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How to build an interlocking block retaining wall

Do you have a sloping block? Would you like a level area for the kids to play? How about a new entertaining area or garden bed surround?

A retaining wall could make all the difference.

Most low interlocking block retaining walls can be built by a confident DIYer.

It’s not that hard. Preparation is the key and maybe another set of hands on the day.

This is a step-by-step guide to building a simple interlocking block retaining wall.

Remember, if you have any more questions you can ask one of the expert associates in your local Masters Home Improvement store.

Before you start

Before building any type of retaining wall it is best to check with your local Council.  

Each Council is different and may require building approval or engineering certification.

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.

Calculate how many blocks you’ll need by measuring the length and height of your planned retaining wall. Add 5% for breakages and cuts.

The expert team at Masters can help you with how many blocks you’ll need and show you the different styles and colours available.

Be sure where you’re putting the wall

Lay out where you are going to build it. Run a string line between two stakes as a guide for building your retaining wall.

Dig a shallow trench approximately 180mm deep and 350mm wide. Remove any roots and soft earth.

This will also give you a good idea of how much flat space you’ll get when the wall is completed.

Fill the trench with road base or coarse sand. The easiest way to compact it is with a mechanical plate compacter. Make sure it’s level and continue until you have a 100mm levelling pad.

Lay your first row.

You can lay these dry – as the weight of the blocks should keep the wall in place. For added security, you can add some spots of cement or construction adhesive between blocks.

It’s crucial the first row of blocks is level. Otherwise the whole wall will be uneven.

Check and recheck with a spirit level. Use a rubber mallet to tap the blocks into position.

Make sure it will stay well drained

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.

If you need a partial block to complete a row, use a masonry saw. Be sure to wear eye, ear, and dust protection.

Ensure that you read the operating manuals of all equipment, such as plate compactors and masonry saws, and always wear the appropriate safety gear recommended by the manufacturer.

If you don’t need to cut a block to finish your first row, you'll need to cut one 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. 

Stand back and enjoy your handiwork.

Important - Please read: All information and tips in this publication are of a general nature only and Masters does not warrant the accuracy or completeness of the information and tips in this publication.  This publication is not intended to be a substitute for expert advice.  Masters advises you to always consult an experienced and qualified person when undertaking jobs of this kind (including consulting a qualified tradesperson such as an electrician or plumber where relevant expert services are required).  You should also consider any safety precautions that may be necessary when undertaking the work described in this publication (including wearing any necessary safety equipment such as safety glasses, goggles or ear protectors or hard hats).  The information and tips in this publication are provided on the basis that Masters excludes all liability for any loss or damage which is suffered or incurred (including, but not limited to, indirect and consequential loss or damage and whether or not such loss or damage could have been foreseen) for any personal injury or damage to property whatsoever resulting from the use of the information and tips in this publication.  Masters also notes that there may be laws, regulations or by-laws with which you must comply when undertaking the work described in this publication.  You should obtain all necessary permissions and permits from council and/or any other relevant statutory body or authority before carrying out any work.  Masters Home Improvement Australia Pty Ltd ABN 21 066 891 307.

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