Build a Flagstone and Stone Block PatioUpdated: Feb. 21, 2023
Construct a poured concrete and stone patio with a curved stone wall.
You might also like: TBD
- Multiple Days
Step 1: Overview of flagstone patio ideas
You can’t beat stone as a building material for a backyard terrace. It blends well with any back yard and garden, it’s always in style and it will last almost maintenance free for generations. We built the walls in this project from blue ledge stone and the flagstone patio from cut and squared bluestone.
Stonework is a big job, so we kept our flagstone patio at a smaller, intimate size, about 300 sq. ft. This size is perfect for a small dining table, a few chairs and a barbecue—all in all, a nice space for a family of four and for occasional entertaining.
The modest size means you can complete this flagstone patio installation on weekends and in evenings without heavy professional equipment. We added the low, curved stone wall to enclose one end of the flagstone patio and provide plenty of informal seating. That’s the perfect place to position an outdoor fireplace to chase the chill on cool spring and summer evenings.
In this article, we’ll show you how to build handsome, durable stone walls and lay smooth, close-fitting flagstone. If you enjoy building challenges and don’t mind heavy work, this project’s for you. But give yourself plenty of time. Figure on about 14 full days to complete it, or about a solid month of evenings and weekends. It’s an advanced project because it requires meticulous work and patience to choose the stones and fit them together.
If you have experience laying pavers, working with stone or pouring concrete, you should be able to follow our step-by-step photos and complete this project successfully. You’ll want an extra hand for the heavy work—excavating, pouring the concrete footings and moving stone to the patio site. But you can do the rest of the work solo.
Materials for this project were expensive (close to $7,500), but keep in mind that it will last virtually maintenance free for decades. If you want, you can easily cut the cost in half by selecting less expensive stone. Labor and stone costs vary, but a contractor in our region would charge about twice our cost for this project.
One 3′ x 18″ step stone
300 sq. ft. flagstone
10 tons gravel
2 tons sand
48 lin. ft. edging
75 sq. ft. wall stone
16 lin. ft. capstone
Twenty 4 x 6 x 16 concrete blocks
1-1/2 yds. concrete
100 ft. of 1/2-in. rebar
Step 2: Tools
You’ll need basic masonry tools—trowel, masonry hammer, 4-ft. level, line level (Photo 2), small whisk broom and jointer (to smooth capstone joints; Photo 18).
A wheelbarrow will work just fine for mixing mortar by hand. In addition, you’ll need four specialty tools—a diamond-edged masonry blade for your circular saw, a hand tamper, a plate compactor for compacting the gravel and a dead blow hammer for setting patio stones. Other than that, break out your digging shovels and go to work.
Step 3: Design to fit your site
Relatively flat sites are the easiest to build on. The more sloped your site, the more you have to excavate, fill and build retaining walls and steps. Our project is set on a gentle slope just out the back door. The wall on the low end does double duty. It allows us to build up the grade slightly to form the flat patio. And because the wall rises about 16 in. high above the patio surface, it makes for comfortable seating (Figure A).
We incorporated one 6-in. x 3-ft. long stone slab step between the two walls to transition back down to the natural slope of the yard. Keep in mind that these walls are designed as decorative walls, not retaining walls. If you need more than one step or if you have a steeper slope, have an architect or engineer detail the lower part of the wall to handle the extra pressure.
Our wall is made from mortared stone that rests on a reinforced concrete “floating” footing (Figure C). This type of footing works well for walls up to 2 ft. high and less than 20 ft. long built on “average-to-good” soils—that is, sand, gravel and stable clay. But it won’t do on soil rich in organic matter or expansive clay. You’ll need a deeper footing in those cases. Call in a local structural engineer or architect to review your plans.
The flagstone patio rests on a 6-in. thick gravel and sand bed that you prepare exactly as you would for a brick or paver patio (Figure B).
Sketch out your plan and call your local building inspector to see if there are any permits needed or setback requirements for patios in your area. Also call the local utilities (you can call 811 anywhere in the country) and have them mark their lines before you start digging.
Step 4: Find stone at a landscape or masonry supplier
A landscape or masonry supplier will carry the best selection of stone. For our wall, we selected blue ledge stone. Although technically categorized as a 4-in. veneer stone, it has a random shape that’s ideal for our “rubble-style” wall.
This stone is sold by the ton, and the supplier will tell you how much wall surface 1 ton covers. Calculate the number of square feet of wall surface and add about 20 percent for waste. This project required 5 tons.
For best results, buy bags of mortar from a local masonry supplier. Figure on a bag for every 3 sq. ft. of wall. Also order 4 x 8 x 16-in. solid concrete blocks to fill in wall areas that the patio will cover (Photo 9).
The wall cap is 3-in. thick Indiana limestone that we had custom-cut at a stone shop to fit the radius of our wall with a 1-in. overhang on each side. The capstone for the two walls was expensive (over $1,000), but it made smooth, attractive seating. You can make your own from flagstone, or form and pour concrete capstones for much less. Just keep in mind that a cap at least 3 in. thick looks best.
Buy your 1/2-in. steel reinforcement (rebar) and form building materials for the wall footings (Photos 6 and 7) at a home center.
Select a flagstone patio stone that’s at least 1 in. thick and can withstand seasonal changes in your climate. We used patterned New York bluestone. It’s cut at the quarry in 6-in. increments, ranging from 12 x 12 in. up to 36 x 36 in. The stone varies in thickness from 1 to 2 in., which is why you set them on a sand leveling bed (Photo 20). Bluestone is sold by the square foot. Calculate the area that your patio will cover and add 5 percent extra for waste.
Order a “compactible” gravel, called Class 5 limestone in this region, for the 6-in. thick patio base. Calculate the volume you need and order it along with enough sand to cover the base an inch deep. We selected granite sand because its color is similar to the bluestone color and makes the joints less noticeable.
You’ll also need paver edging to retain the patio edges. You can find all the patio materials at a landscape supplier. You’ll also need seven 1-in. diameter x 10-ft. long rigid pipes and a straight 10-ft. 2×4 for grading the patio base.
Step 5: Paint out the patio to define the space
Photo 1: Establish square lines off the house
Set a string line perpendicular to the house using the 6-8-10 (3-4-5) triangle method. Position it along one edge of the patio. Drive a stake in the ground about 20 ft. out, tie off the string, then double-check the angle.
Detail of measurement
When the diagonal measurement is 10 ft., the string is perpendicular off the house.
Photo 2: Establish the slope
Set the end of the string closest to the house at 1/2 in. above the desired grade level. Pull the string tight from the other end, level it with a line level, then lower the end 2-1/2 in. (1/8 in. per ft.) to set the slope.
Start your project by establishing the height of the finished patio and its slope (for good drainage) in relation to your house and existing yard. We wanted the basic outline of our patio to line up at a right angle to the house, so we started by staking a reference string at a right angle to the foundation (Photo 1).
Use the 3-4-5 (or 6-8-10) triangle method to make an exact right angle. That is, measure 6 ft. along the foundation of the house and 8 ft. out on the string, then adjust the string side to side until the distance between those two points is 10 ft. The string will then be perpendicular to the house. Once you set the string to the height and slope of the patio (Photo 2) and roughly mark its shape with paint (Photo 3), you can determine where to dig and where to build up when you excavate for the patio and wall bases.
In general, keep your patio relatively flat (1/8 in. per foot slope for drainage), allow at least one step up to the house (we had four), and use steps and/or walls to help the patio blend into a sloped yard (we used both). Leave the string in place throughout the construction as a reference for digging out the soil, building the base and setting the patio stones.
Step 6: Excavate the patio
Photo 3: Excavate the patio and footings
Measure and mark the patio and wall positions with marking paint. Use a string and center stake to mark the curved wall. Dig out the flagstone patio to 9 in. below the string line. Dig footings for the walls 12 in. below the grade at its lowest point. Level the footing bottoms.
Photo 4: Check the depth
Check the excavation for depth and level at a right angle to the string. Use a long straight 2×4 and a 4-ft. level.
Using the reference string, roughly mark the patio dimensions and wall positions for excavating (Photo 3). To make an even curve, drive a stake at the center, tie on a string and swing an arc around the stake. Unless your plan is precise, you have some flexibility here. Move the stake or change the string length to modify the arc until you get the shape and position you want.
Hand digging is a lot of work, but for a patio this small it’ll go quickly (Photo 3). Be sure to remove all the sod. If you can’t find a spot on-site for extra soil, rent a 10-cu.-yd. container. (Make sure to tell the container company that you’re putting soil in it!)
Measure the 12-in. depth for the concrete footings at the lowest spot along the wall layout so they’ll be completely out of sight when you’re finished. Dig them about 5 in. oversized (2-1/2 in. per side) to leave room for the concrete forms. Then add the gravel base (Photo 5).
Tip: spread a 2-in. layer of gravel across the entire flagstone patio excavation for a cleaner working surface while you build the walls.
Step 7: Build the footings
Photo 6: Build the forms
Form the 2-ft. wide curved footing with 7-1/2 in. wide strips of 1/4-in. hardboard and 1×2 stakes set every 2 ft. Screw the hardboard to the stakes and level the top. Form the straight wall with 2x8s.
Photo 7: Lay rebar in the footings
Space three rows of 1/2-in. rebar evenly across each footing. Splice pieces by overlapping them 2 ft. and connecting them with two pieces of tie wire. Slip stones under the rebar to hold them 2 in. up. And add 20-in. long rebar crosspieces to keep the rows aligned (Figure C).
Pour the wall footings about 7-1/2 in. thick (Figure C). They don’t have to be works of art, just level and flat. Rip 1/4-in. hardboard into 7-1/2 in. strips to form the curved footing (Photo 6). It’s a little flimsy for holding concrete, so stake it and pile a little gravel along the outer edges to stiffen it. Don’t worry if the form distorts a bit. It’ll be completely covered.
To keep the footings from cracking, it’s important to place steel rebar correctly, about 2 in. up from the bottom of the footings (Photo 7). Keep everything aligned with crosspieces spaced every 2 ft. Then calculate the volume of concrete you’ll need and order it from a ready-mix company. Have wheelbarrows and extra help available on concrete delivery day!
When you place the concrete, make sure it flows around the rebar without leaving voids. Leave the top of the concrete pour rough (Photo 8). It’ll bond better with the wall mortar.
Step 8: Build the straight wall first
Photo 9: Follow the string lines
Drive in pairs of 1×4 batter boards on each end of the straight wall. Angle each board inward to match the wall taper. Tie string lines 10 in. up from the bottom as guides. Dry-fit the stones, starting from the corners. Then spread mortar and set each stone. Move the lines up as you work.
Photo 10: Set each stone in a 1-in. bed of mortar
Spread a 1-in. bed of mortar over each stone and against adjacent stones. Fill gaps between stones as well. Set each stone so the mortar oozes out but doesn’t drip down the wall. Fill open areas inside the wall with mortar and scrap stones.
Flagstone patio installation
Selecting and arranging the stones to create a nice-looking design can be challenging. It’s something like working a jigsaw puzzle. Relax and allow plenty of time so you won’t feel rushed.
- To begin, spread out as much stone as you can, separating it into four groups (Photo 12):
- Thin stones, which are great for leveling rows.
- Medium-sized stones (3 to 5 in. thick) to use as fillers between the large and thin stones.
- Large stones, which you space throughout the wall as dramatic features.
- Corner stones, which will have two faces that meet at a 90-degree angle. Corner stones are the most important, because the wall corners are the toughest to fit and build.
Start with the short, straight wall; it’ll introduce you to basic wall-building techniques. The key here is to keep the wall straight. You might think you can do this by eye alone, but don’t try it. Set up string lines to guide stone placement and to make sure they taper inward toward the top (Figure C and Photo 9). Use your level to set your batter boards accurately. And draw lines on the concrete to help position the first row of stones.
Begin by selecting and dry-fitting the corner stones and a few intermediate stones. Insert concrete blocks where soil will cover the wall (Photo 9). They’re much cheaper than the stone. Now set the stones aside (keeping them in order) and mix up a sack of mortar to a thick, but not stiff, consistency. A properly mixed batch of mortar will stick to the stone; test it to get it just right. If you set a stone and all the mortar oozes out, it’s too wet. And if it’s difficult to push a stone into position, the mortar is too stiff. Mark a bucket to show the amount of water needed to make a perfect batch of mortar. Then use this amount every time you mix a bag.
Set the corners first, then fill in the zone in between. Lay about an inch-thick bed of mortar under and between stones and squish it down to 3/4 to 1/2 in. by tapping each stone with the trowel handle (Photo 10). Hold each stone in position for a few seconds to give the mortar a chance to grab. If the stone drops out of position, remove it, scrape out the old mortar and reset it in new mortar. You may have to slip in a stone chip (shim) to keep it in place. Make adjustments right away. Any movement after the mortar stiffens will weaken the bond.
We fit our stones together fairly tightly, but wider gaps will look fine too. The key is to strive for consistently spaced joints throughout the wall. After the mortar stiffens (your thumb should barely leave an imprint when pressed against it), rake it away to leave a shadow line (Photo 11). That will make small variations in joint width less noticeable. Remember to completely fill all joints, especially the vertical joints. And let the mortar stiffen under each stone before you set another on top.
Use a variety of stone sizes to create a handsome pattern. Large stones make nice focal points and cover a lot of wall area fast. Set a few of these, then fill in between them with small and medium stones until they’re even with the tops of the large stones. Stagger the vertical joints.
As you work, always think ahead about how the next stone will rest on the one you’re setting. If the top of the stone tips slightly inward, following the desired taper, the next stone will be easier to align and set. In general, keep the horizontal joints close to level. And move the guide strings up as you go to keep the taper smooth. Leveling the top of the wall calls for extra care (Photo 15). Plan the last few layers of stones so you don’t have to put extremely thin stones on top to level it off. Frequently check the wall for level; the stones can fool you.
Balance Colors and Shapes
When you’re building a stone wall, think of it as a composition rather than as just stacks of rocks held together with mortar. Mix colors and sizes so the wall is pleasing to the eye. Frequently step back and visualize where you’ll place the next stone and where you want more color. Always stagger vertical joints and keep the joint sizes equal.
Step 9: Build the curved wall
Photo 12: Follow radius lines drawn on the footings
Draw outside and inside radius lines on the footing with a tape measure hooked over the center stake. Start at one end and dry-set a variety of sizes and shapes around the curve. Then set them in mortar. Use 4 x 8 x 16-in. concrete block in areas that will be covered.
Photo 13: Check the radius as you work
Check the radius for each stone with a tape measure. Taper the wall slightly inward by shifting the top edges of the stones in about 1/2 in. per foot of height. Keep the stones roughly level. Rake the joints as the mortar stiffens.
Photo 14: Set large stones first
Chip away the edge of stones with the glancing blow of a mason’s hammer to get a better fit. Stagger the vertical joints by at least 2 in. when possible. Set large stones first and fill in the spaces with smaller ones.
The curved wall is somewhat easier to build than the straight wall, because slightly misaligned stones won’t be as noticeable. Since the curved wall is so long, start building from one end (Photo 12).
You can’t work off string lines. Instead, use a tape measure to check the position of each stone (Photo 13). And check the taper by holding your level plumb along the edges and measuring over to each stone.
Occasionally you’ll have to break a stone to get a nice fit. Hold the stone in your hand and strike the edge sharply with a mason’s hammer (Photo 14). That’ll usually do the trick. If not, set the stone on a soft surface (sand) and hit it harder. Wear goggles to protect your eyes from flying stone chips.
Step 10: Set the capstones
Check the top of the wall for level and mark the highest spot. Plan to set your first capstone at this spot and squish this mortar joint down tight. Then you’ll level the other capstones from it.
Dry-set the capstones on the wall and fit them. Leave a 3/8-in. space between each stone for mortar, or wider if you’re using irregular-shaped stone as a cap. You’ll probably have to cut a capstone or two to make the overhangs on the ends just right. But avoid small stones. Then remove the stone at the highest point and reset it in a bed of mortar.
Gently tap it with a dead-blow hammer or rubber mallet to level it in all directions. Set each stone, leveling off the first. On the straight wall, tilt the capstones about 1/8 in. to one side to drain off water. Work quickly. You won’t have much time to position and level the stones before the mortar begins to set.
After you set adjacent stones, fill the vertical joint between them with mortar, let it stiffen, then smooth and round the joint with a jointer. If you slop mortar on the wall when you set the caps, wait until it dries. Then clean it off with a stiff brush.
Step 11: Build the patio base
Photo 16: Screed the gravel
Pack 4 in. of gravel over the patio area with a plate compactor. Add 3 more inches and set 1-in. dia. x 10-ft. long pipes to slope the grade for drainage. Fill in more gravel and screed it to the pipes with a long, straight 2×4. Pack again.
Photo 17: Spread and screed granite sand
Reset the pipes and double-check your slope. Make minor adjustments by slipping sand under the pipes. Then spread granite sand between the pipes and screed it off even with the tops. Remove the pipes.
There are two steps to building the patio: setting a solid base at the right height (grade) and laying the stone. Setting the grade takes some planning, because you don’t want water to puddle anywhere on the patio.
The reference line we set in Photo 1 sets the slope away from the house along one edge of the flagstone patio. However, you also want to make the center of the patio higher so it’ll shed water off both sides and keep water from pooling along the curved wall. Photo 16 shows how we set the slopes.
Begin by spreading a 4-in. layer of gravel over the entire flagstone patio surface and tamping it with a plate compactor (not shown). This machine is heavy; make sure to ask for operating instructions at the rental yard. If the gravel is dry, sprinkle it so it will pack more firmly. Then spread another 3 in. of gravel and set 1-in. pipes to establish the slopes to ensure good drainage (Photo 16).
First, nest pipe (A) into the gravel so it’s 2-1/2 in. below the string reference line. (This allows for 1 in. of sand plus 1-1/2 in. for the stone thickness.) Now snap a chalk line in the gravel down the center of the patio for a “ridge,” and set a pipe (B) at a right angle to the lower end of the reference line pipe, sloping it upward toward the ridge about 1/8 in. per foot. Slope a pipe (C) down the other side.
Use Photo 16 to see how this fits together. Then, working from the lower areas, slope diagonal pipes (D) to drain water away from the house and away from the curve in the wall. Finally, fill in between the pipes with additional gravel and screed it flat with a long 2×4. Take your time. Accuracy pays off here. Then remove the pipes, fill the grooves and pack the gravel with the plate compactor.
Repeat the pipe-positioning process on top of the gravel, adjusting heights as needed to establish the slopes (Photo 17). Then spread enough sand to cover the pipes and screed it flat. Remove the pipes but don’t pack the sand.
Now set the guidelines for the patio stone. Measure and snap a line on the sand parallel to the house along one edge of the patio, then snap a line perpendicular to the first line by measuring over from your reference line (Photo 18). Use these lines to keep the edges of the flagstones in alignment.
You’re ready to start setting stones. Lay the first row along the line, marking the patio edge, then build up, working in a pyramid shape (Photo 18). The stones won’t quite fit together as easily as a jigsaw puzzle. You’ll have to trim an occasional stone with a circular saw and a diamond blade to maintain even joints (Photo 22). Trimming is a lot of extra work, but the results are worth it.
Step 12: Lay the bluestone
Photo 19: Place the stones
Lay stones in a random pattern. Limit continuous joints to about 4 ft. Strive for a mix of small and larger stones. Make all joints the same width.
Photo 20: Even out the stones
Check each stone with a straightedge. Pull sand away for thick stones and add sand for thin ones to make their edges flush with those of adjacent stones. Anchor each stone with a few whacks of a ‘deadblow’ hammer. Planning to buy one? Make sure you check out this Estwing Dead-blow Hammer.
Photo 21: Mark cuts in place
Cut stones to keep the layout regular and the joint width even. Mark the stones to be cut in place, using a framing square and grease pencil or crayon.
Photo 22: Cut stones with a circular saw
Cut the stone with a circular saw and a diamond-grit masonry blade. Wear eye protection. Control the dust by spraying the blade with a mist of water from a garden sprayer.
For a professional-looking flagstone patio:
- Keep your joint lines straight. The chalk lines snapped on the sand will guide you. If joints begin to wander, snap more lines.
- Stagger joints and limit continuous joints to 4 ft. (Photo 19). Before you set a stone, think about how you’ll set the next two around it. Scratch the size of the stone in the sand before you set it, to see how it’ll work.
- Keep your joints consistent. We fit our stones tightly, only about 1/8 to 3/16 in. apart. But it meant we had to cut a lot of stones to fit. Use slightly wider joints, 3/8 to 1/2 in., for less cutting.
- Mix large and small stones. Set a large stone and work off it with smaller ones. Spread large stones throughout the flagstone patio. Resist the temptation to use all the large stones first.
In general, the stones will follow the slopes you set when you flattened the sand. However, the stone thickness varies, and you’ll have to adjust each stone by adding or subtracting sand (Photo 20). This can be slow, fussy work. Use the surrounding stones as a gauge and make the edges flush with one another. It’ll take some trial and error to set each stone just right and make it stable. Sometimes just cramming sand under one edge with the butt end of a hammer will fix a wobbly stone. Otherwise, remove it and adjust the sand. Make sure not to leave one corner too low.
Photos 21 and 22 show how to mark and cut a stone. Don’t try to make a curved cut where the flagstone patio stones meet the curved wall. Instead, make multiple angled cuts to roughly follow the curve.
Paver edging around the perimeter holds the stone and sand in place (Photo 23). Cover the edging with topsoil and grass or a flower bed to conceal it.
Set the stone step last, because it’s easier to match the step to the flagstone patio than the patio to the step. Set the top flush with the patio, but tip it slightly forward to shed water.
Finally, sweep the joints full with granite sand. It’ll take some muscle to get the sand in. Then wash off the excess with water and save some to refill the joints that settle.
Required Tools for this Project
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
- Circular saw
- Line level
- Safety glasses