Diary of a Flagstone Patio

Curious to learn how experienced professionals install a flagstone patio? See how it’s done with a detailed, step-by-step explanation.

Several years ago, clients asked me to design a flagstone patio to expand their outside seating and to take advantage of their stunning country views.

The project was a collaboration between the homeowners, me, and the award-winning landscape design-build company, Landscapes East.

Here is a documentary of the building process.

Before: The Existing Site

As you can see, my clients already had a lovely deck. But it did not provide enough room for their grill, kids, dog, friends, and large family gatherings.

After several drawings, conversations, and meetings, we decided to go with a 12′ x 18′ rectangular flagstone patio design that could be expanded as a “phase two” project if desired.

Patio Installation: Day 1

Gerry (project foreman) and Kyle from Landscapes East arrived on site with their equipment and materials.

First, they met with the homeowners to verify the location of the septic system and leach field.

Then, using a copy of my design plan, they spray-painted the approximate dimensions of the patio onto the turf grass (lawn), planning to excavate an area larger than the patio’s final dimensions.

The excavation created enough space for deep layers of crushed stone and a sand base, incorporating a gradual slope away from the house for proper water drainage.

The next step was to put down a layer of strong plastic fabric, which is the same type that is used for building roads (not the typical “landscape” fabric, which is too thin).

This fabric helps to stabilize the layers of stone and sand beneath the flagstones, which minimizes settling and shifting. The is especially important in cold regions where freezing and thawing can cause a lot of movement.

Using a laser transit level, they placed metal pins in the fabric to provide a guide for the stone base height.

After that, they filled the area with crushed stone (sometimes called “crusher run” or “crush and run” or “runner crush” (and no doubt other things). They watered this layer with a hose and tamped it down heavily with a tamping machine and a hand tamper to eliminate settling.

Substantial tamping is a key part of the building process that will ensure that the patio will remain exactly 7″ below the last step of the deck and will not sink down over time.

Gerry and Kyle then laid a system of pipes on top of the crushed stone that enabled them to create a perfectly level bed of sand using a screed (wooden board dragged across the pipe rails).

Patio Installation: Day 2

The homeowners chose a material for the patio called “thermal” flagstone. The thermal process creates a smooth surface on the face of the stone using heat. The stone is then machine-cut in modular units and at a uniform thickness.

This is a natural stone with subtle color variations of soft grays, blues, taupes, and browns.

I love this product because it is both contemporary and classic at the same time. In fact, I can’t think of a home where this stone would not look fantastic. It is a major investment for sure, but one that will stand the test of time.

Gerry and Kyle worked together to lay down the stone in a beautiful design that appears to be random. Yet, they meticulously placed each stone to enhance the coloration and overall design.

They avoided any configuration where four corners of stones would meet at the same point, to add stability to the construction.

I wasn’t surprised when Gerry told me that he played Tetris as a kid.  Nor was I surprised to learn that he has been doing this for 17 years, and that Kyle, “the new guy,” has already installed over 50 projects!

After the flagstone went down, Kyle put down landscape fabric to line the gravel drip edge.

I believe that most houses can benefit from having a gravel drip edge border. But it must be installed properly to maintain the correct slope for water drainage away from the house (some folks mistakenly dig out this area to fill with stone, but that creates a trench for water to accumulate, which is not good). 

Good gravel borders can aid against termites and prevents a build-up of moisture near the foundation.

You can plant in front of a gravel edge to make it less noticeable. Or, just leave it alone as a clean-lined feature of your landscape.

Mowing the grass next to gravel is easy as long as the border has a clean-cut clean edge to separate the stone from the lawn. You can also use some kind of edging material to maintain the separation, but care must be taken in choosing a solution so as not to create mowing headaches.

In this case, the 2′ gravel drip edge will accept the water coming off the roof, preventing it from landing directly on the patio, which could wash out the material in between the joints over time.

The gravel for the drip edge is called “#3” size river rock, and it matches the muted tones of the stone in the patio. This is something that you can buy yourself from a large landscape or garden center, and it really gives a high-end, finished look.

At one corner of the patio, I designed a curve to provide extra gravel area to receive the water runoff from where the deck roof and house roof meet.

The gravel drip edge continues around the entire deck and back of the house to create unity in the design and ease of maintenance.

Patio Installation: Day 3

The next piece of the patio construction was the installation of the plastic edge restraints, which are held in place by large metal spikes.

These restraints keeps the flagstones tightly locked into place and prevent the joints from expanding over time.

For the final step, Kyle brushed polymeric sand in between the joints. This is the best product to use for locking in the construction and preventing weeds from germinating in the crevices (mostly from air-born seeds).

Note: polymeric sand is not the same thing as regular building sand or stone dust.

Now the area was ready for grading with topsoil, to smooth out the transition between the patio and the surrounding lawn.

The final result? We think it turned out fabulously. Time to fire up the grill!

Many thanks to my clients and to Landscapes East for allowing me to photograph this project, and for sharing their experience and expertise.

This post appeared previously on The Simple Landscape blog.