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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, as this video explains. With a little effort, you'll have a beautifully landscaped area that's easy to maintain. The finished product looks complicated, but the project is quite simple, requiring only basic tools.


Take Control of Your Yard with Retaining Walls

Take Control of Your Yard with Retaining Walls

These concrete retaining blocks interlock and 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, 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.


How Block Systems Work

Retaining wall blocks in mortarless systems have a lip on the bottom rear side to lock the blocks together and create a step effect. When the cavity behind the wall is filled with soil, the blocks are pushed forward, strengthening the joints between the lips and the underlying blocks. The blocks are tapered from the front face to the rear to allow easy formation of curves.

Mortarless wall block is intended for construction of relatively low walls. Taller walls can be constructed but further consideration must be given to drainage, reinforcement and stability. Recommended dry-fit heights vary by product but for general reference, consider 15 inches to 28 inches as a guide for planning purposes.

Consult the manufacturer's instructions concerning height limits or recommendations made by the manufacturer.

Helpful Tips for Your Retaining Wall Project
  • When figuring how many blocks you'll need for your wall, remember that they are basically 1 foot long. Also note that curves require more blocks than straight runs.
  • When the blocks are delivered, don't have the pallets placed on your driveway because they're extremely heavy and could cause damage to your pavement.
  • To accurately cut a block, score a line around it with a 3-1/2-inch brick chisel and a 3-pound sledgehammer. Place the cutting edge of the chisel in the center of the score line, and strike the chisel sharply with the sledgehammer. A circular saw with a masonry blade makes quick work of cutting – just make sure you use it safely.
  • After you dig the trench for the wall, use leveling sand or paver base as a foundation for the first course. The sand allows the blocks to be leveled more easily and accurately.
Wear eye protection when cutting block. If you use a masonry saw, you'll also need hearing protection and a dust mask.


Dig the Trench for Your Retaining Wall

The key to successful retaining wall construction is a level foundation of blocks. The foundation course must be at 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 use a garden hose to mark off its perimeter.


Step 2

Starting at the lowest point, use a flat-pointed shovel to dig a trench for the foundation course. The dimensions of the trench will vary depending on the size of your block — generally about 4 inches deep. The foundation course should be below-ground level.

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 3

Tamp the trench with a hand tamper to compact the underlying soil. Add a layer of leveling sand or paver base (1 to 2 inches) and tamp.



Lay the Courses of Your Retaining Wall

Lay the Courses of Your Retaining Wall

Once you have a sound foundation trench, you can begin laying your blocks. Regularly check for levelness as you build each course.


Step 1

Set the first block in place. Check the level. If the block isn't level, tap it with the rubber mallet or butt end of your hammer to adjust it.


Step 2

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


Step 3

After the entire foundation course is installed, set one block in position at each end of the foundation course. The lip of each block should fit against the back of the foundation course block. Use a pair of line blocks and a line level to make sure that the first and last blocks are level with each other. If they aren't, adjust the retaining wall blocks until the foundation course is completely level.


Step 4

Cut one block in half for the start of the second course. This ensures that the first and second courses are staggered. Set the rest of the second-course blocks in place, and then fill the trench around the foundation course with soil. Continue placing the blocks, making sure each course is staggered over the previous one.



Fill the Cavity

To prevent the soil from seeping through the spaces between the blocks, line the cavity behind the wall with porous landscape fabric.


Step 1

Start at the base of the cavity, and unroll the fabric until it overlaps the top course of block. Cut the fabric and continue along the length of the wall until the entire cavity is lined.


Step 2

Fill the cavity. If the wall is 2 1/2 feet or higher, fill the area closest to the block with gravel. You should place gravel to a width of about 6 inches from the block. Fill the rest of the cavity with soil to facilitate drainage.


Step 3

Trim the excess landscape fabric. Top off the terraces with decorative stone or mulch.

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