Besser and concrete block sizes and when to use them

Besser is a brand name that stuck, the way people say it for any hollow concrete block. They are a workhorse of Melbourne building, and knowing the common sizes helps you plan a job.

Common block sizes

Concrete blocks are sized to lay on a 200 mm grid once you allow for the mortar joint. The usual face size is about 390 mm long by 190 mm high, and the thickness is what changes:

• 100 mm: thin walls, infill and lighter work.
• 150 mm: garden and retaining walls, single storey work.
• 200 mm: the standard structural block for most walls.
• 300 mm: heavier retaining and load bearing work.

There are also half blocks, and special shapes for corners, the top course and for hiding control joints. The hollow cores let you thread steel reinforcement down through the wall and fill them with concrete, which is what gives a block wall its strength.

When blocks beat brick

Blocks and bricks do different jobs. Blocks earn their place when you want structure and speed rather than a finished face:

• Retaining walls, where you need cores filled with steel and concrete to hold back soil.
• Garage, shed and boundary walls where strength matters more than looks.
• The structural backing behind a brick veneer or a rendered finish.

One block covers the same area as several bricks, so a block wall goes up faster. The trade off is the look. A raw block wall is plain, so it is usually rendered, bagged or hidden, where face brick is the finished surface in its own right.

Things to plan for

Block walls are heavy and often structural, so a few things matter:

• They need a proper footing sized for the load and the soil.
• Retaining walls almost always need engineering and drainage behind them.
• Reinforcing and core filling have to be set out before you lay, not after.

Get the footing and the steel right and a block wall will outlast everyone.

If you are weighing up block or brick for a wall, send a photo of the site and your suburb and we will tell you which suits the job and what it needs underneath.