Stone Slab Steps
Tips on Installing Them in the Landscape
A slope can be transformed into a showstopper by the addition of a few stone slab steps flanked on both sides by plants. Stone slab steps are my favorite kind of informal garden steps because they are durable, add interest to a garden and provide a little bit of adventure to those nimble enough to climb them. Stone slabs are large, flat rocks, fabricated in the quarry, that are relatively uniform in thickness, making it comfortable to walk on.
Note - you should add handrails for safety. These are not the kind of steps you use as an entry to a house or in any area where there is a lot of foot traffic. This is because they may be tricky in wet, snowy or icy conditions. However, stone slab steps are a wonderful hillside solution and make a great view from a house or deck.
You can find stone slabs at a local stone supply yard. They are fashioned from a wide variety of stone including bluestone, granite, sandstone, limestone and more. Choose slabs that are without cracks or unsightly gashes. Touch their surface to determine if they are suitably rough for adequate traction. Smooth surface slabs are dangerous to walk on in wet conditions.
Below is the process for installing slab steps.
1. Determine how many slabs you will need
In order ensure that you have enough stone slabs for your steps, determine the vertical rise of the slope. An easy way to find this out is to use a straight wooden board, a tape measure, and a carpenter's level. Lay the board horizontally out from the top of the slope and place the carpenter's level atop it. Once the board is level, use the tape measure to find the vertical distance from the ground up to the bottom of the board. Now measure the height of your stone slabs. Generally, individual outdoor steps feel comfortable when they are between 5" and 7" high. Divide the vertical height by the thickness of the slab. For example, if the rise measures 18 inches and your slabs are 6” high, you will need 3 slabs (18÷6=3).
2. Excavate the base of the first step and fill with crushed stone
The base of the steps are all-important. Like the song says, It’s All About the Base. The slab steps must sit on a deep, compacted base of crushed stone or gravel for stability – you do not want them to move or sink into the ground. Pick the slab that you want to use for your first step. Dig a 12” deep hole into the base of the slope that fits the first stone, stamp on the soil to make it firm and then place a large piece of woven geotextile fabric (often called filter fabric) in the bottom of the hole. Make it large enough to go up the sides of the hole. You can also use smaller pieces and overlap them. Filter fabric prevents the crushed stone from sinking into the soil beneath.
Now install a 10” deep layer of ¾” crushed stone. Fill the stone in 3” layers and tamp it down by placing a short piece of 2" x 4" lumber against the stone and hitting it firmly with a rubber mallet. Do this repeatedly on the entire surface until it is well compacted. Use a carpenter's level to make sure the crushed stone surface is close to level and pitched a little forward. Now you have a sturdy footing.
Top the crushed stone with a 2” layer of fine crushed stone such as item four (also known as quarry run). This makes a great setting bed. The bed should pitch ever so slightly forward (1/4” per foot) to promote drainage. The rainwater runs out, away from the steps. You don’t want rainwater to run backward into the hill because it might freeze there and heave the stone steps.
You can adjust the slab’s height by altering the depth of the setting bed to make it sit higher or lower. You can also hit the slab step with a mallet to settle it firmly.
3. Lay second step partially atop first step and continue
Now that your first step is in place, dig back into the hillside to fit the next step and repeat the process. This step sits partially atop the first slab and the rest of it will sit on a crushed stone base. You determine how much to overlap the first step but remember to leave at least 12- 14” inches for the step tread. The step can be deeper if you choose.
4. Soften the sides with plantings
The key to beautiful stone slab steps is to blend them into the landscape. Add good quality topsoil to the sides of the stones and plant with shrubs or interesting small plants such as yellow creeping Jenny, Japanese forest grass, native Carex (sedge), to name just a few. Or you can add some hefty rocks to hold back the sides of the steps. Rocks placed next to the steps help form a perfect planting area for displaying plants.
The Hand Tools You Need for Slab Steps:
Wheelbarrow
digging bar
Digging shovel
4-ft. carpenter’s level
tape measure
heavy-duty bow rake
2” x 4” piece of lumber
hand cart or tree dolly
rubber mallet
Machine or By Hand?
In order to build stone slab steps you may need heavy-duty equipment such as a mini-excavator or skid-steer. The machine operator uses chains or nylon straps to carry the slabs and set them gently into position. Use heavy metal ‘digging bars’ to maneuver slabs in place. Place plywood boards on the lawn as a temporary road for the machine.
Of course, if you choose smaller slabs, you may be able to move them with a hand-truck or tree dolly. I find a hand truck minimizes damage to the surrounding lawn and landscape. One tip: use a hand truck or tree dolly with big, fat pneumatic wheels so that they don’t leave ruts in the lawn. Or use plywood boards set on the lawn.
I hope you enjoyed this post!
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