A block retaining wall can add beauty to a yard while providing a practical function. The retaining wall can push a hill back, creating a level space for a patio, walkway, swing set, or an accessible mowing area. An attractive block retaining wall can also add value to a home.
Retaining wall blocks for a do-it-yourself project are commonly purchased at a local hardware store, such as Lowe’s or Home Depot. These blocks are generally 12" long x 7" deep x 4" high and have a lip along the bottom, back edge to lock rows together. The blocks are installed with the lip down so that the lip of the upper row pushes against the back edge of the lower row. This style of retaining wall block is recommended for a retaining wall up to three rows high and a cap block. A higher retaining wall may require a professional grade block that locks blocks together with steel rods. The do-it-yourself retaining wall block is also tapered toward the back. This feature allows for a rounded retaining wall design that contours with the landscape.
Retaining wall block for the do-it-yourself homeowner have two basic varieties, ‘Castle Wall’ and ‘Chisel Wall’. Castle wall blocks have an old fashioned appeal. A castle wall block has a rough face that can crumble, leaving small pebbles at the base of the wall. Chisel wall blocks have smooth chisel like face. Both varieties come in different colors and are made of concrete. A chisel wall block is more expensive than a castle wall block. I have learned that retaining wall blocks can be drastically marked down in the off season. It is a good idea to make sure to purchase enough blocks to complete the project, colors may vary from season to season.
The do-it-yourself homeowner should plan the retaining wall before the construction starts. Building a retaining wall at the base of a hill will require extra dirt to back fill behind the wall, while digging part of the bank will provide dirt that can be used to fill in behind the wall. Digging is the hardest part of the project.
The key to building a reliable block retaining wall is to start with a solid foundation. If the retaining wall is to be constructed on loose earth, a paver base foundation will provide a solid base. However, if the earth is already compact and solid then a paver base may not be necessary. A solid foundation will prevent settling, which will keep the retaining wall from sagging.
The first row of block is the most important. The first row sets the stage for how well the rest of the wall will fall into place. It is better to start the retaining wall at the lowest section of the wall, if possible, even if it is in the middle of the wall. It is easier to construct stepping up rather than stepping down, although this is not a requirement.
Leveling sand is used to level the first row. I use a 6-inch level to make sure the block is level across the block width and depth. I use a 36-inch level to make sure the wall remains level across the span of several blocks. A 36-inch level placed on the back surface can also ensure the blocks are placed in a straight line. A string line can also be used to establish a straight line. The vertical edge at the face of the block should be aligned with the adjacent block. This makes sure there are no gaps between blocks.
After I finish with the first row, I like to fill the "V" gap between blocks and directly behind the wall with rock (a "V" shape is created form the taper in opposite directions between blocks) I generally use rocks that were found in the yard or while digging. Gravel works as well. The rocks create a filter that helps prevent dirt from seeping out of the wall, while also creating a drain area for water behind the wall.
The second row may need to start with a half block to stagger joint lines. The stagger will make the wall stronger. Castle wall block generally have a score line molded into the block. Tapping the score line with a brick hammer will break the block in half. Chisel wall block do not have a score line and may require a saw or other means to cut the block in half. The block should sit flat on top of the first row. I like to check the block with a level to make sure the block has been correctly installed. Just like the first row, I like to fill the "V" gap between blocks and directly behind the wall with rock. I will also back fill behind the wall with dirt and pack the dirt.
The third row is constructed the same as the second row.
The last row that is installed is the "Cap Block". Cap block are rectangular in shape (or trapezoid if castle wall variety) and wider than regular block. A straight wall section will contain no gaps between the blocks. Pieces will need to be cut to fill in for outward curves and angles cut in the cap block for inward curves. The top row should be solid when completed. Cap block can be held in place with adhesive.
The finished block retaining wall will divide the hill into two separate and distinct contours. The base of the retaining wall can be a level area, while creating a more gentle slope to the area at the top of the retaining wall. I use the term "level" at the base of the wall as a generic term. There should be a gentle slope to allow rainwater to drain. This prevents mud puddles.
I am not a professional landscaper. This article is intended to convey my personal experiences with constructing simple block retaining walls around my home.