Step 4: Working in sections about one metre long at a time, trowel in a 2.5-centimetre base of aggregate such as fine limestone screenings for the concrete bricks to sit on. A deeper base isn’t necessary, as it doesn’t get heavy foot or vehicular traffic; any bricks that shift out of alignment over time can easily be reset. Alternatively, sand can be used, but it shifts around, while screenings lock together.
Step 5: Smooth out the screenings with a board. Then place the board over a section and firmly tamp it several times with one of the bricks, gradually moving the board along the trench, tamping as you go and checking periodically with a spirit level. The aim is to make a level, firm foundation. Sprinkle an additional handful of screenings on top of the base to provide a bit of “give” when setting in the bricks.
Step 6: Starting at one end, begin positioning the concrete bricks, aligning the front edge with the string (if using) and checking to make sure the top sits level with the soil on the turf side. Place the next two or three, keeping their edges as close to each other as possible. Place a board flat across the top and tamp them down. Recheck the positioning before moving on.
Hint: Placing the first four or five concrete bricks can be frustrating. They may not sit evenly, or they may tip forward or backwards. Be prepared to make several minute adjustments in the base to get them aligned. Be patient. Or find someone more patient than you (which is why you see my husband in these photos, not me). However, once the first dozen bricks are laid, you develop a rhythm and intuit when to add or subtract screenings to keep the bricks level and how hard to tamp. The rest of the installation goes more quickly.
Step 7: If your mowing strip follows a slope, as ours does, use a spirit level to periodically check that the bricks are descending or ascending evenly.
Finishing touch: Fill in the gaps between the front edge of the mowing strip and the turf with fine topsoil. Taper the soil at the front of the flower bed down to where it meets the back edge of the mowing strip.