- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 16 Jul 2018
Blocks are constructed using concrete or cement. They may include a hollow core to make them lighter and to improve their insulation properties. They have been in use since the 1930s when they were commonly used for the inner leaf of cavity walls. At this point they were made from an aggregate of stone or industrial waste such as clinker or breeze, hence the term ‘breezeblock’.
The kind of block selected for a particular application will depend on its:
- Load-bearing characteristics.
- Weight and handling properties.
- Thermal characteristics, such as U-value or thermal mass.
Dense blocks are usually made from cement, fine aggregate and course aggregate. They can be produced in a range of crushing strengths and tend to be used for structural purposes, such as foundations and load-bearing walls.
The advantage of lightweight blocks include their thermal insulation characteristics and ease of handling. During the last 80 years a variety of aggregates have been used - clinker blocks (8 parts clinker to 1 part cement), and blast furnace slag. They may be slightly more expensive than dense blocks
- Their closed cell structure means they have good resistance to water penetration.
- They provide good fire protection.
- They are easy to cut with a saw.
- They can accommodate fixings such as screws and nails.
For above ground uses, they might include mixes such as:
- cement : lime : sand 1 : 1 : 6
- cement : sand with plasticiser 1 : 6
- masonry cement : sand 1 : 5
- cement : lime : sand 1 : 2 : 9
Dense blocks are typically laid in mortars of average strength, 1:1:6 or 1:2:9. Stronger mortars may limit movement and may cause cracking of the blocks, although they are sometimes specified below ground level.
 Find out more
 Related articles on Designing Buildings Wiki
- Aircrete blocks.
- Brick sizes.
- Coal ash.
- Damp-proof course.
- Defects in brickwork.
- Defects in stonework.
- How to lay block paving.
- How to lay bricks.
- Lime mortar.
- Parge coat.
- Types of brick.
- Types of brick bonding.
Featured articles and news
Assembling, curating, caring for, and designing the future.
A sensitive approach to renovating a building of historic stature.
UK energy policy uncertainty as Welsh project put on hold
What collaborative working achieves and how it can be put in place.
BSRIA publishes the 2019 edition of its small but concise annual databook.
Using QSAND to measure the performance of disaster response.
What U-values are, why they matter and how they are calculated.
The need to ensure that we plan for all aspects of our bio-economy
BSRIA calls on government to reach deeper into the causes of pollution.
George Demetri brings a whole new level of technical knowledge to Designing Buildings Wiki.
Quality professionals need to take an active role in driving the completion process forwards.
The innovations needed to move from rhetoric to realisation.