Flagstones are rocks that have been split into slabs and cut into flaglike shapes. They can be of bluestone, limestone, or sandstone. Known as random rectangular flagstones, their sizes start at 12 x 12 inches and increase by 6-inch increments to 36 and sometimes to 42 inches. Thicknesses vary: in an order of 11/2-inch stones, you’ll find stones from 11/4 to 2 inches thick. Flagstones are heavy; move them by handcart or wheelbarrow. Have someone to help lay them.
Flagstones can be cheaply installed (and with reasonable permanence) on a sand bed. After a winter, however, you may have to reset some stones. Laying stones in concrete, although more permanent, is costly and difficult job for a contractor.
The length and width of the walk or patio should be divisible by 6 inches. In ordering, tell the masonry supplier the dimensions. Upon delivery, sort the stones by size; then on graph paper, plot the placement of each stone. Break up any long joint lines; frost heaves are likely along such lines.
Lay out the project with string and stakes. Excavate to 7 inches (4 inches for gravel, 3 inches for sand). Set up formwork, using pressure-treated boards. Spread and tamp the gravel, then the sand. Check both with a level.
Place the stones, leaving 1/2 inch between them. Stand on each to make sure it doesn’t teeter; you may have to lift it and add or remove sand. Tamp all stones with a rubber mallet. Finally, sweep a mixture of half sand, half topsoil into the gaps. Pack it down with a good hosing, then let it dry. Repeat until the joints are filled.