adjusted) to keep its height consistent across the patio.

35 Patio Paver Ideas to Upgrade Your Outdoor Oasis

Before You Begin

Purchase flagstones in bulk by the pallet. One pallet capable of paving about 120 square feet of patio costs around $1,400 to $1,500.

Select the largest stones you can handle. Cull them for consistent thickness and appearance. For strength, the stones should be at least 1-1/2 inches thick.

Safety Considerations

Call 8-1-1, the national Call Before You Dig hotline, to have all underground utility lines marked on your property. The service is free but can take several days, so call well before starting your project.

Equipment / Tools

Tape measure
8 Stakes
Small sledgehammer
Mason's line
Line level
Shovel
Rake
Carpenter's level
Hand tamp or plate compactor
Broom
Garden hose

Materials

Compactible gravel
Decomposed granite (stone dust)
Flagstone
Fill material (as desired)
Long, straight 2x4 board

Mark the Patio Edges

Set up mason's lines to represent the perimeter of the patio. Drive two stakes at each corner, about 2 feet beyond the sides of the patio perimeter. Tie a mason's line to opposing pairs of stakes to create a square or rectangular layout.
Check the Layout for Square

Confirm that the string layout is square by measuring diagonally between opposing corners (where the strings meet); the layout is square when the diagonal measurements are equal. Adjust the positions of the stakes, as needed, to square the layout.
Slope the Layout Strings

Level and slope the strings by placing a line level on each layout string and adjusting one end up or down. Next, tie off the string. All of the strings should be the same height. Then, readjust the two strings running down the sides of the patio to set the correct slope. Finally, adjust the perpendicular string on the lower end of the patio so it is even with the ends of the sloped strings.
Excavate the Patio Area

Remove all grass and other vegetation in the patio area (defined by the strings), then excavate the soil to a depth of 6 inches plus the thickness of the flagstone. Measure down from the strings to gauge the excavation depth. Tamp the soil with a hand tamp or a rented plate compactor.
Install the Gravel Base

Add a 2-inch layer of compactible gravel over the patio area. Rake the gravel smooth and level, then tamp it thoroughly. Add two more inches, then smooth and tamp. As with the excavation, measure down from the strings to gauge the thickness of the gravel and to maintain the proper slope.
Add the Decomposed Granite Layer

Add a 2-inch layer of decomposed granite over the gravel base. Rake the decomposed granite smooth, and level it side-to-side with the long board and level. Tamp the layer thoroughly. Remove the stakes and mason's lines.
Organize the Stones

Stack or lay out the stones you will use for the patio surface on a broad, flat area, such as the surrounding grass or a driveway. Arrange the pieces by size and shape so you can select them readily as you lay them into the patio.
Lay the Patio Stones

Place the stones onto the decomposed granite surface, starting at one end and working toward the other. Place the stones as close together as desired. You will fill the gaps later with sand, gravel, or even soil and grass or other plants. Vary the size, shape, and coloring of stones for a random pattern, which looks most natural.
Level the Stones

Level each stone, as needed, by adding or removing DG underneath the stone. Each stone should be stable and at the same height as the surrounding stones. Stone edges that stick up create tripping hazards.
Fill the Gaps

Fill the gaps between stones with sand, decomposed granite, or gravel. Sweep the material across the patio with a broom to push it into the cracks. Spray the patio with a garden hose to settle the fill material, then sweep more filler across the stones to fill the gaps.

FAQ

What are the pros and cons of flagstone?

The greatest benefit of flagstone is its natural look that organically blends with the rest of the landscape. Because flagstone lends itself well to dry-fit installation, it's easier to install than mortared stones. But, due to their irregular perimeters, flagstones are difficult to fit tightly together, so they have broad joints.
How long does a flagstone patio last?

Flagstone patios can last for several decades since flagstones are natural stones. Flagstone patios occasionally need to be re-leveled. Individual flagstones that have become cracked or broken are easy to remove and replace without affecting the rest of the patio.
Is a flagstone patio less expensive than a deck?

A flagstone patio is more expensive than a deck. Flagstone is an expensive building material; 120 square feet of natural flagstone costs around $1,400 to $1,500, or around $10 to $12 per square foot. By contrast, you can build a ground-level or floating deck for around $400 to $700.

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