How to Lay a Bluestone Patio

The bluestone that makes up millions of American patios often comes in neatly sawn rectangles. But for a rustic landscape, nothing looks more natural than “snapped” or “broken” bluestone, terms used to denote an irregular edge on the slabs. This Old House senior technical editor Mark Powers recently built a patio out of this hearty type of bluestone in his backyard. As he shows on the following pages, laying a long-lasting patio like his is as much about the base underneath it as the layout above. With a little digging endurance and the patience to piece together a rock puzzle, you, too, can create a gathering space that appears to come from another time.

Stone: 1½-inch-thick broken bluestone, about $240 per ton; Gault

Moss: Fern moss, about $120 for a 25-square-foot box, Moss Acres

How to Install a Bluestone Patio in 12 Steps

Step 1: Get an Overview of the Project

Day-to-Day Timeline:

Friday: Lay out the size and shape of the patio area, and arrange the placement of the stones.

Saturday: Dig out the area, and create the base layer.

Sunday: Position and level the stones, then fill the joints.

Step 2: Create a Layout

Whether you’re building a patio with rectangular slabs or with broken pieces like the one shown here, laying out the stones to perfect your pattern before starting the installation will save headaches later on. Random patterns may require you to cut some pieces to fill in blank spaces.

Using a rope or garden hose, outline the shape of the patio. Beginning on one edge, lay the largest stones around the field; fit smaller stones in between; leave joints of 1½ to 2½ inches.

To cut a stone, flip it over and mark the underside for the cut. Using a grinder fitted with a diamond blade, score along the cutline. Prop up the stone on a stone you don’t intend to use, with the waste edge hanging over, and hit it with a brick hammer to break it naturally along the score. Or set a mason’s chisel in the score, and hit it with a maul to snap the stone.

Step 3: Number the Stones

With the pattern set, number the stones in chalk to note the layout. Keeping the stones in order, stack each row to the side.

TOH Pro Tip: Take several digital photos of the numbered layout from above to help re-create the pattern later.

Step 4: Grade the Slope for Excavation

The patio must slope away from the house or other structure to direct runoff away from the foundation. Grade the slope about 1/8 inch per foot. Keep track by running a mason’s line at the proper slope and measuring down from it as you dig. You have to dig deep enough to remove the dark topsoil layer—how deep depends on the soil conditions in your area. But you must go down at least 6 inches to accommodate the base.

To create a graded line, set stakes a few feet deep at what will be the high and low corners of one side. Moving a level along it as a guide, run a level mason’s line between the two stakes about ½ foot above the ground. Multiply the length of the side in feet by 1/8 inch. Move the line on the low-side stake down by that amount. For example, if the side is 5 feet long, lower the string 5/8 inch.

Set two stakes on the opposite side of the patio. Using a level, transfer the height of the line from the top and bottom across, then connect the sloped line on the other side at the same height as the lengthwise lines.

Step 5: Excavate

Using a spade, dig out the topsoil within the patio outline until the dark loam turns to lighter subsoil (typically between 6 and 12 inches).

Step 6: Set the Stakes

Set a stake every 2 feet along the graded mason’s lines, and run cross strings at the height of the lines, creating a grid across the excavated area. Check the depth of the area by measuring the distance between the new cross strings and the subsoil. Clear high spots and backfill low points until the area is evenly excavated.

TOH Pro Tip: Make a mark on each stake where it meets the ground in case it gets knocked over, then notch the stake to hold the mason’s line without tying it off.

Step 7: Put Down the Base

A patio is only as sturdy as the layers beneath it. Even in a natural design like this one, a sturdy base that drains well will prevent stone edges from popping up and creating a tripping hazard.

Completely fill the excavated area with 3 inches of paver base. Using a hand tamper or compactor, pack the base, keeping it graded to the slope of the mason’s lines. Continue laying 3-inch layers of base and tamping it until the surface measures 2½ inches below the desired finished patio height.

Step 8: Grade your Work

Pour 1 inch of leveling sand over the base. Using a garden rake, smooth the sand and even out the field until the sand is 1½ inches below the patio finish height. Keep track of the grading by checking the depth against the mason’s lines.

TOH Pro Tip: To keep dust down, spray the paver base lightly with a hose before tamping it.

Step 9: Lay the Stone

Bluestone is naturally bumpy, so it’s important to keep it as even as possible to avoid creating a trip hazard. You can check the stones with a level; while they may not always read level, you’ll be able to tell if they’re flush with one another and graded properly.

Lay a row of stones in place, re-creating the numbered pattern you established earlier. Set all the large stones first, placing smaller stones only for reference. Using a rubber mallet, strike the stones to set them in place.

Step 10: Keep It Level

Set a level across the stones two by two, and fill with or remove sand until they’re even and graded appropriately. Fill in with the small stones. Don’t walk on the stones until they’re all in place.

TOH Pro Tip: Create a measuring guide by marking the finish distance between the top of the stone and the grade line on a spare stake.

Step 11: Fill the Joints

Finish the natural look of the patio by planting moss or other plants that can be tread on between the stones.

Hose down the patio to help lock in the stones. Using a garden spade, remove excess pockets of sand in the joints and replace with excavated soil (indigenous moss often prefers this soil to rich potting soil). Clear the stones of excess sand and soil with a push broom.

Step 12: Moss the Joints

Dip dry moss into a bucket of water and press it into the soil. Plant all the joints and around the edges.

Tools