Retaining Wall Building Tips

Here is a quick guide to building a simple interlocking block retaining wall.

• Prepare and check council regulations
• Before you start, check with your local Council to see if building approval or engineering certification is required. In general, walls closer than 1.5m to a building, over 1 metre high or on a steep slope, may require building approval and certification by an engineer.
• Measure and calculate blocks
• Work out how many blocks you’ll need by measuring the length and height of your planned retaining wall. Add 5% for breakages and cuts.
• Dig & prepare the base
• Lay out where you are going to build the retaining wall by running a string line between two stakes, then dig a shallow trench approximately 180mm deep and 350mm wide. Fill with road base or coarse sand, compacting and levelling as you go.
• Lay the wall, creating drainage as you go
• Lay your first row using a rubber mallet top tap blocks into place. Ensure the first row is level with a spirit level.
• Place drainage material, such as gravel or blue metal, about 150mm wide behind your first row.
• Fill the cores and openings in the top of the blocks and between each block.
• For interlocking rows, use a masonry saw to cut a block to finish your first row and/or to start the second row to stagger the joints. 
• When you have completed two rows, add drainage. Lay slotted agricultural pipe on the gravel behind the blocks. Keep one end of the pipe clear – draining to a clear area or a drain – so that the ground water can escape.
• Continue laying blocks and drainage material. Make sure you compact backfill for each block height.
• Apply construction adhesive to the last row of blocks to secure in place. This can be on top of the blocks if you’re using capping blocks – or between the second to last and last rows.
• For maximum protection the retaining wall can be sealed after installation. Check recommendations from the manufacturer.
• Sweep with a stiff bristled broom to remove debris from the retaining wall.