Building A Concrete Retaining Wall Building A Concrete Retaining Wall

What You'll Need
Concrete blocks
Capstones
Paver or sand base
Masonry adhesive
String line and level
Spirit level
Flat nose shovel
Garden trowel
Hand tamper
Circular saw with masonry blade or mason's chisel and sledgehammer
Ear and eye protection, particle mask
Hose or watering can

A concrete retaining wall can improve drainage, level a badly sloping yard and give your house real presence. 

Step 1 - Plan

Lay out a hose.  Remember you're working with blocks that are 9 to 12 inches across, so your best options are a straight or gently curved line.

Measure the length of your planned wall, including curves, corners, etc. Don't try to go any higher than 3 feet—in most municipalities, anything taller will require an engineer's participation.

Do the math:

  • Length of wall divided by length of blocks equals blocks needed for first row or course.
  • Height of wall divided by height of block equals number of courses. 
  • Multiply these 2 numbers to get the minimum number of blocks to buy.

To finish off the top, get one course's length of wall caps. Plan in several extras of each. Keep the receipt and return unused blocks later.

Mark your final placement with string and stakes. This marks the front bottom edge of your wall. If you are making your wall directly behind your front sidewalk, check the straightness of the sidewalk edge and work off that.

Step 2 - Dig

Using your string line as a guide, dig a trench that's at least half the height of your blocks plus 1 inch. If your blocks are 6 inches high, your trench will be 4 inches deep.

If the ground isn't level, dig deeper at the higher end. In extreme cases you may even end up burying some blocks below ground level as the slope rises. The wall should be level with the horizon, not follow the slope of the ground.

Level the bottom of the trench. Get down on your knees with a trowel if necessary. Tamp it down, water it well and let it dry to settle the soil.

Add a 1-inch layer of paver or sand base. Wet it down and tamp it to form a rigid foundation.

Step 3 - Build

Lay blocks in the trench, putting cut blocks in less obtrusive places. Most of your leveling work has already been done, but keep leveling the blocks with the horizon and with each other, using soil or paver base to fix low spots. If you're working with a curve, the wedged shape of the blocks will help you—just make sure the vertical edges of the blocks snug up to each other. When you're done with the first course, backfill soil behind the blocks.

To cut a block, use a circular saw (or masonry chisel, which requires more strength). The blade won't saw completely through: make one pass, flip the block and cut again. This may take practice. Secure partial blocks to the previous row, if any, with adhesive.

The 'lip' on the block's bottom automatically gives the wall the right step-back. Lay the second course so that the block straddles two in the first course. You may have to knock some of the lip off to make the block sit right around curves, but try to keep most of it intact.

Lay the other courses, occasionally checking level and backfilling as you go.

For the top course, lay the capstones end to end, cutting edges to different angles when necessary. Fasten them to the top of the wall with adhesive.

Finish backfilling, adding extra topsoil if needed.

Step 4 - Finish Up

If you wish, plant ground cover or a floral border behind the wall. If you're building adjacent to a sidewalk, you can fill crevices with paver base or even little plants.

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