A besser block retaining wall is one of the strongest options for managing sloped land. Long-term performance depends on getting the reinforcement, core fill, and drainage right from day one.

 

Why Besser Blocks Are a Strong Choice for Retaining Walls

Managing a sloped yard or eroding embankment in the Hawkesbury, Hills District, or Blacktown? A besser block retaining wall is one of the most reliable structural solutions available. Besser blocks — formally known as hollow concrete masonry units — suit this kind of work well. Their uniform dimensions make block laying efficient. Their hollow cores serve a critical structural function beyond reducing weight. Those cavities accept vertical steel reinforcement. Concrete then packs them solid, creating a wall that behaves much like a poured concrete structure.

That distinction matters. A dry-stacked segmental block wall relies on weight and interlocking shape alone. A properly built besser block retaining wall is a bonded and reinforced system. Mortar holds the courses together. Steel resists bending and overturning forces. Core fill ties everything into a single rigid mass. That combination handles significant lateral pressure from soil, water, and surface loads. It’s why builders choose besser block walls for retained heights above 600 millimetres. Before you specify materials, explore the range of retaining wall blocks available. It’s a good first step for any project.

 

Building on Solid Ground: The Footing

Every besser block retaining wall begins below ground. The footing is not optional. A reinforced concrete footing distributes the wall’s load across a larger area of ground. It anchors the base against movement and gives you a level surface for the first block course. Without it, the wall above will eventually shift, settle unevenly, or lean under pressure.

Form the footing in a trench dug down to firm, undisturbed ground — not topsoil or loose fill. Before you pour the concrete, set starter bars into the wet mix at precise intervals. Position them to align exactly with the hollow cores of the first block course. These bars project upward and later tie into the vertical reinforcement running through the full height of the wall. Once you pour the footing, allow at least seven days to cure before block laying begins. Cutting that time short weakens the bond between the footing and the bars. That weakness will show up later under load.

 

Reinforcement: The Steel That Makes It Structural

Reinforcing steel is what separates a decorative masonry feature from a genuinely structural retaining wall. Once block laying begins, thread vertical steel bars through the hollow cores. Tie them securely to the starter bars below. As each course goes up, add horizontal reinforcement at specified intervals. This resists the tendency of the wall to bow outward under soil pressure.

Choosing the Right Bar and Spacing

For most residential retaining walls in Australia, builders use deformed steel bars for vertical reinforcement. N12 or N16 are the most common choices. The spacing between bars depends on the wall’s height and the load it carries. For walls up to around 1.5 metres, place vertical bars at 400 millimetre centres. Taller walls or those under heavier loads may need bars at 200 millimetre centres. Paving, driveways, or structures above the wall all increase the load. Add horizontal ties in those situations too.

Accurate positioning matters considerably. The bars need to sit approximately 55 millimetres from the back face of the wall. This achieves the correct concrete cover and ensures composite action between the steel and the core fill. Before grouting, tie all bars securely in place so they can’t shift when you pour the concrete. If the pour shifts any bars out of position, you compromise the finished wall’s structural integrity. You can’t fix that kind of defect after the fact.

 

Core Fill: Why Every Core Needs to Be Filled

Once you’ve laid the blocks and correctly positioned the steel, fill every hollow core in the wall with concrete. This transforms the individual blocks into a single continuous structure. It can then resist the forces a retaining wall faces.

A common misconception is that only the cores holding steel bars need filling. That’s not the case. Fill all cores — reinforced or not. Leaving voids creates weak points. These can crack or deteriorate under sustained pressure, particularly when water moves through the retained soil. For core fill, use cement products in a 20 MPa concrete mix. Keep the maximum aggregate size to 10 millimetres. The smaller aggregate lets the mix flow freely through the cores without bridging or leaving air pockets. Pour the fill in lifts — generally no more than 1,800 millimetres at a time. Compact each lift thoroughly with a rod or pencil vibrator. After filling the cores, allow at least another seven days to cure before you start any backfilling.

 

Drainage: The Step That Protects Your Investment

Even a well-built besser block retaining wall will deteriorate without proper drainage. Water is the leading cause of retaining wall failure. As soil behind the wall absorbs water, it increases in weight and expands. This generates hydrostatic pressure that pushes outward against the wall face.

If that pressure has nowhere to go, it will eventually crack mortar joints or displace blocks. Over time, it can also cause the wall to tilt outward. This often happens well before the concrete nears the end of its service life.

The Three Components of a Good Drainage System

The drainage design behind a besser block retaining wall involves three elements working together.

First, place a layer of clean crushed aggregate — at minimum 300 millimetres wide — directly behind the wall. This natural aggregate layer lets groundwater move freely downward rather than building up in the retained soil. Angular, clean-crushed rock performs far better than round pea gravel or sand. Both compact over time and restrict drainage flow.

Second, lay a 100 millimetre slotted PVC drainage pipe at the base of that aggregate layer. Keep it on a consistent downward slope so water discharges freely beyond the ends of the wall. Wrap the pipe in a geotextile fabric sock. This keeps fine soil particles from entering and clogging it over time. Using quality drainage and irrigation products from the start saves you the cost of remediation later.

Third, where there’s no clear discharge point for the drainage pipe, form weepholes in the base course of the wall. Space them at approximately 1,200 millimetre intervals. These short PVC inserts let accumulated water escape through the front face. Also, grade the surface at the top of the retained area away from the wall. Seal it with a low-permeability finish. This stops surface runoff from adding to the problem.

 

Height, Engineering, and Council Approval

In NSW and across most of Australia, retaining walls above 600 millimetres require a development application or building permit. A structural engineer generally needs to design and certify walls exceeding 1,000 millimetres. Councils almost always classify anything above 1.5 metres as an engineered structure under AS4678.

Beyond height, other factors can trigger engineering requirements. Proximity to a boundary, heavy surcharge loads like driveways or buildings, and the type of retained soil all play a role. Check with your local council before construction begins. This keeps you compliant and ensures you have certified documentation for resale and future building inspections. Keep records of the materials used and the design specification. That paper trail pays dividends down the track.

 

Ready to Build? Source Your Materials from Parklea Sand & Soil

Parklea Sand & Soil has been supplying builders, tradies, and homeowners across the Hawkesbury, Hills District, and Blacktown since 1988. From concrete blocks and aggregates to cement products and drainage materials, everything you need for a besser block retaining wall is available. Choose delivery or collect from the yard.

Call us on (02) 4572 7549, or visit us at 729 George St, South Windsor. We’re open Monday to Friday 7am–5pm and Saturday 7am–1pm. Tell us about your project and we’ll help you get the right materials sorted.

 

Frequently Asked Questions

What is a besser block retaining wall?

A besser block retaining wall is a structural wall built from hollow concrete masonry blocks. The blocks are laid in courses with mortar, reinforced with steel bars through the hollow cores, and filled with concrete to create a solid, load-bearing structure capable of holding back large volumes of soil over the long term.

How tall can a besser block retaining wall be without engineering?

In most parts of Australia, retaining walls above 600 millimetres require a building permit, and walls above 1,000 millimetres typically require sign-off from a structural engineer. Walls above 1.5 metres should be designed to AS4678. Requirements vary by council, so always check locally before you build.

Do all the cores in a besser block retaining wall need to be filled?

Yes — all hollow cores are filled with concrete in a correctly built besser block retaining wall, not just those containing reinforcement bars. Unfilled cores create weak points that can crack or deteriorate under sustained soil pressure, particularly when water is also present in the retained material.

What drainage is required behind a besser block retaining wall?

A proper drainage system includes at minimum 300 millimetres of clean crushed aggregate behind the wall, a 100 millimetre slotted PVC drainage pipe at the base wrapped in geotextile fabric, and weepholes at regular intervals if there is no end-discharge point. The surface above should also be graded away from the wall.

How long should you wait before backfilling a besser block retaining wall?

After the cores have been filled with concrete, the wall should cure for a minimum of seven days before backfilling begins. Starting too early puts lateral pressure on the wall before the concrete has reached adequate strength, which can cause cracking or movement in the freshly filled cores.