Tools & Materials
With all the beauty of a well-manicured lawn but without the maintenance, a stone patio makes an elegant addition to any home. A variety of flat stones will do—smooth squares of slate or rough flags of limestone—as long as they can withstand foot traffic and the local climate. For most of his patios, This Old House landscaping contractor Roger Cook favors 1 ½- to 2-inch-thick bluestone, a tough sandstone quarried in New York, Pennsylvania and Vermont.
“Setting stone is similar to laying bathroom tile,” Roger says. You prepare a base, level each piece, and fill in the joints. But while tile can be set with one hand, laying a 100-pound stone slab takes brawn and is best handled by two people. “You only want to move them once,” Roger says, “so take your time to set each stone straight with uniform 3/8-inch gaps between them.”
Laying Stone Patio OVERVIEW
Sketch out the project on graph paper first to minimize cuts, stagger the joints, and estimate how much amterial you’ll need. Bluestone comes in rectangles and squares—from 1- to 4-foot-square peices., in 6-inch increments. One ton of stone dust, for a 1-inch setting bed, will cover about 200 square feet. A ton of pack laid at 3-inches will cover 75 sqaure feet.
Align delivered stone near the side where you will finish the patio so you don’t have to retrieve materials over just laid stones.
Rent a skid-steer loader to clear away debris and dig the patio base.
Locate and mark any in-ground gas, electric, water or phone lines by spray-painting the ground.
If you live where the ground freezes or drains poorly, dig down at least 12 inches to save your new patio from being heaved by frost. Those living in mild climates where the soil is sandy and drains well should excavate down to 6 inches.
Excavate the Site
Drive 3-foot stakes into the ground 1 foot outside the corners of the patio area.
Set a builder’s level in the middle. Find a benchmark—a spot where the patio meets the house. Look through the level’s scope while a helper holds a leveling rod at the benchmark and moves the rod’s marker until it falls in the scope’s crosshairs.
Then, at any stake, have your helper, with the marker at the established point, move the rod up or down until the marker falls in the crosshairs.
Mark the stake at the bottom of the rod. Swivel the level and repeat at each stake.
On the two stakes farthest from the house, measure down from the mark 1/8 inch for every foot between it and the benchmark. The marks show the finish grade.
Dig 6 to 12 inches below finish grade to reach the subgrade. Tamp it with a plate compactor.
Set the Base
Cover the subgrade in batches of 3-inch-thick layers of pack, a blend of ¾-inch crushed stone and stone dust. Dampen each layer with water to keep down the dust.
Compact each layer with a plate compactor. Use a hand tamper near walls, sidewalks, or foundations. Repeat process of adding, dampening and tamping each 3-inch layer until all the pack is roughly 2½ inches below the marks on the stakes (if laying 1 ½-inch-thick stone).
Drive additional stakes every 2 feet between the corner stakes closest to the house and again on the opposite end of the patio, which the grade slopes toward.
Stretch a chalk line between the finish grade marks and snap the line against the new stakes.
Run strings along the pitch of the patio between the new stakes at their finish-grade marks.
Tip: For irrigation lines or outdoor electricity, lay 3-inch-diameter PVC conduit over the subgrade.
Spread Setting Bed
In a wheelbarrow, mix one part dry cement with 12 parts stone dust to use as a setting bed for the bluestone. Slowly add enough water to make a stiff mix.
Starting in one corner, shovel out enough mix to lay one stone. Level the mixture with a rake or hand trowel. Depending on size and weight, bluestone slabs will settle into the wet mix half an inch or more, so spread the mix thicker than its planned final thickness.
Check bed thickness by measuring the distance between it and the string. For 1½-inch-thick stones, that distance should be roughly 1 inch, to allow for about ½ inch of settling.
Add or remove mix to meet the finish grade.
Lay the Stones
Lower the stone, smooth face up, into the setting bed. You’ll need two people to handle stones weighing 100 pounds or more.
Twist the stone slightly to put it firmly in contact with the bed.
Then tap the slab around the edges and in the center with a rubber mallet to set it firmly into place.
Tip: Safely “walk” heavy stones into place by holding an edge on the ground and shifting the weight from one corner to the other.
Level the Stones
With a level, check the edges of the stone to make sure they are flush with any adjacent slabs, and check the strings to make sure the stone is pitching at the correct angle. The stone face should be as close to the string as possible without actually touching it.
To adjust a stone for flush and pitch, pry it up with a square shovel, then use a trowel to add or remove wet mix.
Repeat the same shoveling, laying, twisting, and tapping procedure for the next stone, leaving a 3/8- to ½-inch gap between stones.
Lay a level across both stones to ensure they are in the same plane.
Brush and rinse the stones before the wet mix has a chance to dry.
Keep off freshly laid stones for a day or until the setting bed hardens.
Cut Stones to Fit
Mark the cut with a pencil on the top face, then scribe the cut-line using a carbide-tipped awl. For straight cuts, use a level as a straightedge to guide the scribe.
Elevate the edge that will be cut off by placing a piece of wood under the cut-line.
Put on safety goggles, ear protection, and a dust mask.
To score a slab, set the saw blade to a ½-inch cutting depth, start the saw, and slowly guide it along the cut-line. Then set the blade to 1 inch and make another, final pass.
With solid premium-grade bluestone—which is less likely to flake or chip—a scoring cut halfway or three quarters of the way through is sufficient. Just knock off the waste side with a hand sledge. A cheaper, lower-grade stone that’s prone to fracturing has to be cut all the way through.
Fill the Joints and Edge the Patio
While a patio doesn’t need edging to hold the stones in place, cobblestones are an option.
To install them, dig a trench far enough into the pack to accommodate a 4-inch bed of concrete and set each stone 3½ inches below finish grade.
After the patio is firm enough to walk on, spread stone dust over the stones and sweep it into the joints and along the edge.
Using a hose, spray the joints gently with water to encourage the stone dust to pack tightly. A mason’s pointing trowel also helps to tamp wet stone dust into the joints.
Repeat until the joints are firm and level with the face of the stone.
Roll out the chaise and have a well-deserved lemonade.
Tip: Avoid filling joints with cement, or they’ll pop out in winter; and don’t use sand, which can attract ants and give grass and moss a place to grow.