Design your space and estimate the material
Use garden hoses to represent the patio and wall, and move them around until you find a design and size you like. Use marking paint to establish the outlines (Step 1). To estimate the wall block quantity, begin by pounding in stakes at the highest and lowest points of the wall, then stretch a string with a line level horizontally between the two. Measure down from the string to the sod at the stake on the lower side of the hill, then add 3 in. (to allow for burying the lowest course of block halfway). Round up to the nearest full block to get the approximate wall height. For the length, simply measure the painted wall layout line (Step 1) with your tape. Multiply the length by the height to get the total square feet of wall face. The supplier will calculate the block quantity from the squarefoot calculation. You’ll have some extra because the wall steps down on the ends, but you might need it if any of the blocks are damaged. Figure two corner blocks per row for the ends (Fig. A). Tell the supplier that your top row will be cap blocks.
To order the patio pavers, just provide your supplier with the diameter; they’ll put together a package containing the right quantity of each stone shape. At first glance it might look complicated, but the manufacturer has directions telling how many of each shape to put in each ring. Ask for the paver layout plan when you order; it’s not packaged with the pavers. Allow a week or more for delivery.
Step 1: Position the spikes
Position 10-in. spikes to mark the center points of the patio and wall. Swing a tape measure hooked on the spikes and spray-paint arcs to mark the actual face of the wall and edge of the patio. Paint a second set of arcs to indicate outer excavation lines, adding 2 ft. 4 in. to the wall radius and 8 in. to the patio radius.
Spray-paint the ‘footprints’ of your wall and patio, dig just inside the outer layout lines and then reestablish the center points of your arcs after excavation. Dig about 9 in. below the patio’s center point to provide room for the gravel, sand and pavers. This photo shows you where to measure your depth. Because of the sloping hill, the front edge of the patio will be a little high compared with the lawn. (You won’t dig out as much soil here.) Add soil when you’re done to blend the elevations. The bottom of the excavation has to be flat and slightly sloping (Step 3). Be sure you compact any loose soil. If you don’t, it will settle over time and the patio will end up with a dip.
Step 2: Dig into hill to create flat area
Dig into the hill to create a flat area for the patio and wall. Dig 9 in. below the sod, using a point 3 ft. in from the lowest edge of the patio as a reference point. Hire or rent a skidsteer loader (a Bobcat) to make quick work of removing the bulk of the material. Clean up the perimeter and flatten the bottom with a shovel.
Tools (and the perfect excuse to rent a Bobcat)
You’ll need several heavy-duty tools to do the job right. You’ll have to rent a plate compactor. This 200-lb. beast is the secret of a long-lasting patio. Rent it and move it around with a dolly. You’ll need it for two days: one day to pack the gravel footing for the retaining wall and a second day for the patio.
For excavating, you’ve got two choices: a good shovel and strong back, or a skid-steer loader (commonly called a Bobcat). If you’re just doing the patio, dig it by hand. But for cutting into a hill like we did, a skid-steer is the only way to go. If you’re a tool junkie, you can rent one. Bear in mind, though—by the time you’re done hauling it, learning how to operate it, using it and replacing the neighbor’s hedge you destroyed, you can probably get the job done cheaper and faster by hiring a contractor. A skid-steer loader will rut your lawn, so plan on filling in the path with topsoil and grass seed when you’re done.
To get rid of the excavated soil, you can rent a trash container, ask the contractor to haul it away, fill in a low spot or persuade a neighbor to take it. If you rent a trash container, keep it until you’re finished so you can throw in any extra gravel or sand.
Step 3: Check your patio area using a level
Check your patio area using a straight 10-ft. 2×4 and 4-ft. level. It should have a slight slope (about 1/4 in. every 4 ft.) away from the wall and be level side to side. Use a plate compactor to compact any soil you’ve added or loosened.
Step 4: Relocate the spike that marks the wall center point
Relocate the spike that marks the wall center point; it may take a little trial and error. Spray-paint a new arc 6 in. shorter than the radius of the face of the wall. Then spread a 2-ft. wide swath of base material from this line to the back of the excavation. Start with two 2-in. thick layers, compacting each. Spread about 2 in. more and use your straight 10-ft. 2×4 and 4-ft. level to make it roughly level. Compact again.
Install the gravel footing
A wall is only as sturdy as the base you build it on-in this case, crushed gravel that ranges in size from 3/4 in. down to a powder. Suppliers may refer to this material as crushed Class II or any of a number of other names. Build a 6-in. deep layer by spreading 2 in. of base, dampening it, compacting it, and then repeating the process.
Compact the gravel at least four times. The compactor’s tone will change from a dull thud to a sharp whack and the machine will start to hop when the surface is hard enough. If you’re unsure if it’s packed well enough, pass over it a few extra times. The gravel layer should be 3 in. or more below the sod on the ends of the arc and be within an inch of level all the way around.
Step 5: Spray-paint another arc
Spray-paint another arc, representing the face of the wall. Precisely align and level each block. Cut a notch out of a 14-in. 1×3 to bridge the ‘tongue’ on top of the block for leveling the block front to back. Make slight adjustments by tapping a corner with the butt end of the hammer, and larger adjustments by adding or removing base material under the blocks. If you add more than 1 in. of base material, compact it with the hand tamper before setting the block. Set cap blocks and corner blocks on the ends of the first row. Install landscape fabric to separate the soil from the gravel you’ll use as backfill.
Set the first row of block flat as a pancake—and the rest is easy
Set the first block, level it in both directions, then add the next. Tweak each block when you set it to make it perfectly level. Setting just one slightly out-of-level block will haunt you on consecutive courses. Lay the entire first row. On the ends, place a cap block and a corner block to create a finished look where the wall steps down (Step 6).
Place 4-in. perforated drain tile with fabric wrapped around it at the base of the wall. Bring it from end to end and leave the ends open. Don’t worry about drowning your petunias; water will never gush out. The pipe just relieves water pressure against the wall.
Step 6: Place 4-in. drain tile behind the bottom row of block
Place 4-in. drain tile behind the bottom row of block from end to end. Fill behind the block with 3/4-in. clean, crushed gravel and compact with a hand tamper. Add subsequent layers of block, starting at the middle of the arc. Center the first block over the joint below and work toward each end. Fill behind the wall with gravel after each course and compact with a hand tamper.
Rent or buy a hand tamper for compacting the gravel behind the wall, and get a sturdy contractor’s wheelbarrow for moving those 300-lb. loads of gravel.
Modular blocks stack fast
You’ll amaze the neighbors with how fast the wall goes up. Fill behind each layer with 3/4-in. crushed gravel and hand-tamp it. Don’t use extra base material for behind the wall; it doesn’t drain well. To be sure the gravel continues to drain well, place landscape fabric between the soil and gravel to keep the dirt from mixing in (Step 5).
Before placing each course, sweep off stray gravel on the block below. Since the blocks automatically step back with each layer, the wall’s radius increases with each course. To keep the joints evenly staggered, start setting each row of block at the center of the arc and work toward the ends. Use construction adhesive formulated for concrete block to secure the cap and corner blocks (Step 7).
Wrap the landscape fabric over the gravel and fill behind the top layer of block with soil. Grade the soil so water flows around the wall (Step 7). To prevent water and soil from washing through the joints of the cap block, lay 6-in. squares of fabric over the joints to seal them.
TIP: Lay and compact the gravel for the patio at the same time as the wall. It’ll give you a nice, clean surface to work from when constructing the wall.
Step 7: Secure the cap blocks and corner blocks
Secure the cap blocks and corner blocks with a bead of special construction adhesive. (Wrap the fabric over the gravel before placing the cap blocks.) Backfill behind the caps with soil and compact it with the hand tamper. Slope the soil to drain water around and away from the wall.
Selecting retaining wall block
Our wall is made up of individual blocks that interlock. Think of them as concrete Lego blocks. They offer design flexibility and longevity. We chose a tumbled Roman Pisa block by Interlock because we liked the soft, aged look. But it came at a cost-33 percent more than standard untumbled block. Interlocking block, which has a tongue and groove, is easy to install on curved walls. You use a smoothtopped ‘cap’ block to finish off the top row, and corner blocks with a textured face on two sides to finish off the ends.
Compare block at square-foot prices, rather than by the piece. The small blocks might seem cheap, but when you do the math they often end up costing the same as larger ones. Prices vary greatly per square foot of wall face. Most blocks are 8 or 12 in. deep. Use 12-in. blocks for all but short garden walls; they’re heavier (43 lbs.), but the extra weight ensures a longer-lasting wall.
Ask the supplier what size radius you can make with the block, then make sure it accommodates your design. You’ll have four or five colors to choose from. Lighter-colored blocks will maintain color better than darker ones over time.
If a wall will be more than 48 in. high, has a large hill behind it, or is supporting heavy clay soil, you need additional reinforcement. You may need to install a product commonly called ‘geogrid’ and have an engineer help you with the design.
Step 8: Reset a spike at the center point of the patio
Reset a spike at the center point of the patio and spray an arc 8 in. larger than the radius of the patio. Spread two 2-in. layers of base material over the stabilization fabric, compacting each layer with the plate compactor. Build up the perimeter with soil to keep the base material from spreading outward as you compact.
Laying the base
After excavating, we laid a special woven ‘ground stabilization fabric’ over the patio area. It’s cut off a roll from the landscape supplier. You don’t need it in stable sandy or gravelly soils, but in other soils it’s cheap insurance for a flat patio for years to come.
Reestablish the patio’s center point. Keep the spike in until you start laying the pavers; it’ll mark the starting point for the paver circle. Mark out the patio perimeter plus an extra 8 in. with marking paint. Add and compact two layers of base material in 2-in. layers. Position and slope the screed pipes so the patio will drain water away from the wall (Steps 9 and 10).
The third layer should be no more than 3 in. below the sod at any point. A few inches higher than the sod is better. Add more base material to raise the entire patio if necessary. Slide the 2×4 side to side along the pipes to distribute the base material and create a flat surface. Compact this final layer four times, changing direction each time-north to south, then east to west (Step 11).
Step 9: Set two 1-in. steel pipes on top of the compacted base material
Set two 1-in. steel pipes about 6 ft. apart on top of the compacted base material. Orient them in the direction of drainage, away from the wall. Slip base material under the pipe until a 4-ft. level with a 3/4-in. block slipped under the low side reads level. Set the other pipe level and parallel to the first.
Planing, Paperwork and Materials
We carved our patio into a gradual hill, using the retaining wall to hold back the slope. The main wall is a 30-ft. long arc, 30 in. high. The patio is 11 ft. in diameter. This combination creates a cozy area for a couple to enjoy a cup of coffee or read a book and creates a nice space for flowerbeds and plantings. If you plan to entertain, or want room for the kids to cruise around, you can easily stretch the patio’s diameter to 16 ft. without complicating the job. Increase the wall diameter accordingly.
Most communities don’t require a building permit for patios or for retaining walls under 4 ft. high. They can usually be placed anywhere on your property, which makes them a great alternative to a Planning, paperwork and materials deck in small yards. But keep them out of easements, which are bands of property left open for drainage or for access to buried utilities. Your local building or planning department can tell you, or your survey will show you, if there are any on your property. Review your plans with them to be safe. Also call the local utilities and have them mark their underground lines, even if you don’t think there are any in the area. The service is free and it could save you from an injury or from having to dig up your patio later.
Don’t locate a patio beneath a mature tree. Even though the tree makes for a nice shady spot and nothing will grow under it anyway, the patio can damage the roots (and vice versa). Locate it outside the tree’s canopy; anything closer, consult a tree specialist.
Our expenses came to about half what a contractor would charge. The material costs may vary substantially depending on your location and delivery costs.
We suggest buying all your materials from a landscape supplier and having them delivered. A landscape supplier will have a better selection than a home center and you can see the different styles of pavers and retaining wall block firsthand at the displays in their yard. Plus they can provide expert advice for any questions you might have.
Step 10: Level the base
Shuffle a 10-ft. 2×4 side to side along the pipes as you level the final layer of base material and pull it away from the wall. Fill in any depressions and remove any high spots as you work. Remove the pipes and fill the troughs with gravel.
Laying the pavers—the fun part
Laying the pavers is the easiest and most rewarding part of the project. You’ll need five different shaped pavers to build this circular patio (Fig. C). The manufacturer’s chart tells you how many of each shape to put into each ring. Alternate the shapes if a ring has more than one paver shape.
Since you start in the center and work out, you’ll have to disrupt that flat sand layer with a few footprints. Minimize the damage by staying in the same footprints, then trowel them flat when the paver rings get close. After you’ve laid three or four rings, stand on the pavers and have a helper pass you the next pavers. Don’t step on the very edge or you’ll create a dip. Once you get the first five rings in, it’s pretty methodical and will go quickly.
If you end up with a gap where a ring comes together, distribute it by spacing several bricks up to 1/8 in. apart. To get an even color mix throughout the patio, draw the pavers from more than one pallet. If you’re just using one pallet, you can blend the colors well by drawing from opposite sides; one half is usually darker than the other.
Step 11: Compact last layer
Compact this last layer, making certain the soil is built up on the sides and the base material is perfectly flat.
Step 12: Place the pipes
Place the pipes in the same location as shown in Step 9. No leveling should be needed, since the slope is established from the gravel layer. Repeat the procedure shown in Step 10, using sand instead of base material. Remove the pipes, fill the troughs with sand and trowel the area smooth. Fill in your footprints as you back out. Remove the center spike.
TIP:Wear kneepads to protect your knees from hard paver edges.
Step 13: Position the center pavers
Position the center pavers, then install the outer rings using the shapes and patterns specified in the manufacturer’s plan. Stagger the joints. Use only one footpath as you work so you disturb the sand as little as possible. Stand on the pavers once you have a few rings placed and have a helper pass or throw you the next half-dozen rings. Add a little sand and trowel out the footprints when you reach them with the installed pavers. Work out to the final size.
Step 14: Pull the sand away from the perimeter of the patio
Pull the sand away from the perimeter of the patio with a steel trowel until you reach the base material. Snip the backside of the edging with garden pruners to bend it to the arc of the patio. Hold the edge restraint tight to the pavers, then drive 10-in. long, 3/8-in. spikes every foot through holes in the edging. Connect the edging, leaving no gaps between the pieces.
The final details
To contain the pavers and sand, install a paver edging around the perimeter (Step 14). We used Snap-Edge. It costs a little more, but it installs easier and offers better support than less expensive alternatives. Before installing the edging, be sure to scrape the sand away to expose the base material. Conceal the edge with soil or mulch when you’re finished.
Run the compactor over the patio to set the pavers, compact the sand and vibrate sand up into the joints, locking the pavers together (Step 15). The steel plate won’t hurt the pavers, but it will make your ears ring. Wear hearing protection. (If a paver does break or chip during this step, gently wiggle it out with a pair of flat screwdrivers and replace it.) Spread coarse, dry sand over the patio to fill the joints and repeat the compacting. The sand has to be thoroughly dry to jiggle into the joints. Don’t try to save money on a tamper rental by skipping this step. The last tamping will vibrate the sand into the joints, locking all the bricks together.
Step 15: Run the plate compactor on top of the pavers
Run the plate compactor on top of the pavers. Pass over the patio four times, switching direction after each pass. Compact around the outer edge after each pass.
This type of patio and wall requires little to no maintenance. Don’t let dirt build up on them or you’ll provide a home for weeds, and be sure to wash the patio down periodically. Sealers are available for enhancing the paver color, but once you apply them, you need to repeat the process every few years.