A Besser Block (sometimes known as a Bessa Block) is a hollow rectangular concrete block used in building construction.
What is the Standard Size of a Besser Block?
Besser blocks are made to suit a nominal 200mm metric system (known as 200 series blockwork) when you take into account 10mm grout between blocks.
Off the shelf a standard Besser Block measures 390mm long x 190mm high x 190mm wide. But when it is laid in a 10mm mortar then those dimensions become 400mm long x 200mm high (x 190mm wide).
You can also find Besser block in these sizes:
- 390mm long x 190mm high x 140mm wide. (known as 150 series blockwork).
- 190mm long x 190mm high x 190 wide.
- 390mm long x 190mm high x 290mm wide (300 series blockwork).
- 390mm long x 190mm high x 90mm wide (100 series bricks)
In construction, concrete Besser Blocks are stacked in layers called courses with half a block offset in what is called stretcher bond.
Besser blocks are ‘glued’ together with cement mortar joints. This is just a concrete glue trowelled between individual blocks to hold them together.
Steel reinforcement is placed horizontally in special blocks called knockout blocks as the wall is built. Steel reinforcement is also placed vertically in some of the hollow cores once a certain height of block wall is built.
Once the mortar has cured, a wall height of concrete block is filled with a special, flowable mix of concrete called grout (a mix of cement, sand and water that often uses smaller stones than normal concrete) to fill all or some of the hollow cores.
In Australia, it is now common practice to fill all of the hollow cores with grout. Even though more grout is used, builders find filling all cores with grout it faster which ends up saving money.
Besser Blocks Also Known As
In other parts of the world, Besser Blocks are also known as concrete blocks, grey blocks, breeze blocks and cinderblock construction.
In Australia, the common name for concrete blocks is Besser Block which comes from a prominent concrete block moulding equipment manufacturer, Besser.
Besser block retaining wall and raft slab
Besser blocks come in a variety of sizes. The most common block widths in Australian construction are 140mm (150 Series ) and 190mm (200 Series).
What are Besser Blocks Made From?
Besser blocks are made from concrete – a mix of sand, cement, water, stones, oxides and additives.
The holes and sides of a Besser Blocks are formed in a factory using a mould. Then the blocks are steam cured, wrapped and delivered to construction sites on pallets.
What are Bessa Blocks Used For?
Concrete blocks, when reinforced with vertical and horizontal steel reinforcement, are conventionally used to form external load-bearing walls in residential houses.
Concrete Besser Blocks can also be used to form retaining walls and even elevator walls in buildings up to 8 storeys.
How to Build a House with Bessa Blocks
When hollow concrete blockwork is reinforced with steel reinforcement and filled with concrete it becomes a very strong, durable external wall.
The best manuals for building with Besser Blocks are available at CMAA. https://www.cmaa.com.au/Technical/Manuals/technical-manuals
How to Build a Besser Block Retaining Wall
A besser block retaining wall can be built by a builder, a landscape gardener or by a professional block layer.
The best manual we have found for the design of besser block retaining walls is available for free from CMAA Besser Block Retaining Wallls.
Why Are Besser Blocks Popular
Besser Blocks are a popular form of construction because of a number of useful characteristics:
- When reinforced and filled with concrete, concrete block walls provide substantial structural strength and stability in residential houses. In cyclone areas, concrete walls are used because they have excellent impact resistance and have high bracing (racking capacity.
- When partially filled, concrete blocks have useful sound and fire insulating properties.
- For those looking for a different look, fancy architectural blocks are available from some suppliers including polished face blocks. These blocks are always a bit more expensive because they are denser concrete and have to be laid neatly.
- Besser blocks when laid below ground and reinforced can be used to retain fill under the slab.
Engineering Design of Clay Block Walls
In Australia, the structural design of clay blocks is often based on the excellent series of design and user manuals produced by the Concrete Masonry Association of Australia.
However first-principles design is guided by Australian standard AS3700.
Construction Issues with Concrete Blocks
- The external face of concrete cinder blocks needs to be waterproofed to prevent water penetration. Consult your block layer to determine your preferred waterproofing system.
- Waterproofing is especially important where concrete blocks are used as retaining walls for liveable space.
- Water penetrating concrete masonry walls often presents as efflorescence, a white crystalline salt on the surface of concrete masonry walls.
- Wall heights of more than 2500mm need to be filled in stages about 30 minutes apart to allow the grout to partially cure and become less fluid.
- Standard concrete masonry wall heights in residential construction are 2500mm (2100 to the top of doors and windows and a full 2 course ‘bond beam’ at the top of the wall and over openings; and 2700mm (2100mm to top of doors and windows and a full 3 course ‘bond beam’ at the top of the wall and over openings.
- Blockwork control joints are 10mm wide vertical breaks in concrete masonry walls to allow differential movement of adjacent panels. Their use is optional is fully reinforced concrete masonry walls in residential walls. Their use is highly recommended in retaining walls longer than 10m.
- Unreinforced blocks can move and crack. Correct positioning of the reinforcement is very important.
- The primary Australian documents that document the minimum construction requirements for concrete masonry walls in residential construction are: