How to Build a Concrete Block Retaining Wall

Steps To Building A Retaining Wall With Concrete Blocks.

This article will serve as a step by step guide to what is involved in building a concrete block retaining wall in your garden, especially if you have a sloping block and wish to create usable level areas.

1. Contact Your Local Council

   If you are contemplating building a retaining wall that will be higher than 500mm in suburban Adelaide, South Australia, you’ll probably require council approval before you start. You may also have to supply an engineers inspection report detailing how you will be building the wall, taking into consideration water runoff and the type of soil you will be retaining; including any structures within a metre of the wall.

2. Locate Your Wall

   With a couple of garden stakes and string, mark out exactly where your garden wall will be located on your property. Make sure you have the line straight, parallel or perpendicular with existing walls is a good idea so that everything will look square.

3. Add 100mm Road base

   Dig out 100mm of soil where your wall blocks will be sitting and replace this with 100mm of road base. To achieve a good level of compaction, put down about 30mm before wetting with a garden hose and compacting with a heavy block; repeat 3 times.

4. Lay The Retaining Wall Blocks

   Start laying the concrete retaining wall blocks next to each other; with the front along your string line. Using a spirit level, make sure there is no tilt; either front to back or side to side. Take your time placing the blocks; especially on the first course because if you find the wall is uneven at the top, you’ll have to remove them all and start again.

5. Install Agricultural Drain

   Insert an agricultural drain about 100mm to 150mm behind the first course of retaining wall blocks before starting to backfill with blue metal gravel. The purpose of this is to keep as much water away from the block wall as possible.

6. Add Additional Courses

   Add the next row of blocks on top of the first, making sure that you are laying them in a half bond manner for extra strength; i.e. the vertical joints from the first course should be in the middle of the second course of blocks, looking like a brick wall. For extra strength you can fill the blocks with blue metal gravel as you stack them. Complete the required number of courses until you reach the top.

7. Add Capping blocks

   To finish the wall off, add your chosen capping block. This could be a bullnose shape or have a squarer end; it’s up to personal preference and availability. These capping pieces should be secured with landscape adhesive or a product such as liquid nails from your local hardware store.

8. Backfill

   You have been backfilling as you add extra courses with blue metal gravel. Once you reach the top, add a dish drain to direct surface water run off in about 100mm of organic compost mix soil. This will provide a good base if you will be growing lawn next to the top of the wall. Keep the backfill material lower than the top of your retaining block wall.