Steps for Installing a Flagstone Patio

David Beaulieu is a seasoned professional in landscaping and a skilled plant photographer, boasting two decades of expertise in his field.

Project Summary

• Overall Duration: 1 to 2 days
• Output: Create a 120-square-foot patio using flagstone.

• Proficiency Level: Intermediate
• Projected Expense: Between $1,800 and $2,200

For a long-lasting and classic patio option that harmonizes beautifully with your garden, flagstone is an ideal selection.

This organic substance serves as a patio concept that complements a variety of designs, ranging from classic to contemporary. The greatest advantage is its straightforward installation, as it employs dry-set methods instead of traditional mortared techniques.

What does Dry Set Installation entail?

Dry-set installation involves placing flagstone on a base of stone dust or sand rather than using wet mortar or concrete. This method is significantly more accessible for DIY enthusiasts, as it allows for direct installation on the ground. In contrast, using mortared stone necessitates a concrete slab foundation to avoid mortar cracking.

Dry-set flagstone is installed on a base of several inches of compacted gravel, topped with a layer of stone dust or decomposed granite (DG). Decomposed granite consists of crushed stone, featuring a mix of small fragments along with gravel and sand-sized particles.

Flagstone Pavers Compared to Conventional Pavers

While flagstone pavers are visually appealing, their installation is more complex compared to standard concrete pavers. The uneven edges create difficulties in achieving a snug fit between the stones.

The surfaces of flagstone pavers, both on the top and bottom, are irregular. It is necessary to evaluate each stone separately and frequently make adjustments to ensure that the height remains uniform throughout the patio.

Prior to Starting

Buy flagstones in large quantities by the pallet. A single pallet can cover approximately 120 square feet of patio space and is priced between $1,400 and $1,500.

Choose the biggest stones that you can manage. Sort them to ensure uniform thickness and appearance. For durability, the stones should have a minimum thickness of 1.5 inches.

Safety Factors to Keep in Mind

Dial 8-1-1, the national hotline for Call Before You Dig, to get all underground utility lines on your property identified. This service is complimentary, but it may take a few days, so make sure to reach out well in advance of your project.

Requirements

Devices / Instruments

• Measuring tape
• 8 Wagers
• Compact sledgehammer
• Mason’s boundary
• Line stage
• Shovel
• Rake
• Woodworker’s spirit level
• Manual tamper or plate compactor
• Broom
• Watering hose

Materials

• Compactable gravel
• Crushed granite (granite dust)
• Flagstone
• Material for filling (as preferred)
• Extended, flat 2×4 lumber

Instructions

Outline the boundaries of the patio.

Establish mason’s lines to outline the patio’s boundaries. Place two stakes at each corner, extending approximately 2 feet beyond the edges of the patio. Connect a mason’s line between the stakes on opposite corners to form a square or rectangular shape.

Examine the arrangement for the square.

Verify that the string arrangement forms a square by measuring the diagonal distance between the opposite corners where the strings intersectthe arrangement is square if the diagonal measurements match. If necessary, reposition the stakes to achieve a square layout.

Tilt the Arrangement Strings

Ensure the strings are level and sloped by positioning a line level on each layout string and making necessary adjustments at one end. After that, secure the string in place. It’s important that all strings are at the same elevation. Next, fine-tune the two strings along the edges of the patio to achieve the desired slope. Lastly, modify the perpendicular string at the lower end of the patio to align it with the ends of the sloped strings.

Dig out the patio space.

Clear away all grass and any other plants from the patio space outlined by the strings. Next, dig into the soil to a depth of 6 inches, in addition to the thickness of the flagstone. Use the strings as a reference to measure the depth of the excavation. Compact the soil using a hand tamper or a rented plate compactor.

Set up the gravel foundation.

Place a 2-inch layer of compactable gravel across the patio space. Use a rake to ensure the gravel is even and flat, then compact it well. Add an additional 2 inches, and repeat the smoothing and compacting process. Similar to the excavation process, measure from the strings to check the gravel thickness and ensure the correct slope is maintained.

Incorporate the layer of decomposed granite.

Spread a 2-inch layer of decomposed granite on top of the gravel foundation. Use a rake to even out the decomposed granite, and then level it from side to side using a long board and a level. Compact the layer well. Afterward, take out the stakes and mason’s lines.

Arrange the Rocks

Organize the stones intended for the patio surface on a spacious, level surface, like the nearby lawn or a driveway. Sort the stones by their dimensions and forms to facilitate easy selection while you install them into the patio.

Place the Patio Slabs

Begin by arranging the stones on the decomposed granite surface, starting from one end and progressing to the opposite side. Position the stones as closely as you prefer. The spaces between them will be filled later with sand, gravel, or even soil, along with grass or other vegetation. To achieve a more organic appearance, mix different sizes, shapes, and colors of stones for a more varied pattern.

Even out the stones.

Adjust the position of each stone by adding or removing DG beneath it to ensure stability. All stones should be level with each other and the surrounding stones. Any edges that protrude can pose a risk of tripping.

Complete the Blanks

Use sand, decomposed granite, or gravel to fill the spaces between the stones. Use a broom to distribute the material over the patio, ensuring it gets into the crevices. After that, spray the patio with a garden hose to help the filler settle, and then add more material to the stones to completely fill the gaps.

What are the advantages and disadvantages of using flagstone?

One of the main advantages of flagstone is its authentic appearance, which harmoniously integrates with the surrounding environment. Its suitability for dry-fit installation makes flagstone simpler to work with compared to mortared stones. However, the irregular edges of flagstones can make it challenging to achieve a snug fit, resulting in wider joints.

What is the lifespan of a flagstone patio?

Flagstone patios have the potential to endure for many years due to the durability of the natural stones used. Occasionally, these patios may require re-leveling. If any individual flagstones become cracked or damaged, they can be easily removed and replaced without disturbing the surrounding stones.

Is a flagstone patio more affordable than a deck?

A flagstone patio tends to be pricier than a deck. The cost of natural flagstone is relatively high, with 120 square feet priced between $1,400 and $1,500, translating to approximately $10 to $12 per square foot. In comparison, constructing a ground-level or floating deck typically ranges from $400 to $700.