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Build a Block Retaining Wall

A block retaining wall might be just what your landscape needs if you want to level a steep slope or enclose an area for a decorative garden. With a little effort, you'll have a beautifully landscaped area that's easy to maintain.

Block Retaining Wall.

Building Retaining Walls

Interlocking Retaining Wall Block.

Interlocking concrete retaining blocks require no mortar. Aside from the weight, they're almost as easy to assemble as children's interlocking blocks. If you make mistakes or change your mind about the location or shape of your wall as you're building, just dismantle it and start over.

Since these systems use no mortar or rebar reinforcement system, they're more appropriate for terraces or raised beds with low walls than those with tall walls. A system of terraces creates a pleasant, stepped slope that's safer than a single, tall wall. A system of terraces also gives you many planting and landscaping opportunities and helps control erosion.

Caution

Check your local building codes or Home Owner's Association regulations before installing a retaining wall.

How Interlocking Retaining Wall Block Systems Work

Interlocking retaining wall blocks in mortarless systems have a lip on the bottom of the rear side to lock the blocks together. Filling the cavity behind the wall pushes the blocks forward, strengthening the joints between the lips and the underlying blocks. The blocks taper from the front face to the rear to allow easy formation of curves.

Mortarless wall block is intended for construction of relatively low walls. Maximum dry-fit heights vary by product, but for general reference consider a maximum of 15 to 28 inches as a guide for planning purposes.

Tips for Your Retaining Wall Project

  • When figuring how many blocks you'll need for your wall, remember that curves require more blocks than straight runs.
  • When you take delivery of the blocks, don't have the pallets placed on your driveway. They're extremely heavy and could damage your pavement.
Caution

Follow the block manufacturer's instructions concerning height limits.

Dig the Trench for Your Retaining Wall

The key to successful retaining wall construction is a level foundation of blocks. Your wall will be much easier to build if you start with a level base and level each additional course as you go. The foundation course must be partially below ground level so that the soil holds it firmly in place.

If your property slopes, you may have to dig your foundation trench in a series of steps equal to the height of the blocks. Then, as you continue with construction, build up the lower sections with block until the stepped areas accept successive courses of blocks in a level and seamless wall.

Step 1

Measure out your prospective wall using stakes and string to mark off the key points or using a garden hose to mark off its perimeter.

Caution

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

Step 2

Digging Trench.

Dig a trench for the foundation course. The dimensions of the trench will vary depending on the size of your block, but it will generally be about four to six inches deep. The width of the trench should be twice the front-to-back measurement of your blocks. Remember, the foundation course should be partially below ground level.

Step 3

Tamp the trench with a hand tamper to compact the underlying soil.

Step 4

Add a 2-inch to 3-inch layer of paver base. Rake the layer to create a level surface and tamp. This layer will allow you to level the blocks more easily and accurately.

Lay the Foundation Course of Your Retaining Wall

Once you have a sound foundation trench, you can begin laying your blocks. The base of your wall provides level support and the partially buried foundation course of block prevents the wall from moving. Both factors are crucial to the integrity and longevity of your wall.

Good to Know

Check for level front to back and side to side every few feet as you build each course.

Step 1

Removing the Rear Lip.

Use a chisel and hammer to remove the rear lip from the blocks that you will use for the foundation course.

Caution

Wear eye protection when using the chisel and hammer to remove the lip.

Step 2

Set the first block in place and check the level. If the block isn't level, add a small amount of paver base as needed and tap it with the rubber mallet or butt end of your hammer to adjust it.

Leveling provides strength and prevents the wall from tipping forward. It's a key factor to a long-lasting wall. If you leave the wall uneven at the base, the error will grow dramatically with each course. It's much easier to make the correction early on than to try to correct it later.

Step 3

Leveling the Course.

If your property is relatively flat, continue laying the foundation course, making sure that all blocks are level and partially below ground. If your property is not flat, use the stepped approach mentioned above.

Good to Know

Sweep off any debris from each course before you lay the next course.

Step 4

To prevent the soil from seeping through the spaces between the blocks, line the cavity behind the wall with porous landscape fabric. Start at the base of the cavity and unroll the fabric to a length that will overlap where the top course of block will be. Cut the fabric and continue along the length of the wall until you've lined the entire cavity.

Step 5

Fill the cavity, covering the landscape fabric with gravel to allow water to drain properly. Adding proper drainage prevents water pressure from building up behind the wall and causing it to collapse. All retaining walls encounter the force of water, whether it's from heavy rains or some other unforeseen event.

Caution

Keep gutter downspouts pointed away from your retaining wall.

Lay Additional Courses for Your Retaining Wall

Once you have a good, level foundation course, you can begin laying the remaining courses.

Step 1

Cut one block in half for the start of the second course. This ensures that the first and second courses are staggered. For information on cutting blocks see Cut Patio Blocks.

Caution

Wear eye protection when cutting block. If you use a power saw, you'll also need hearing protection and a dust mask.

Step 2

Set the rest of the second-course blocks in place, finishing with the remaining half of the block you cut. Make sure the blocks are level as you go. Correct any areas that are not level before adding additional courses.

Step 3

Pouring Gravel.

Fill the cavity behind the block and landscape fabric with more gravel as you lay each course and compact the gravel with the tamper. Keep the landscape fabric between the block and the gravel.

Step 4

Continue placing the blocks, staggering each course over the previous one, filling the cavity with gravel and tamping the gravel as you go.

Finishing Your Retaining Wall

Step 1

Securing Caps with Adhesive.

When you're ready to lay the final course of blocks or block caps, sweep off any debris from the previous course and secure the final course of blocks or wall caps to your wall with construction adhesive.

Step 2

Fold any excess landscape fabric over the gravel and cover with sod, topsoil or mulch.