A Besser Block (sometimes known as a Bessa Block) is a hollow rectangular concrete block used in building construction. A standard besser Block measures 390mm x 190mm x 190mm high.
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.
On site, concrete Besser Blocks are stacked in layers called courses with half a block offset in what is called stretcher bond. 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 and 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 that often uses smaller stones than normal concrete) to fill all or some of the hollow cores.
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 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).
Concrete Block Usage in Residential Structures
Concrete blocks, when reinforced with vertical and horizontal steel reinforcement, are conventionally used to form extenal load bearing walls in residential houses.
Concrete Besser Blocls can also be used to form retaining walls and even elevator walls in buildings up to 8 storeys.
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 need to be waterproofed to prevent water penetration. Consult your block layer to determine your preferred waterproofing system.
- Water proofing 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: