How to Install a Flagstone Patio

Flagstone has long been a desired product when speaking of outdoor patios or walkways. The rustic appearance of the product and the extreme durability of the stone make it hard for any wood, composite, or concrete material to compare to. Flagstone has been used for centuries to build roads, patios, courtyards, walkways, etc. While the dependability of the stone makes it a good choice for landscaping, the colors and textures that nature has to offer make it an exceptional alternative to concrete.


The term “flagstone” has become more of a general term in stone. The actual definition of “flagstone” describes stone from nature that has been split into flat, irregular pieces and shapes ranging in thickness from ¼” to somewhere around 3”. Due to flagstone being a product of nature, it comes in many different types of stone; most commonly sandstone. By the type and color of your flagstone, as well as the method you choose to install it, you will achieve different looks and textures with your outcome.

Setting Flagstone in Soil

Setting natural flagstone in native soil is the simplest way to create a flagstone patio or walkway. This method takes less material and preparation because you are basically setting the stones in the areas that you dig out. This method will yield less formal results and not exactly be the method for an outdoor kitchen or and active patio.

To do this you simply dig out the areas that you wish for the stone to be. After the area has been dug out, you simply set the stones into the excavated area, digging out soil until the surface of the stone is level with the ground. After the stones have been set into the excavated area, take the dirt that was dug out to create the patio, and fill the joints between the stones.

This particular installation will require that you use a flagstone that I no less than 2” thick. This method is generally used when a homeowner wishes to have plants or grass grow in the areas between the stones. The stones can be set as close or as far apart as you wish.

Setting Flagstone in Sand

While the internet and DIY guides show hot to install flagstone using sand underneath the stones and between the stones, Whiz-Q Stone does not recommend this installation what so ever.

We have found that the sand does not stay between the stones and washes out upon a rainstorm or even in lawn irrigation. To achieve this look, we recommend that you use polymeric sand which will actually harden between the stones, making it less susceptible to exit the joints between pieces of flagstone.

Setting Flagstone in Mortar on Bottom

This method is a century old method generally used by the English. This process involves laying a substructure of a compacted base material of decomposed granite, using mortar underneath each stone for leveling. This process will also prevent the stone from sliding or shifting around when being walked on. After the pieces of stone are set in mortar, polymeric sand, decomposed granite or gravel is used in the joints.

To do this type of installation, you first want to excavate out the area you wish the flagstone to be intstalled at a depth of 6-8 inches. This is so you have enough depth for 3-4 inches of decomposed granite for a base, 1 inch of mortar, and a 2 inch thick flagstone.

Once the area has been excavated, bring in the decomposed granite, compacting at a depth of 2 inches at a time. *Do not compact more than 2 inches of decomposed granite at a time. Also remember to slope the sub-base away from the house for drainage purposes. Generally this is done using a ratio for ever 5 feet away from the house, dropping the patio by at least 1 inch. Once your base has been compacted, lay the stones out over the area to see how they will fit.

After laying the stone over the area, mix your mortar and begin to apply approximately a 1 inch thick bed underneath each stone. Use the mortar to make sure that each stone remains level with the stones next to it. Continue this for each stone throughout the area. *Remember to use a 4’ level to check to make sure that the area is level across a series of stones.

Once the area has been set with mortar, use decomposed granite, gravel, or polymeric sand to sweep into the joints between the pieces of flagstone.

This type of installation is ideal for landing areas, walkways, of sitting areas. Generally, this method is still not recommended for large living areas or outdoor kitchens.

Setting Flagstone in Mortar on Top of Concrete

Laying flagstone over concrete is the most preferred method of installing stone. It last longer, hold up to larger amounts of traffic or heavy furniture to grills, and provide a smooth surface to entertain on. While this installation is the most challenging, it will yield the best results and last the longest.

This method can be tricky, so looking for professional help is not a bad thing.

If you have existing concrete to lay flagstone atop of, then the hard part of this process is over. Just remember to check for height restrictions at doors and gates. It is also recommended to clean the slab and apply a bonding agent to help the mortar adhere to the surface.

If you do not have a concrete patio, then you can use a Portland Cement and remix to pour your own. This is virtually an easy process that can be done either using a wheel barrel or a cement mixer. To pour your own cement to lay flagstone atop of, excavate out the area at a depth of approximately 4” (keep in mind that the height of the flagstone will range from 1” – 1 ½”, so if you are trying to match a certain height you may have to excavate 5” – 5 ½”).

Once the area has been excavated, begin to mix the Portland Cement carefully following the instructions on the bag. For smaller pedestrian traffic, you can use a wire grid to lay in your concrete. For larger applications, rebar might be necessary. Once the wire grid has been laid in the area, begin to spread the concrete evenly over the area just as you would gravel. Periodically use a shovel or a pick to pull the wire grid up so that it is in the middle of the cement being poured. Continue doing this until the entire area is filled with concrete. Now make sure the concrete is level and give it 24 hours to set up.

Once the concrete has set up, it is time to lay flagstone. Do this by first laying out the flagstone in small sections at a time to ensure fitment. Once a small area has been laid out, mix your mortar in a wheel barrel and begin to mortar underneath each stone using a shovel. Lay each stone in the mortar pressing firmly in a back and fourth motion to eliminate any air gaps between the stone and mortar. Continue by laying other stones around the first, fitting each stone together like a jig-saw puzzle. You can rearrange the stones and shape each one to fit just how you want. Try to keep all the joints fairly common in size throughout the entire project.

As you continue laying the stone, begin sot “tuck” mortar in the joints between each stone. This can be done using a trowel and basically by packing mortar into the void space between the stones. The mortar can be brushed away and cleaned once it has set up. In this step, you are simply ensuring that the entire void has been filled with mortar and there are no empty spaces present. Continue to do this over the patio, checking the consistency and set up of mortar you had previously done.

To check to see if the mortar can be brushed and finished, use your finger to brush across the mortar. If the mortar smears, then it still needs time to dry. If it crumbles like cheese, then it is ready to be brushed. You can brush the joints using a wisk broom, a sponge, or wire brush. The smoothness of the mortar joint is a personal preference. Basically start in one end and brush each joint, knocking off any excess mortar. This will make your joints look professional and more appealing. One this is done, try to stay off the area for at least 24 hours before using it.

The installation method will give you the most permanent results, and it installed correctly will last for many years of enjoyment.

If you have any other questions about installation, product selection, or any general issues, please feel free to contact Whiz-Q Stone at 817-429-0822 or toll free at 800-648-4551. We have more how-to’s and calculators on our website at www.Whiz-Q.com.