Concrete blocks explained: dense, lightweight and aircrete

2 min read

Concrete blocks do the heavy lifting behind the scenes — usually the inner skin of a cavity wall, hidden once the plaster and facing brick go on. But not all blocks are the same, and choosing the wrong type affects strength, insulation and how easy the wall is to build.

Dense concrete blocks

The strongest and heaviest option, used where load-bearing capacity matters most — foundations, retaining structures and the lower courses of taller walls. They’re hard-wearing but offer little thermal insulation on their own.

Lightweight concrete blocks

Made with lighter aggregates, these are easier to handle and cut while still carrying good loads. A sensible all-rounder for the inner leaf of a domestic cavity wall, balancing strength, weight and cost.

Aircrete blocks

The lightest of the three, packed with tiny air bubbles that give excellent thermal performance. Ideal where insulation is the priority and loads are moderate. They saw through easily, which speeds up cutting around openings.

Which block for which job?

• Load-bearing / below ground: dense.
• General inner-leaf blockwork: lightweight.
• Insulation-led builds: aircrete.

Browse the full concrete blocks range, or see everything in bricks & blocks if you’re specifying the whole wall.

Pairing blocks with brick

The inner block leaf usually sits behind a facing brick outer skin. The brick count for the outer leaf doesn’t change whether you build solid or cavity — our post on bricks per m² covers the maths.