How to build with interlocking blocks

Written by mary lougee
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How to build with interlocking blocks
Build a retaining wall around a flower garden to hold the soil intact. (George Doyle/Stockbyte/Getty Images)

Interlocking blocks are made of concrete in many colours and sizes. The back of each block has a lip on it that sits over the block underneath it to interlock the two together. Interlocking blocks do not require mortar to bond each course together as bricks do, so you save valuable time in constructing a retaining wall or surrounding a flower bed. Retaining walls outline flower gardens and reduce soil erosion.

Skill level:

Things you need

  • Shovel
  • Tamper
  • String
  • 2 wooden stakes
  • Hammer
  • Level
  • Brick chisel

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  1. 1

    Dig a trench on the ground about half the depth of the interlocking blocks you are using and a few inches wider than the block's depth.

  2. 2

    Hammer a wooden stake on each end of the wall. Tamp the ground with a tamper on one end of the wall. Place one interlocking block in the tamped trench. Place a level on the block and level it both vertically and horizontally in the trench. Dig out additional soil if needed to level the block or fill in low spots with the soil out of the trench.

  3. 3

    Tie a piece of string onto the stake near the first block with the string at the same level as the top of the block. Tie the other end of string to the second stake at the same height from the ground. This will be a sight line for the first course of blocks to ensure they are level.

  4. 4

    Lay the rest of the first course of blocks butted up against each other on each side in the trench. Remove or add additional soil to level each block and tamp the ground down.

  5. 5

    Place one block on the ground. Place a brick chisel on one end of the centre line on the back of the block. Strike the chisel with a hammer to score the block. Move the chisel down the centre line next to the first score. Strike the chisel again to score the block. Continue moving the chisel and striking it to score the entire block. Pick the block up with one hand on each side of the score and rotate both hands down to break the block in half.

  6. 6

    Place one half-block on the first block of the first course from behind it and push it forward to interlock the lip on the half-block onto the block underneath. Place whole blocks next to the half block and continue interlocking them to the other end of the wall. Place a half-block on the end of the second course.

  7. 7

    Lay additional courses of blocks alternating starting with a full block and a half-block.

Tips and warnings

  • Building a wall with a full block on one course and a half-block to begin the next course alternates the butt joints of the blocks and gives the wall stability.
  • Buy curved blocks to make a circle or curved retaining wall. Place a garden hose on the ground to mark where you want the wall. Dig the trench and install the blocks in the same manner as a straight wall.
  • Interlocking blocks are stable without any mortar to hold the courses together up to a height of 4 feet.

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