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’.
A standard block is 440 mm x 215 mm, the equivalent of 3 bricks high and 2 long, the maximum size that one person can comfortably lift. They are available in a range of widths from 50 mm to 300 mm.
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.
 Related articles on Designing Buildings Wiki
Featured articles and news
Apple's new HQ opened to employees this week, and has been touted as 'the best office building in the world'.
The risk of moisture in hard-to-treat buildings.
Find out about the intricate art of pyrography.
Have a look at this newly-opened linear park on an elevated highway in Seoul.
The charity for the blind wants to encourage greater collaboration with built environment planners.
Read our review of a new book examining methods used to observe how sustainable buildings work in occupation.
BRE and Loughborough University announce plans for a 'dementia-friendly' demonstration home.
CIOB launch new toolkit tackling the poor image construction still suffers among pupils in the 14-19 age group and their teachers.
Find out about adjudication in construction contracts with our introductory article.
BRE publish a new information paper: Understanding the factors affecting flashover of a fire in modern buildings.
London churches in the age of Wren, Hooke, Hawksmoor and Gibbs - Book review.
Our interview with Tom Dyckhoff about his new book 'The Age of Spectacle', starchitects, microhousing, the building he would demolish, and more...