How to Build a Block Retaining Wall - 8 Basic Steps

Written by amelia allonsy
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Block retaining walls allow you to create level areas in your landscape while preventing erosion. They are often used to create terraces along the height of a slope and along patios, in which a clean, level surface is desired. Installing a block retaining wall is not as difficult as it may seem -- it requires just eight basic steps. The most important part of the project is providing a firm foundation to prevent the wall from sinking and crumbling. Concrete blocks are available in many decorative styles to blend with the landscape.

Skill level:

Things you need

  • Shovel
  • 4-foot level
  • Torpedo level
  • Tamper
  • Class V compactable base material
  • Sand
  • 1-by-4-inch screed board
  • Rubber mallet
  • Crushed gravel
  • Concrete adhesive
  • Cap blocks

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  1. 1

    Excavate the area for the wall, creating a trench that is 4 to 6 inches deep plus at least half the height of the block; allow at least 1 foot of clearance space behind the wall as well. Level the area and tamp the soil to create a firm, flat surface.

  2. 2

    Pour in 4 to 6 inches of Class V compactable base material, which is a mixture of different sized rocks and sand that compact well. Level the base material and compact it about 1 inch down with a tamper.

  3. 3

    Add 1 to 2-inches of sand to the trench and level it with a straight screed board, such as a 1-by-4-inch board. The distance remaining from the top of the sand bed to the grade level should be half the height of the blocks or greater.

  4. 4

    Lay the first course of blocks side-by-side in the sand and tap them into place with a rubber mallet. Level the course from side to side with a 4-foot level and from front to back with a torpedo level; add more sand under blocks to level out low spots.

  5. 5

    Fill in the space behind and in front of the front course with soil up to the grade level; pack the soil tight to anchor the wall. At this point, no more than half of the blocks should be visible above the soil.

  6. 6

    Continue laying the other courses on top of the previous course, allowing at least 4 inches of overlap for the vertical joints; the vertical joint created by two blocks is commonly lined up in the centre of the block above and below. Each course should be set back 3/4 inch farther into the slope than the course below.

  7. 7

    Backfill the area behind the blocks with crushed gravel to provide drainage between the soil in the slope and the block wall. Backfill to the height of one course before continuing with the next course.

  8. 8

    Apply concrete adhesive to the cap blocks and place them on top of the last course, perpendicular with the blocks in the wall. The cap blocks may set back from the wall, line up with the wall face or overhang slightly, depending on preference.

Tips and warnings

  • Some blocks may have holes for metal pins that drive in to lock the courses together.
  • You may add landscape fabric to the space behind the wall to prevent soil from mixing with the drainage gravel.
  • Retaining walls taller than 3 to 4 feet should be built by a professional contractor; this may be required by local building codes. To avoid hiring a contractor, you can build several short, terraced retaining walls to hold back a slope.

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