Here's How: A Durable Flagstone Patio Is Attractive

James Dulley on Mar 27, 2025

Dear James: My small concrete patio has some fine cracks but is overall sound. When I enlarge it with flagstone, can I put flagstone directly over the existing concrete patio? -- Sophia T.

Dear Sophia: With its unique variations in shape and color patterns, flagstone is an extremely attractive natural patio material.

Since its shapes are so irregular, it can look out of place when combined with other geometrically shaped materials such as brick, pavers or solid concrete.

Flagstone gets its name from the way it is produced, not from the type of mineral rock that it contains. Flagstone is "flagged" (cut into layers) from common rocks such as sandstone, bluestone, limestone, slate, etc.

You are in luck. Flagstone can be laid over concrete, so you will not have to tear out your old patio. It can also be laid over a sand bed or directly on the bare ground. Since you are going to align flagstones when you enlarge the patio, a sand bed under the extended areas would be best.

You will find that most retailers sell flagstone by the square foot, which is often difficult to measure accurately. Calculate how many square feet of flagstone you will need and then increase it by 10%. The extra 10% should cover the waste from shaping the stones and ones that you will break.

Take your time selecting them to find ones that kind of fit together already. The flagstones that you are laying over the enlarged sand base should be about 2 inches thick for strength. The ones that will be laid over the strong concrete patio can be a maximum of 1 inch thick. This will make them easier to handle and to shape to fit together nicely.

First, work on the flagstones that will cover your existing concrete patio. Lay out the stones over the patio and cut them with the chisel to fit together. A gap of 1/2- to 3/4-inch between them provides a pleasing appearance.

Mix a standard concrete with 1 part cement to 4 parts sand. Include enough water to make a stiff mixture (one that will form a solid ball in your hands). Lift up several of the fit stones and spread a 1-inch-thick layer of mortar over the patio.

Replace the stones and tap them down about one-half their thickness into the mortar bed. Check them with a level. Now, using a gentle touch, lift the stones without disturbing the mortar bed. "Butter" the bottom of each stone with a thinner cement mixture and replace them into the mortar bed.

After you have done a fairly large area, remove the mortar from the joints between the stones to the depth of the stones. A tuck pointing trowel works great for this application. After several days, you can fill the joints with grout or with sand to match the rest of your extended patio.

Make some forms with two-by-fours around the perimeter of the new extended area. Excavate the area to a depth of the thickness of the stones plus 2 inches for the sand bed. Pour in the sand and spread it evenly. Lightly sprinkle the sand with water to compact it.

Size and position each stone on a small area of the sand bed until you are satisfied with the appearance. Using a wooden or rubber mallet, tap each stone down to about half its depth into the sand bed and check it with a level. When all the stones are set, pour sand over the stones and sweep it into the joints. Spray it with water to compact the joints.

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Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, Ohio, 45244 or visit www.dulley.com. To find out more about James Dulley and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.