What Is a Besser Block? Sizes, Types and How Block Walls Work

A Besser block is a hollow, rectangular concrete masonry block used to build walls in houses, retaining walls, sheds, pools and commercial and industrial buildings. In Australia the name is used for almost any standard grey concrete block. You will also see it spelt Bessa block, Besa block or Besser brick.

Besser blocks are useful because they come in standard modular sizes and are quick to lay. Their real structural strength, though, comes from what goes inside them: steel reinforcement placed vertically and horizontally through the hollow cores, which are then filled with concrete grout.

This guide covers Besser block sizes and types, how block walls are built, when they need to be filled and reinforced, and the problems we commonly see in existing block walls.

What Is the Standard Size of a Besser Block?

The standard full Besser block in Australia measures 390 mm long × 190 mm high × 190 mm wide. Laid with 10 mm mortar joints, each block takes up a 400 mm × 200 mm module in the wall. That is why the standard block is called 200 series.

Blocks are made in a range of widths, with the length and height kept the same so the courses line up:

Half blocks, typically 190 × 190 mm in face size, are used at wall ends and openings to keep the bond correct. The 150 series and 200 series are the most common widths in Australian residential construction.

How many Besser blocks per square metre? With a 400 × 200 mm module, a square metre of wall uses 12.5 full blocks. Add an allowance for half blocks, special blocks and breakage.

Sizes and the range of special blocks vary slightly between manufacturers, so confirm dimensions with your supplier.

Types of Besser Blocks

A reinforced block wall uses several block types, each with a specific job:

• Full (stretcher) blocks: the standard block used for most of the wall.
• Half blocks: used at ends, corners and openings to maintain the bond.
• H blocks: open-ended blocks that can be placed around vertical reinforcement rather than threaded over it.
• Knock-out (bond beam) blocks: blocks with webs that can be removed to create a horizontal channel for bond beams and lintels.
• Cleanout blocks: blocks with an opening at the base of the core. They let the block layer remove mortar droppings and let the reinforcement laps be inspected before the cores are grouted.

Cleanout blocks are easily overlooked, but they matter. If mortar droppings block the bottom of a core, the grout cannot fill it properly and the reinforcement may not be bonded where it is needed most.

How Besser Block Walls Are Built

Blocks are laid in courses, usually in stretcher bond, where each course is offset by half a block from the one below. The blocks are bedded in cement mortar, typically with 10 mm joints.

Vertical reinforcing bars are set into the footing as starter bars and extended up through the cores. Horizontal bars are placed in knock-out blocks to form bond beams and lintels.

Once the mortar has cured, the cores are filled with grout, a flowable concrete mix with smaller aggregate than normal concrete. Tall walls are usually grouted in stages in accordance with the engineer’s specification, because wet grout exerts considerable pressure on the blocks.

In Australian residential work it is now common to fill every core rather than only the reinforced ones. It uses more grout, but builders often find it quicker and simpler, and it avoids questions later about which cores were filled.

Do Besser Blocks Need to Be Filled?

For almost any structural wall, yes. Hollow, unfilled blocks have little resistance to sideways loads such as wind, soil pressure or impact. Reinforcement and grout are what turn a stack of blocks into a structural wall.

An unfilled block wall carrying only vertical load, such as a lightly loaded internal wall, may sometimes be acceptable. In practice, it is unusual for a load-bearing or retaining Besser block wall not to need reinforcement and core filling.

Do Besser Blocks Need to Be Reinforced?

Structural block walls need reinforcement, and its position matters as much as its presence. Bars placed against the wrong face of a retaining wall, or with too little grout cover, can leave the wall weaker than designed and more prone to corrosion.

Besser Block vs Cinder Block: What’s the Difference?

In everyday use, they mean much the same thing: a hollow building block. The names come from different places.

• Besser block is the common Australian name. It comes from Besser, a long-established manufacturer of block-making machinery.
• Cinder block is mainly an American term. It originally described blocks made with cinders or ash as aggregate. Australian Besser blocks are made from concrete, not cinders.
• Concrete block, concrete masonry unit (CMU) and blockwork are the technical and trade terms.
• Breeze block is a British term for a building block. In Australia it more often means a decorative screen block with open patterns, which is a different product.

What Are Besser Blocks Made From?

Besser blocks are made from concrete: cement, sand, aggregate and water, with oxides for colour and other additives as needed. The mix is pressed into moulds in a factory, cured and delivered to site on pallets.

What Are Besser Blocks Used For?

Reinforced and core-filled, Besser blocks are used for:

• external and load-bearing walls of houses, particularly in cyclone-prone areas;
• retaining walls, including walls retaining fill beneath a raised raft slab;
• basements and lower-level walls;
• sheds, workshops and industrial buildings;
• swimming pools;
• boundary walls and fences; and
• lift shafts and stair cores in low- and medium-rise buildings.

Why Are Besser Blocks Popular?

• Strength: reinforced and core-filled block walls are strong, stiff and resist impact well, which is why they are common in cyclone regions.
• Fire and sound: concrete masonry is non-combustible, and block walls can be designed to achieve fire-resistance levels and useful acoustic separation.
• Durability: properly built and protected block walls have a long service life with little maintenance.
• Speed and familiarity: modular sizes, a skilled block-laying trade and well-established design guidance make block walls straightforward to build.

Besser Block Retaining Walls

Reinforced Besser block is one of the most common materials for residential retaining walls. A well-performing retaining wall depends on four things working together:

1. a footing designed for the wall height, loads and ground conditions;
2. reinforcement of the right size, spacing and position;
3. properly filled cores; and
4. drainage and waterproofing behind the wall, so water pressure does not build up and moisture does not come through.

Drainage is the element most often skimped on, and in our experience it is behind many retaining wall problems. Our article on ag drains covers how to get subsoil drainage right.

The Concrete Masonry Association of Australia publishes detailed design and construction manuals for reinforced block retaining walls, available at cmaa.com.au.

In Queensland, retaining walls over 1 m high, and walls affected by loads such as nearby buildings, driveways or sloping ground (see retaining wall zone of influence), generally need building approval and engineering design. Check the requirements with your certifier or council before you build.

How Deep Should a Footing Be for a Block Wall?

There is no single answer. The footing for a structural block wall should be designed by an engineer, taking into account:

• the height and weight of the wall;
• whether the wall is retaining soil, and how much;
• the bearing capacity of the foundation soil;
• the reactivity of the soil; and
• any soft soil or loose fill beneath the footing.

Besser Block Pools

Reinforced Besser block is a well-proven way to build an in-ground or partly in-ground pool. Cornell Engineers has previously specified and inspected a number of block pools.

Two details matter most (there is more in our Besser block pool article). The walls and floor need to act together, so that water and soil loads on the walls are carried into the base. Ideally the cores and floor are filled in a single pour to avoid a weak joint where wall meets floor.

Fixing to a Besser Block Wall

Before fixing anything to a block wall, find out whether the core you are fixing into is filled. An anchor that works in solid, grouted blockwork may pull out of a hollow core, and the reverse also applies.

• Light fixings such as shelves and fittings can use masonry plugs and screws.
• Heavier fixings into core-filled blockwork commonly use mechanical anchors or chemical anchors, such as Ramset Chemset 101 Plus anchoring adhesive with Chemset anchor studs.
• Fixings into hollow blockwork need anchors specifically suited to hollow masonry. Follow the manufacturer’s guidance.

For structural connections, such as fixing a beam, deck or balustrade to a block wall, the anchors, edge distances and brackets should be specified by an engineer.

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Besser Block Adhesive

Masonry adhesives can be used to bond blocks in some applications, such as garden walls and landscaping. For a structural wall, an adhesive should only replace mortar if the engineer has specified it, because the wall’s design strength depends on what holds the blocks together.

Where a wall needs a fire rating, any adhesive used must also be compatible with that rating.

Exposed and Architectural Besser Block Walls

Exposed blockwork, especially polished or coloured architectural blocks, can look excellent. It does need planning. Usually only one face of the wall is the feature face, because it is difficult to source enough perfect blocks for a wall that is fully on show from both sides.

Architectural walls are still structural walls. Reinforcement, core filling and waterproofing need the same care as in any other block wall, with the added constraint that defects are harder to hide or repair.

Besser Block Alternatives

• Formed reinforced concrete walls: very strong and flexible in shape, but usually more expensive than blockwork of similar size.
• Precast concrete panels: cast flat and lifted into place. Common on industrial and commercial buildings where there are enough panels to justify the setup.
• Reinforced clay brick or clay block: similar principles to reinforced Besser block, with a brick appearance inside and out. These walls are relatively narrow, so accurate placement of reinforcement and adequate cover are critical.
• Insulating concrete forms: lightweight stay-in-place blocks filled with reinforcement and concrete. They insulate well but are less robust against impact, and retaining walls built with them need careful waterproofing.
• Autoclaved aerated concrete (AAC): light and easy to cut, but without the strength and robustness of reinforced blockwork.
• Dry-stacked blocks: blocks laid without mortar and finished with a surface coating. Rarely used in Australia and difficult to get right.

Construction Issues With Concrete Blocks

• Besser blocks are not waterproof. Walls retaining soil, especially beside habitable rooms, need a waterproofing membrane on the soil side and effective drainage behind the wall.
• Grout pressure: tall walls are usually grouted in stages to limit pressure on the blocks while the grout is fluid.
• Bond beams: residential walls commonly have a reinforced bond beam at the top of the wall and over openings.
• Control joints: vertical joints allow for movement between wall panels. In our experience they are particularly important in long retaining walls.
• Unreinforced or poorly reinforced blockwork can crack and move. Correct placement of reinforcement is essential.

The main Australian Standards for concrete masonry are AS 3700 Masonry structures and AS 4773 Masonry in small buildings.

Efflorescence on Besser Blocks

Efflorescence is the white, powdery or crystalline salt deposit that appears on the surface of blockwork. Water moving through the wall dissolves salts from the concrete, then leaves them behind when it evaporates at the surface.

Efflorescence is a symptom, not the problem itself. It shows that water is moving through the wall. How much that matters depends on where the wall is: some moisture in a garage wall may be tolerable, but the same moisture in a wall beside a bedroom usually is not.

Common sources of the water include:

• missing, damaged or poorly detailed waterproofing behind a retaining wall;
• blocked or inadequate drainage behind the wall;
• surface water directed towards the wall; and
• leaking pipes in or behind the wall.

The deposits themselves can be cleaned off with a product such as Crommelin Efflorescence Remover. If the water source is not dealt with, they will come back.

Fixing the cause might involve improving drainage behind the wall, reinstating waterproofing, redirecting surface water, installing a cut-off drain or treating the exposed face of the wall. The right fix depends on where the water is actually coming from.

Problems With Existing Besser Block Walls

Besser block walls are strong and durable when they are properly designed, reinforced, grouted, waterproofed and drained. Problems usually appear when one of those elements was inadequate, or when site conditions have changed since the wall was built.

Warning signs include:

• stepped or vertical cracking through the blockwork;
• a retaining wall leaning, bulging or moving;
• persistent damp, efflorescence or water entry;
• rust staining, which can indicate corroding reinforcement; and
• hollow-sounding blocks where the wall was expected to be core filled.

Cornell Engineers investigates problems in existing concrete masonry, including cracking, movement, water entry, retaining wall distress, deterioration and questions about whether a wall was built as designed. Our role is to work out what has happened, assess whether it matters structurally, and give practical advice on what should happen next. Where a dispute is involved, we also prepare independent expert reports.

If you have a problem with an existing block wall, send us the property address, photographs, a short description of what you have noticed and any drawings or reports you have. We will review the information and let you know whether the matter is a good fit for Cornell Engineers before preparing a fee proposal.

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Further Reading

• Concrete Masonry Association of Australia: design and construction manuals
• Forensic structural engineering