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How to Build a Retaining Wall

Give your plain landscape a stunning makeover with a block retaining wall.

Planning the Retaining Wall

Flange on the Back of a Retaining Wall Block.

The blocks for this project have a locking flange — which makes the installation easy. The interlocking blocks can be used to build walls up to 28 inches high. Follow the block manufacturer's instructions concerning wall height limits.

Plan your layout. Avoid having downspouts pointed at the retaining wall and, if it's against the house, keep soil and mulch well below the siding.

Your retaining wall design will determine how you mark the area. To mark a freeform layout, use a rope or hose to outline the shape. Then use a shovel to mark the outline. For straight lines, mark the entire bed area with stakes, string and marking paint. Mark curved corners by tying a string to a stake that's equidistant to the edge — creating a compass — and spraying the curves with marking paint.

To determine how many blocks you'll need per row, divide the total length of the wall by the length of the block. To see how many rows you'll need, divide the ideal wall height by the height of the block — account for the first row to be half-buried. See Planning for a Block Retaining Wall for more information on estimating project materials.

Before you buy materials or begin work, check local building codes and your homeowner's association regulations to see if there are any restrictions or requirements you need to follow. A permit may be mandatory in some areas.

Good to Know

Blocks can be heavy - wear a back brace if necessary. You may want to enlist a helper to share the work.  Consider having the material delivered.

Good to Know

Purchase 10% more blocks than your estimate. The excess should account for breakage, cutting blocks and replacements for future repairs.

Instructions

Preparing the Foundation

Step 1

Dig the Trench.

With the layout marked, you can begin digging the trench. To bury the first row about halfway, dig the trench about 4 to 6 inches deep and 12 inches wide, or twice the width of the block.

Caution

Before beginning any excavation, check for underground utilities. Call the North American One Call Referral Service at 1-888-258-0808 (or just dial 811) for a national directory of utility companies.

Step 2

Step the Trench on a Slope.

If the trench slopes, you'll have to step up or down to keep the blocks level. Use a torpedo level to create steps so that each section of the wall remains level. You do not want the wall to run parallel to the slope.

Step 3

Tamp Down the Dirt.

Tamp down the dirt with a hand tamper and keep it level.

Step 4

Rake the Paver Base.

Fill the trench with about 3 inches of paver base, spread it with a rake, and tamp it down. Tamping the base provides a strong foundation. When it's all level, you can begin installing the blocks.

Good to Know

Wet the paver base if it's dry and dusty.

Building the Retaining Wall

Step 1

Knock off the Flange.

For row one, knock off the flanges with a hammer and chisel so the blocks will sit flat.

Caution

Wear safety glasses and work gloves when using a chisel on the blocks.

Step 2

Check the First Block for Level.

Beginning at the end with the lowest elevation, set the first block in place and check for level side-to-side and front-to-back.

Step 3

Check for Level as You Install the Blocks.

Place the next block, making sure it's even with the first. Continue installing the first row, periodically checking for level.

Good to Know

A 6- to 9-inch torpedo level is useful for checking level of individual blocks or checking level front to back. A longer carpenter's or mason's level  — 24 inches and up — is good for checking level over several blocks.

Step 4

Fill Under the Block.

To level the rows and keep the blocks even, fill in under low blocks with paver base or tap down high blocks with a rubber mallet.

Step 5

Brush Dirt off of the Blocks.

After installing each row, sweep dirt off the tops.

Step 6

Stagger the Joints.

To start the second row you’ll have to cut a block to stagger the joints. Mark it, and cut it with a masonry blade.

Caution

Wear safety glasses, hearing protection and a safety mask / respirator when cutting block. Follow the saw and blade manufacturers' instructions for use and safety.

Step 7

Mark the Block.

Put the cut block in place, keeping the flange tight against the first row. Check it for level.

Step 8

Place Landscape Fabric Behind the Blocks.

After installing the next few rows, you'll need to add drainage directly behind the blocks. Lay down landscape fabric behind the wall, leaving enough excess to reach the top of the blocks.

Step 9

Fill in Gravel Behind the Blocks.

Fill in directly behind the wall with gravel, then continue to build, by adding more rows.

Step 10

Apply Concrete Adhesive.

For the last two rows of full blocks, apply concrete adhesive to the wall block tops, then set the next row of blocks in place.

Good to Know

If you're adding block caps, apply adhesive to the top row of block before placing the caps.

Step 11

Fold the Landscape Fabric.

Fold the excess fabric back and fill in with soil and plants.