DIY expert Frank Gardner needed to find a simple system for installing a retaining wall in a just a day.
To start, establish the line of the wall, excavating 200mm behind it, then use a laser level or dumpy to set the finished height of the wall either end, setting out a stringline as a guide.
Calculating the materials
How to install a retaining wall
Excavate two 550mm deep holes for the end posts, pour in concrete to 600mm from the top, use a spirit level to check for plumb in both directions then check the post is the right height. TIP A 20kg bag of cement mixed with gravel and sand fills three holes.
Next, set up a stringline to use as a guide then position a base sleeper in each end post. Position the joiner posts then dig 550mm deep holes and concrete them into position using a spirit level to plumb, aligning them with the stringline and leaving to dry.
Position and concrete the corner posts, using a builder’s square to install the sleepers at 90° to the wall. TIP To build steps later we added a 1200mm deep and 2400mm wide recessed area, incorporating four corner posts.
Next, position the base sleepers, levelling and packing them to leave exactly 400mm of post above then install the middle and top rows. TIP Check the height of the top sleeper matches the post so the capping sits flush along the wall.
Position geotech filter cloth behind the wall and fold it over the sleepers. Install 20m of 100mm agflo pipe with clear exits at the ends then cover with 20mm gravel to 300mm deep, folding the cloth back to separate the drainage and backfill.
Next, square cut and mitre the capping, apply construction adhesive to the ends and secure to the sleepers with 75mm x 14g galvanised bugle screws then use a router with a roundover bit to remove splinters and trim the edges. Apply two coats of decking stain.
Follow the labelled diagram above to build the retaining wall. It has the name of all the parts and the measurements to help you cut the components and assemble the retaining wall.