In this how-to video, TOH Senior Technical Editor Mark Powers shows how to make a concrete block garden border that doubles as extra backyard seating.
Steps:
1. Lay out the width and shape of the wall. Place a stone at each end of the run, then drive a stake at least 1 inch around the sides of the stone to mark the width of the trench.
2. Tie a level mason’s line between the stakes—to use as a measuring guide when digging the trench. Hook the string in a notch on each stake to make it easier to move the line out of the way as you dig.
3. Dig until you get past the dark topsoil and reach the lighter subsoil, but no less than 6 inches. Measure off the mason’s line to keep the bottom of the trench level. If your ground slopes at all, the trench will be deeper at some points than others.
4. Line the trench with paver base—a mix of crushed stone and stone dust. Tamp it down in 3-inch layers.
5. Fill the trench until the shallowest part of it is still deep enough to fit half the height of one block plus one inch.
6. Spread an inch of stone dust over the paver base.
7. Set the first stone at the shallowest point A low stone wall can clearly mark your garden’s border while giving you extra places to sit. Using cast concrete blocks can reduce both the time to build one and the cost of materials. This Old House Senior Technical Editor Mark Powers demonstrates how to use them.
Planning Your Concrete Sitting Wall
Sitting walls are best placed around areas you already gather naturally. Consider the proximity to your patio and living area, views from the seats, amount of sun an area gets, and interesting landscape features are nearby.
Next, figure out the wall’s dimensions. Generally, sitting walls should be 18 to 24 inches high for comfortable seating, 12 to 18 inches wide for the cap stones, and as long as necessary to fit your desired seating capacity.
Marking and Digging for the Concrete Sitting Wall
Once you’ve settled on a location and size, you’ll need to do more planning to finalize the wall’s layout. Next, you’ll excavate the area to prepare for the foundation.
Marking the Layout
Lay out the wall’s width and shape. Place a stone at each end of the run, then drive a stake at least 1 inch around the sides of the stone to mark the width of the trench. You’ll backfill the extra space later.
Next, tie a level mason’s line between the stakes to use as a digging guide. To make digging easier, hook the string in a notch on each stake.
Excavating the Trench
Now, it’s time to dig the trench. Excavate until you reach the lighter subsoil—no less than 6 inches deep. Pay attention to your mason’s line to make sure the trench bottom stays level. If you’re building on sloping ground, the trench must be deeper in some areas to keep the base level.
Building the Concrete Sitting Wall Foundation
A strong foundation will help your sitting wall last for years. You’ll need to add some base material before placing the first layer of blocks.
Installing the Base Material
Line the trench with paver base, a mixture of crushed stone and stone dust. Tamp it down in a 3-inch layer.
Keep pouring and tamping until the shallowest part is deep enough to fit half the height of one block plus one inch. At this point, spread an extra layer of stone dust.
Laying the First Course
Set the first concrete block at the shallowest point of the trench. Make sure it’s level in all directions: side to side, front to back, and corner to corner. Once it’s level, tap it into place with a rubber mallet.
Keep laying the first course of blocks, butting them against each other and dropping them straight down. This will help you avoid dragging stone dust into the joints. Check each block for level and adjust as needed.
Once the first course of blocks is down, backfill the extra space around the outside with stone dust and dirt. This will keep the blocks from tilting as the soil settles.
Building the Concrete Sitting Wall
Once you have a steady first layer built, it’s time to add more layers until the wall reaches your desired height. You’ll cap it off with a special layer for seating.
Staggering the Joints
Stagger the joints between courses and start the second layer with a half block to create a stronger wall structure.
Score a block down the middle with a mason’s chisel to create a thin channel. Then, split the block along the score line and clean the edges with a brick hammer.
Laying Subsequent Courses
Apply a bead of masonry construction adhesive along the top of the first course. Then, lay the second course of blocks so they’re level and properly aligned.
As you lay the remaining courses, keep staggering joints and glue every other layer for added stability.
Capping the Wall
The last step is adding the capstones where you’ll sit. Turn the cap blocks perpendicular to the wall for a wider seating surface. Once they’re level and evenly spaced along the wall, secure them in place with masonry adhesive.
Building a Concrete Sitting Wall: Finishing Touches
Let the adhesive cure before you use the sitting wall. It typically takes about 24 hours for the compounds to reach their full strength.
For decorative finishing touches, consider planting low-growing flowers and shrubs along the base, adding mulch or decorative stones nearby, or highlighting the wall with landscape lighting. You can also place outdoor cushions or built-in planters on top of the wall.