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Until concrete retaining wall systems muscled their way onto the scene 20 years ago, there were few do-it-yourself-friendly materials to choose from. Rock and stone were labor intensive to gather (or expensive to buy) and tricky to install. Treated timbers, despite claims to the contrary, often rotted within 15 years. Railroad ties looked like, well, railroad ties, and other options, like poured concrete or mortared brick, were best left to the pros. But concrete retaining wall systems—easy to install, widely available, reasonably priced, long-lasting and offered in a wide selection of colors and patterns—changed all that.
A retaining wall can solve many problems. It can convert steep, hard-to-mow hills into terraced, usable planting beds. It can prevent erosion, help level a patio area, create tree borders, or simply add visual interest to a rolling yard.
Fig. A Anatomy Of A Retaining Wall
Click image to enlarge.
A retaining wall is only as straight and solid as the base it’s built on. For a 4-ft. tall wall, excavate a trench deep enough to accommodate 4 to 6 in. of compacted base, 1 in. of leveling sand and half the height of the first course of blocks. Step succeeding courses back 3/4 in., overlap vertical joints at least 4 in. and secure one row to the next with pins. Backfill with crushed rock, except for the top, where you should install a 6-in. “cap” of native soil to help keep surface water from entering the rock-filled trench. Use concrete adhesive to secure the cap blocks.
The Versa-Lok brand retaining wall system we installed uses nylon pins to align and secure horizontal rows of 80-lb. blocks. (You can reach Versa-Lok at www.versa-lok.com.) Other block systems use lips, gravity and filled cores to connect rows and increase strength. Your system may differ, but most of the preparation and installation steps remain the same. Here’s how to install your wall.
Lifesaving Tip
For safety’s sake, call your utility companies and have them mark the location of underground wires and pipes. The service is usually free—and you’ll avoid dangerous and costly surprises.
Don't Skimp On Time, Tools Or Materials
The wall we built was a weekend-long project, and an exhausting one at that. It took a day to rip out the old, collapsing retaining wall, to dig farther into the hill to provide room for the backfill gravel and to help unload materials. It took another day to install the base, blocks and backfill.
Before launching into this project, contact your local building code official. Depending on the height and location of your wall, there may be structural, drainage and setback (the distance from wall to property line) considerations. A permit may be required.
Timesaving Tip
Install that first row of blocks dead level. Otherwise, those dips and humps will haunt you with each succeeding course.
Unless you own a heavy-duty truck (and back!), have your blocks, compactable base, sand and backfill gravel delivered. Blocks may cost slightly more at specialty landscaping stores than at home centers, but landscaping stores are often better equipped to deliver the small batches of base, sand and gravel that you’ll need for installing the blocks.
We used a transit level to establish a flat base. But unless you own or rent one and know how to use it properly, just use a 4-ft. level taped to a long, straight 2x4, especially for short walls. The tamper, brick tongs and block chisel are available at rental yards.
Build Straight And Solid From Start To Finish
Every manufacturer and consultant we contacted stressed the absolute necessity of starting with a solid, level and well-compacted base. Failure to do this will result in a weak, wavy wall. Bear in mind:
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If your wall is higher than 4 ft., most concrete block manufacturers require extra engineering and installation steps not shown here. These steps range from using special reinforcement fabric to installing a series of terraces rather than one tall wall. Most manufacturers provide good printed installation guidelines. If you purchase your blocks from a specialty landscape center, there may be an onsite designer or engineer to help you.
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Before getting started, contact local utility companies to mark the location of underground wires and pipes. Telephone and cable TV wires are often buried just beneath the surface.
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In the Midwest, the compactable base material is often referred to as “Class V” (as in the Roman numeral for five). In other regions, the rock may vary and the material may go by a different name. The important quality of the material is its different-sized rock and sand particles that interlock and compact to create a solid base. It’s the same material used beneath road beds and paver patios. Make sure you use the right stuff. It’s NOT the same as the crushed gravel you use for backfill.
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The 16-in. wide x 12-in. deep x 6-in. high blocks we installed weigh 80 lbs. each. A brick tong doesn’t make them lighter, but it does make them less clumsy to handle, easier to position and less likely to crush fingers.
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If your wall borders a sidewalk or deck, you may need a code-compliant rail. Contact your local building code department.
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