A concrete block is a rectangular unit manufactured from concrete, used to build walls and other structures. This simple definition barely scratches the surface of one of construction’s most versatile materials — from garden boundary walls to multi-storey buildings, concrete blocks form the backbone of modern masonry construction throughout the UK.
What Is the Difference Between a Concrete Block, Breeze Block, and Cinder Block?
This terminology confusion causes more misunderstanding than almost any other building materials question in the UK.
“Breeze blocks” and “cinder blocks” are older terms referring to blocks made using industrial waste as aggregate — specifically furnace clinker (breeze) or coal cinders. These materials created lighter blocks but with inconsistent properties and limited strength. The terms stuck in common usage even though the products they originally described are largely obsolete.
The modern standard product is the concrete block, manufactured using sand and fine gravel aggregates. Today’s concrete blocks offer superior strength, consistency, and performance compared to their historical predecessors. When someone asks for “breeze blocks” at a builders’ merchant, they’re typically supplied with modern concrete blocks that far exceed the capabilities of original breeze blocks.
Why Do Concrete Blocks Have Holes? The Engineering Behind the Hollow Core
The hollow cores running through concrete blocks represent engineering ingenuity, not cost-cutting. These voids serve multiple important purposes:
Weight reduction: A typical dense concrete block weighs around 20kg — manageable for construction workers. A solid block of equivalent size would weigh nearly double, slowing construction dramatically.
Thermal insulation: Hollow cores provide superior thermal insulation compared to solid concrete. The trapped air spaces reduce heat transfer, making hollow block construction more energy-efficient than solid masonry walls.
Structural reinforcement capability: The most significant benefit — when filled with concrete and steel reinforcement bars (rebar), hollow blocks create incredibly strong structural walls capable of supporting multi-storey buildings. This combines the convenience of block construction with the structural capabilities of reinforced concrete. For larger pours of fill concrete, our ready-mix concrete service provides the right grade for any application.
What Are the Two Main Types of Concrete Block?
Dense Concrete Blocks
Dense concrete blocks use standard aggregates like sand and gravel, creating heavy, strong units with excellent sound insulation. They typically weigh 19–22kg each and offer exceptional compressive strength, often exceeding 20 MPa when properly cured.
Best for: Foundation walls, load-bearing structural walls, party walls between properties, external walls requiring weather resistance.
Their density provides excellent thermal mass, helping moderate internal temperatures, whilst their weight contributes to superior sound blocking — crucial for party walls and external walls facing busy roads.
Lightweight Concrete Blocks
Lightweight aggregate blocks use materials like expanded clay, ash, or pumice, reducing weight by 30–50% compared to dense blocks whilst maintaining adequate strength for non-structural applications. These typically weigh 10–14kg each.
Best for: Internal partition walls, inner leaf of cavity wall construction, upper-floor construction where reducing structural loads matters, applications where thermal insulation takes priority over strength.
The reduced weight makes them easier to handle, speeds construction, and reduces structural loads on foundations.
How Are Concrete Blocks Related to Concrete Supply?
Concrete blocks are manufactured products — but the concrete that fills hollow blocks, beds them in mortar, or forms the surrounding structure must meet correct strength specifications. Our blog on concrete strength grades explains which grade suits different structural applications.
For filling hollow blocks or pouring surrounding foundations, our domestic concrete service covers residential projects across Yorkshire and the North West, and our commercial concrete service handles larger structural work. Use our free concrete calculator to estimate volumes for any surrounding concrete work.
Frequently Asked Questions About Concrete Blocks
How many concrete blocks are on a standard pallet?
Standard pallets typically contain 72–90 blocks, depending on block size and supplier packaging. Dense blocks are often packed in smaller quantities due to weight restrictions, whilst lightweight blocks may have higher counts per pallet.
Can you paint concrete blocks directly?
Yes, but surface preparation is crucial. Clean blocks thoroughly and apply appropriate masonry primer before finishing paint. The porous surface may require multiple coats for even coverage.
What’s the difference between 100mm and 215mm blocks?
These measurements refer to block width (thickness). 100mm blocks suit internal partition walls; 215mm blocks are used for external walls and structural applications requiring greater strength and insulation.
Are concrete blocks waterproof?
Standard concrete blocks are not inherently waterproof — they’re porous and will absorb moisture. For basements, retaining walls, or below-ground applications, either use rendered/sealed blocks or specify a waterproof concrete mix for surrounding poured concrete work.
What concrete should I use to fill hollow concrete blocks?
A C20 or C25 grade concrete with good workability is suitable for most block-filling applications. For structural reinforced block walls, your engineer will specify the required grade. Our team can advise on the right mix — call us or use the concrete calculator for volumes.
