A retaining wall holds back soil on a sloped block, stops erosion, and creates a flat, usable section of yard. Brick is one of the most common retaining wall materials in Australia because it is widely available, easy to source second-hand, and simple to match to an existing house facade. This guide covers brick selection, the build method, drainage, and the council rules that apply in most Australian states.
What a Retaining Wall Actually Does
A retaining wall resists the lateral pressure of soil, particularly after rain when saturated soil is significantly heavier and pushes harder against the wall face. Three things determine whether a wall holds:
- A solid footing below the frost/movement line
- Drainage behind the wall so water pressure does not build up
- A wall material and bond pattern rated for the height and load
Walls under roughly 600mm (about knee height) carry low risk and are a reasonable DIY project for most homeowners. Anything taller, or any wall supporting a driveway, deck, or structure, should be checked by a structural engineer before you start.
Choosing Bricks for a Retaining Wall
The Brick Pit supplies three brick types commonly used in retaining wall projects — see our full recycled bricks range for state-specific stock.
Recycled Bricks
Reclaimed from pre-1950s demolition sites. Good for garden walls and heritage-style properties where colour matching to an existing house matters. See our recycled bricks for current stock and grades.
Sandstock Bricks
Australia’s earliest brick type, hand-moulded from roughly the 1800s to early 1900s, also known as convict bricks. Denser and rougher-textured than machine-pressed bricks, which suits taller, load-bearing walls. Full details on our Sandstocks product.
Paving Bricks
Flatter and smoother than sandstocks. Suitable for low retaining walls under roughly 600mm, garden edging, or walls that double as informal seating. See our Paving Bricks product.
| Recycled Bricks | Garden walls, heritage-style properties | 450 |
| Sandstock Bricks | Taller, load-bearing walls | 500 |
| Paving Bricks | Low walls under 600mm, seating edges | 400 |
Mortar Mix for a Retaining Wall
A standard retaining wall mortar mix is 1 part cement to 4–5 parts sand, with enough water to reach a firm, workable consistency. Mortar sets within 24–48 hours but does not reach full design strength until around 28 days, so avoid backfilling or loading a new wall before that point.
How to Build a Brick Retaining Wall
- Dig the footing trench: at least 150mm deep for a low wall, deeper for taller walls — your engineer or local council can confirm the requirement for your wall height and soil type.
- Lay a compacted gravel base: this lets water drain away instead of pooling against the footing.
- Lay the first course on a string line: mortar each joint and check level with a spirit level every few bricks.
- Install drainage behind the wall: a perforated pipe or gravel drainage layer behind the bricks, with weep holes at the base, relieves water pressure that would otherwise push the wall over.
- Backfill in stages: compact backfill in layers rather than all at once, to avoid uneven loading while the mortar cures.
Common Mistakes That Cause Wall Failure
- No drainage layer: the single biggest cause of bowing or collapsed retaining walls in our experience — trapped water pressure has nowhere to go.
- Skipping council approval: most Australian councils require a permit for walls over roughly 1 metre, and some require engineering certification above 600mm. Rules vary by council and state, so check with your local authority before building.
- Mixing brick types without planning: combining recycled and sandstock bricks can look intentional and attractive when planned, but looks patchy when it happens by accident mid-project.
DIY or Hire a Professional?
Low walls under roughly 600mm with stable, well-drained soil are a reasonable DIY project for someone comfortable with basic bricklaying. For anything taller, anything supporting a structure (deck, driveway, pool), or sites with poor drainage or unstable soil, engage a structural engineer and a licensed bricklayer. The cost of getting it engineered correctly is far lower than the cost of rebuilding a failed wall.
Why Choose The Brick Pit
The Brick Pit has supplied recycled and heritage bricks across Australia since 1975. For retaining wall projects, we can help with brick selection, colour and texture matching, and quantity estimates based on your wall dimensions. Browse our recycled bricks range, view Sandstock Bricks and Paving Bricks product details, or contact our Smithfield yard to discuss your project.
Frequently Asked Questions
Can I use paving bricks for a retaining wall?
Yes, for walls under roughly 600mm or decorative edging. For anything taller, sandstock bricks or engineered block are a stronger choice.
How long does mortar take to dry?
Mortar sets within 24–48 hours but reaches full strength at around 28 days. Avoid backfilling or loading the wall before then.
Do I need a permit to build a retaining wall in Australia?
Permit requirements vary by council and state. Many councils require approval for walls over 1 metre, and some require engineering certification above 600mm. Check with your local council before starting.
How many bricks do I need for a retaining wall?
This depends on wall length, height, and brick size. Use our brick quantity guide to estimate, or contact us with your wall dimensions for an exact count.
