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Retaining Wall Blocks Make This Job Easy
A retaining wall operates quite differently from other exterior walls. If you just want a wall to mark property lines or to keep in livestock, pets, or children, nothing is simpler than erecting a wall of cinderblocks or a wooden fence. True to its name, a retaining wall isn’t just there to look pretty; it’s in the business of retaining the soil packed behind it.
With this completely DIY-able project, the key ingredient is a material called a retaining wall block. There are four features that distinguish retaining wall blocks from other masonry items:
- Weight: One reason why these blocks are so good at keeping the soil at bay is their sheer weight. The biggest blocks weigh 61 pounds.
- Back Lip: A lip on the back side of the block helps you to position a block on top of the block below it.
- Backward Tilt: As the wall goes higher, it tilts backward. This has the same effect as a wrestler leaning forward to try to pin his opponent. Weight + tilt = retention.
- Angled Top: Looking at these blocks from the top, you will notice that they are angled. These angles help you create smooth inside and outside curves.
Materials and Tools Needed
- Retaining wall blocks
- Flat blade shovel
- Sand or gravel
- Bubble or laser level
- 2 to 4 inch long piece of 2 by 4 lumber
- Masonry or old Chisel
- 6-pound sledgehammer or framing hammer
- Safety glasses
Prepare Site for Blocks by Flattening and Levelling Ground
With your flat blade shovel, grade the soil where the blocks will rest until the soil is flat, level, and compact.
Use your short 2 by 4 as a screed to further level the soil by drawing the 2 by 4 towards you, scraping off soil to create a level area.
Lay Sand or Gravel as Base for Retaining Wall
There are various, often conflicting prescriptions for how much or little sand or gravel to lay down as a base for the wall.
Keep in mind that you want to provide a base that will keep your lowest course of blocks above any mud. Water will inevitably seep to the bottom of your wall, and when it collects at the base, it will turn into mud. By laying one or two inches of sand or gravel, you raise the lowest row above this mud.
Lay First Block of Retaining Wall
Begin one end of your wall with a single block. Press it firmly down into the base, though not so hard that you squeeze your base layer away.
Use your level to check this first block for the level in both directions: side to side and front to back.
Maintain Level of Each Block and Between Blocks
Lay down your next adjoining block.
This block must be perfectly level both on its own and in conjunction with the adjoining block. Use your bubble or laser level to span from one block to the next. Adjust the second block until it is perfectly in line with the first block.
Aligning block-to-block is highly important. As you continue to add courses of blocks upward, any differences between lower blocks will be transmitted to upper courses, often in disastrous ways.
Lay Block in Staggered Fashion for Stability
Do not lay blocks on top of each other in a column. While you can get by doing this with the very heavy (61-pound) blocks up to three rows high, this method will not work for lighter blocks.
To lay blocks in brickwork fashion, advance each upper row horizontally one-half block over (to cover those open half-block ends via cutting blocks will be shown later).
Brickwork masonry is enormously more stable than independent vertical columns.
Check Level With Each Course
Every row must be level. Keep spot-checking your level with the bubble or laser level.
The only way to keep an entire row at true level is to run a string between two posts pounded into the ground at either end of the wall. For posts, use spare plumbing pipe, 1 by 1’s with the ends cut into points, or rebar.
Prepare to Cut Block by Setting Chisel in Groove
To cut a retaining wall block in half, set the block on end, with the back side facing up. You will notice a V-notch groove in the back of the block.
Put on your safety glasses. Set your chisel into the block.
Cut Retaining Wall Block by Cleaving
With the 6-pound sledgehammer (holding near the head) or the framing hammer, sharply strike the end of the chisel until the block cleaves in half. You may need to strike several times for the block to break.
Set Half-Block at End of Row
Use one of the cut half-blocks to cover the end of the row.
Check Room for Back Side of Retaining Wall
When laying out your retaining wall, provide ample room between the lowest course of blocks and the soil behind it. Remember that as the blocks progress upward, they will tilt backward so you will need to cut back more of the hill than you might initially think.
Pictured here is a good example of the space behind the retaining wall. Note how the blocks are tilting backward, and how at least four feet of space has been provided for the backfill.
Backfill Retaining Wall Blocks With Sand or Gravel
Carefully fill the back side of the retaining wall with sand or gravel; this process is called backfilling.
Mete out the backfill material in small amounts in order to let the material settle. If you shovel too much at once, you may create hollow spaces in the backfill that can compromise the wall’s stability.
Occasionally jiggle the wall front-to-back in order to coax the backfill material into settling. The more compact the backfill, the more stable your wall will be over the long term.
By Lee Wallender