If you want to build a concrete retaining wall with blocks, there are some steps you must take.

First, before starting your concrete retaining wall, call your utility company and ask to have the location of underground pipes and wires marked. They'll usually do this for free, and it will save you the incredibly big and costly hassle of unintentionally damaging utility lines.

Check your local building codes to find out whether the size concrete retaining wall you want to build requires a building permit. If so, you'll need to take care of this step before getting started.

If you are installing your retaining wall next to a sidewalk or deck, you may have to add a rail to comply with codes.

Planning and Preparation

If you're putting up a 4-ft. wall, you need to dig a trench that's deep enough to hold 4 to 6 inches of compacted base, an inch of leveling sand, and one-half the height of the first course of blocks.

Each subsequent course of concrete blocks should sit back by 0.75 inches with vertical overlaps of at least 4 inches. Each row should be secured to the next with pins.

Use crushed rock to backfill until the very top. On top, use a 6 inch deep cap of native soil to keep the surface water from entering the trench that's filled with rocks.

Use concrete adhesive to secure the cap blocks in place.

It would be hard to overemphasize the absolute necessity to begin your concrete retaining wall with a solid, level, compacted base. Otherwise your wall will be weak and look lumpy.

These instructions here are for a theoretical concrete block wall of 4 feet high or under.

For retaining walls higher than 4 feet, concrete block manufacturers require extra engineering and installation procedures such as using special reinforcement fabric.

The compactable base material is made up of different sized rock and sand particles. These interlock and compact to make a solid base. It is the same stuff that goes beneath road beds and concrete patios. It isn't the same stuff as the crushed gravel used for backfill.

Dig the Trench

Dig to a depth just below the frost line for your region and make it wide enough for the wall plus space to work.

Build the Forms

Brush the plywood with motor oil so that they will be easier to remove.

Nail studs of 2 x 4 lumber to the plywood, spaced 24 inches apart.

Assemble the form using end pieces of plywood and interior 2 x 4 spreaders.

Put the form in place and make certain that it is both level and plumb.

Brace it with outriggers (projecting beams that support the form) and stakes. If you don't have a helper, push the form into place with your foot and drive the stakes in.

Add Reinforcement

Using wire, tie horizontal rebar to the vertical rebar every 18 inches.

If you are planning to cap the wall with concrete. the vertical rods should protrude at least an inch or so beyond the bottom edges of the spreaders.

Infill Blocks With Concrete

While you can mix it in a wheelbarrow, it may be worth your while to rent a small concrete mixer. If you use a wheelbarrow, make a temporary ramp to the top of the form.

Make sure that your first row of blocks is absolutely level. Errors will propagate with each succeeding row of blocks.

The pouring phase will go much better if you have blocks, compactable base, backfill gravel and sand delivered.

While these raw materials may cost more from a specialty landscaping store than from a DIY supercenter, the smaller stores are often better able to deliver small batches of materials than the mega-stores are.

Get your helper to tamp down the concrete as you pour to get air bubbles out.

After the concrete has had a chance to set, smooth the surface with a wood float.

Let It Be... Let It Cure

After letting the wall cure properly for several days, you can remove the forms and install perforated drainpipe and the backfill.

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