When constructing retaining walls, interlocking block systems have become a go-to choice for builders, developers, and landscapers across Australia. These systems offer strength, simplicity, and speed,  making them suitable for everything from residential gardens to large-scale commercial developments.

In this guide, we’ll cover everything builders need to know when working with interlocking retaining wall blocks, from site preparation to installation tips and compliance considerations.

Interlocking retaining wall blocks are concrete units designed with a tongue-and-groove or lipped system that connects each block mechanically without mortar. This dry-stack method ensures:

• Faster installation
• Uniform alignment
• Enhanced stability through gravity and design

These systems are engineered to support substantial soil loads, making them suitable for both aesthetic and structural applications.

Explore  Austral Masonry’s retaining wall systems to see popular options like Heron, Hayman and Sydneystone.

• No mortar required: Speeds up the process and reduces labour complexity.
• Consistent appearance: Block dimensions are precisely manufactured.
• Scalable: Suitable for both low garden walls and engineered high-load solutions.
• DIY-compatible: Great for clients seeking cost-effective installation options.

They also allow for easy integration of curves, corners, and steps within a modular design.

Different systems are rated for different wall heights and loading conditions. 

Always:

• Check the manufacturer's product datasheets
• Refer to engineering guidelines for walls over 0.5m
• Confirm with local council if a building permit is required

Water pressure is one of the biggest causes of retaining wall failure. Depending on your engineers wall design you will need to plan for:

• Filter fabric behind the wall
• A drainage zone (20mm gravel)
• A sloped agi-pipe (with exit to daylight)

Make sure your site has:

• Sufficient room for deliveries and stacking blocks
• A compactor, screed tools, and cutting equipment
• PPE and safety fencing if working in residential zones

• Dig a trench that’s wider than the blocks and deep enough for your base materials.
• Lay a compacted gravel base and a bedding sand layer to the manufacturers specifications - see product installation guides.

• Start at the lowest point of your slope.
• Use a spirit level frequently — the first course must be perfectly level.
• Ensure blocks are firmly seated and tightly aligned.

• Stack each row with offset joints ("running bond").
• Most interlocking systems include a built-in setback for structural stability.
• Use a rubber mallet to tap blocks into place without damaging the face.

• Backfill with gravel behind each course.
• Install geogrid (if required) at manufacturer-recommended intervals.
• Compact soil behind the drainage layer.

• Use adhesive to secure cap blocks.
• Finish with matching caps, smooth-edged for seating or flat for structural simplicity.

In most states, walls over 500mm or walls supporting load (like driveways or buildings) must be engineered and council-approved.

• Skipping compaction — leads to sagging walls
• Inadequate drainage — causes hydrostatic pressure and failure
• Poor layout — curved walls need radius alignment tools or flexible jointing

• Always order extra blocks for cutting waste and damage.
• Pre-plan steps, corners and garden edges in your wall layout.
• Offer clients colour and finish options to suit their outdoor aesthetic.

Interlocking retaining wall blocks are the smart solution for builders seeking speed, efficiency, and quality. With proper preparation, product selection, and adherence to best practices, these systems provide durable, attractive walls that satisfy structural and visual goals.

View Austral Masonry’s retaining wall systems and make your next build smarter and stronger — block by block.

Here are answers to common questions when working with interlocking retaining wall blocks:

Laying a retaining wall starts with excavating a trench and preparing a compacted gravel base with a thin layer of bedding sand. Then, place the first course of blocks on the same alignment and level. Stack subsequent rows with offset joints, backfilling and compacting gravel behind each layer as you build.

To calculate the number of blocks needed for a wall, multiply the wall's length by its height to get the total square metres. Then, divide by the face area of one block. It’s advisable to add up to 10% extra to account for cuts, wastage, or future repairs.

The ideal backfill is free-draining material like 20mm crushed gravel placed directly behind the wall. It should be combined with a drainage pipe and filter fabric to manage water flow and prevent hydrostatic pressure.