When Carolyn Prentiss and her husband Craig Shaw decided to build raised beds around their Ashland home, the cost of materials almost quashed the project. Instead, the couple decided to complete their plan using broken concrete. That is usually a “rough” look, concedes Carolyn, but not this time. They hired Koeby Johnson, an Ashland stone mason who treated the concrete as if it were stone.
Number one, that meant being particular about the concrete the couple collected for the project. Number two was using traditional masonry techniques to fit the pieces together. The result is a handsome addition to their Craftsman-style home. “He even had masons stop and congratulate him while he was working,” says Carolyn, who is very happy with the results.
“I see it used and it looks nice. It lends itself to a more natural landscape,” says Medford landscape architect Bonnie Bayard. “It’s great for do-it-yourselfers. Because it’s recycled, it’s an available resource that’s not going to cost a lot.”
Bayard and a host of volunteers used the material to build beds in the compost demonstration garden in Bear Creek Park. Even though much of that site was built by amateurs and had been subject to lots of use, most of the low walls are intact. “It’s a much nicer wall when you use tools to refine the rock shape,” she concedes.
“It’s not that different than working with natural rock,” says Johnson. He broke larger slabs of concrete into bricks using “a big sledge hammer and brute force.” The bottom tier of a low wall (about 1 foot or less) can be placed directly on the soil. Higher walls should be placed on a footing. Bayard suggests crushed rock that has been tamped level. The lowest level is also the place to put any pieces with an uneven bottom. “Once you get that established, it really gets tricky,” says Johnson. “Then you want batches that were poured on level ground (so the bottom is level).”
Carolyn Prentiss gathered most of the concrete for her project by putting out a “Wanted: broken concrete” sign in front of her home. Watch out for “phantom dumpers,” says Bayard. “The quality of the concrete you use is very important. Try to match the color and width.” Johnson got even more creative. He once saw a truck loaded with the perfect concrete slabs while he was driving. He flagged that driver down, made a deal for the concrete and led him back to the work site.
When stacking pieces, place them so the break between them falls in a different place on each course. Fit the pieces together so the front is even and the sides fit tightly, says Johnson. The backside of these bricks will be covered with dirt, so evenness is not important. Where walls curve, masonry tools can smooth the block faces so they fit tightly and neatly, says Johnson.
“You want them as flush as possible so soil doesn’t spill out,” he says. “You want the tops to be even so you can build on them and they don’t move.”
Consult an engineer for retaining walls or any higher than 4 feet. It’s likely you will need to accommodate for drainage, especially if mortar is needed. Check building codes before you start.
If it works in your landscape, it’s a win/win situation. The concrete is put to work again, and stays out of the landfill. With the extra effort of tooling the concrete, it can even work in the front yard. Broken concrete; it just might do handsomely.