Flagstones are irregularly-shaped pieces of flat rock that fit together like a puzzle. They are commonly used to create residential walkways and patio areas. One of the most important parts of installing flagstone is preparing a stable base for it, so that future shifting and settling does not occur. Although installing flagstone over clay is similar to installing it on other soil surfaces, the thickness of the underlying materials is different.
Mark out the outer edges of the walkway or patio using spray chalk.
Dig into the clay in the centre of the chalk lines using a shovel. Remove all the clay inside the lines to depth of 8 to 10 inches. If the clay is too hard to dig manually, use an air spade, which you can rent from a home improvement store.
Spread a 4- to 6-inch-thick layer of gravel in the bottom of the hole and spread it out evenly using a bow rake.
Plug a soil compactor into an electric outlet and push it over the entire surface of the gravel to compact it tightly. You can rent a soil compactor at a home improvement store.
Spread a 2- to 4-inch-layer of sand on top of the gravel and spread it out using the bow rake. Use the soil compactor to compress the sand in the same manner that you did the gravel.
Lay the flagstones on top of the sand arranging them in any desired pattern. Leave at least 1 inch between each stone.
Shovel sterile soil or sand on top of the flagstones and push it down in between the stones, using a push broom. Continue adding sand or soil until the gaps are filled to the surface of the flagstones.
Water the area to see if the soil or sand sinks. If it does, add additional material to fill in the sunken areas.