By Paul Bianchina
Installing retaining wall blocks is one of those projects made for the do-it-yourselfer. The installation techniques are easy to learn; the finished product is professional; and the sense of satisfaction at the end of the day is tremendous. And you get some good exercise thrown in for free!
Retaining wall blocks are made of lightweight cement and aggregate, and are most commonly seen as a solid block with smooth-angled sides, a flat top and bottom, and a rough, slightly rounded face. They are relatively new as building materials go, but have gained tremendous popularity in a very short time. Originally available in very limited shapes and sizes, and only in gray, you can now find variations from different manufacturers in several sizes, several shapes and a variety of colors. These include the traditional angle-sided blocks, straight-sided blocks, thin cap blocks that are used for finishing off the top of an installation, and even hollow blocks that allow plants and flowers to be planted inside. Besides the original gray, you can now find these blocks in tan, pink, brown and antique (basically a mixture of gray and pink).
As the name implies, retaining wall blocks are used to construct retaining walls of various heights and configurations. Most walls can be constructed simply by stacking the blocks up, while others that will be tall or have to restrain heavy loads may require special reinforcement.
Installation
A basic installation of retaining wall blocks begins with the excavation and preparation of a base. First, dig a shallow trench about 4 to 6 inches deep and a little wider than the depth of the block. Fill the trench with about 2 inches of base rock - typically ¾-minus crushed rock, available from most landscapers - then level and compact the rock to form a flat and solid base.
The first course of block is installed directly on the base rock, with no actual attachment other than their own weight. The blocks are laid side to side with the edges touching, and are leveled as they are set to ensure that the rest of the wall goes up evenly. The better the initial base of crushed rock is installed, the easier it will be to install the first course of block, but you can add or remove rock as needed to get the blocks level.
Subsequent courses are installed simply by stacking the blocks on top of the previous row. Row two should start off with a half block, so that the ends of the row two blocks meet over the center of each of the row one blocks. Row three starts off with a full block again, so that the butt joints of that row fall over the center of the blocks below. Continue to alternate the rows as you go up so the joints of one row are always over the center of the previous row.
Depending on the type of block you are using, there is typically some sort of key that locks one row to the row below it. In its simplest form, this may be a small lip on the bottom of the block that overlaps the top of the block below it. For higher walls with greater soil retention capabilities, there may be protrusions on the blocks that lock into slots on the other block, or there may even be overlapping holes into which fiberglass pins are inserted that lock the blocks together.
As the courses are installed, they are also backfilled for stability. Backfilling in the form of crushed rock or gravel is placed along the back of the blocks and compacted, and then soil is backfilled behind the rock as needed to complete the filling of the area behind the wall.
If needed, the blocks can be cut using a hammer and a brick chisel. The chisel is used to score the block along the desired cut line, then the rest of the block can be broken along the line using a hammer. If you have a lot of blocks to cut, or if it's important that the blocks are cut in clean lines or along precise angles, you might consider renting a water-cooled masonry saw from you local rental yard. With either cutting method, wear the appropriate protective clothing and eye protection, and follow all necessary safety precautions.
Retaining wall blocks are available from most home centers and masonry retailers, as well as some lumberyards and larger department and discount stores. Remember to pay close attention to the manufacturer's instructions for installation, and do not overload the capacity of the wall.
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