Blocks may look similar once they are laid, but their weight, strength, thermal performance and suitability for different locations can vary considerably. Choosing the wrong type can make construction harder, reduce thermal or acoustic performance, and create problems when fixing cabinets or other heavy items to the finished wall.
The main options encountered on domestic projects are dense aggregate blocks, lighter aggregate blocks and aircrete blocks. “Concrete block” is often used as a general term for several of these products, so it is better to compare their actual properties and intended applications rather than relying on the name alone.
The main block types
Dense aggregate blocks are made using cement and relatively dense aggregates. They are heavy, durable and commonly used where strength, impact resistance, sound reduction or reliable fixing performance matters.
Lightweight and medium-density aggregate blocks use lighter aggregates and sit between dense blocks and aircrete. They can reduce handling weight while retaining some of the robustness associated with traditional concrete blocks.
Aircrete blocks, also known as aerated concrete blocks, contain many small air pockets. This makes them lighter and more thermally efficient. They can usually be cut with a specialist hand saw and are widely used in housing, extensions and internal walls.
The distinctions are easier to understand when comparing actual products rather than relying on broad terms alone. Gilmore Building Supplies groups its available masonry blocks by type, including aggregate and aircrete options, although individual strength grades and permitted applications should still be checked against the manufacturer’s technical information.
Block type comparison
| Consideration | Dense aggregate | Lightweight aggregate | Aircrete |
| Weight | Heavy | Moderate | Light |
| Ease of cutting | More difficult | Varies | Usually straightforward |
| Strength | Often high | Product-dependent | Available in several strength grades |
| Thermal performance | Relatively low | Moderate | Generally good |
| Thermal mass | High | Moderate | Lower |
| Sound reduction | Often good due to mass | Moderate to good | Depends heavily on the complete wall system |
| Fixing heavy loads | Usually straightforward with suitable fixings | Generally reasonable | Specialist fixings often needed |
| Below-ground use | Common for suitable products | Product-dependent | Only products approved for the application |
| Typical uses | Foundations, robust walls, garages and separating walls | General-purpose masonry | Cavity walls, partitions and thermally efficient construction |
These are general characteristics. Specifications vary between manufacturers and products, so strength, density, thermal conductivity and permitted uses should always be checked.
Dense aggregate blocks
Dense aggregate blocks are commonly used where durability and physical robustness are priorities. Their mass can also contribute to acoustic performance, making them useful for separating walls, workshops, garages and utility areas.
They are often chosen for foundations and below-ground work, although the specific block must still be approved for the conditions in which it will be used.
Pros:
- Strong and resistant to knocks
- Usually provides a secure base for shelves, cabinets and equipment
- High mass can improve sound reduction
- Suitable products are available for structural and below-ground applications
Cons:
- Heavy to carry and lay
- More difficult to cut and chase
- Higher thermal conductivity than aircrete
- Can slow progress on small or access-restricted projects
Dense blocks may suit garages, workshops, heavily used utility spaces and walls expected to support substantial fixings. Their weight does not automatically make them suitable for every structural application, however.
Lightweight and medium-density aggregate blocks
These blocks provide a compromise between the robustness of dense concrete and the handling benefits of aircrete. Their performance varies widely, so they should not be treated as one standard product type.
Some are designed for general internal and external masonry, while others offer particular benefits for strength, weight or thermal performance.
Pros:
- Easier to handle than dense blocks
- Often robust enough for general-purpose walling
- Can provide better fixing performance than very lightweight masonry
- Available in different strength and density grades
Cons:
- Performance is less predictable from the product name alone
- Not every product is suitable below ground
- Thermal performance may still require substantial insulation
- Cutting can be harder than with aircrete
They can be a practical choice for general walls where dense blocks would be unnecessarily heavy but aircrete is not preferred.
Aircrete blocks
Aircrete is widely used in domestic construction because it is light, easy to cut and relatively thermally efficient. It is especially useful where blocks need to be trimmed around openings, services or irregular details.
Different strength grades are available, including products intended for load-bearing walls. Aircrete should not therefore be regarded as suitable only for lightweight partitions.
Pros:
- Light and easier to handle
- Usually simple to cut and shape
- Lower thermal conductivity than dense concrete
- Useful for cavity walls, partitions and thermally efficient details
- Reduces the physical effort involved in laying and moving blocks
Cons:
- More easily damaged at exposed corners
- Heavy fixings require the correct aircrete anchors
- Lower mass may offer less acoustic benefit than dense masonry
- Not every product is suitable below ground or in exposed conditions
- Storage and handling require care to prevent saturation or damage
Aircrete often suits extensions, internal walls and the inner leaves of insulated cavity walls. Its suitability still depends on strength requirements, moisture exposure and the overall wall specification.
Strength and load-bearing considerations
Block strength is normally declared in newtons per square millimetre, written as N/mm². The required strength depends on the wall height, number of storeys, roof and floor loads, openings, lintel bearings and any concentrated loads.
A heavy block is not automatically strong enough for a particular structure, and the highest available strength is not always necessary. For load-bearing walls, beam supports, retaining walls and major alterations, the block specification should follow structural calculations or the project designer’s details.
The government’s Approved Document A provides guidance on structural safety, but it does not remove the need for project-specific design where loads or construction details are complex.
Thermal and acoustic performance
Aircrete generally provides better insulation than dense aggregate masonry at the same thickness. However, block type is only one part of the external wall.
The final thermal performance also depends on cavity insulation, wall thickness, mortar joints, plasterboard, render and the treatment of junctions around floors, roofs, windows and doors.
Dense masonry offers greater thermal mass and often better airborne sound reduction because of its weight. Acoustic performance still depends on the complete wall construction, including finishes, cavities and gaps around services.
Where a wall separates homes or residential rooms, it may need to follow a tested system that satisfies Approved Document E.
Moisture and below-ground use
General rules such as “dense blocks can go below ground” and “aircrete cannot” are unreliable.
Suitable dense aggregate blocks are widely used for foundations, but not every aggregate block is approved for that purpose. Some aircrete manufacturers also produce blocks specifically intended for foundation walls.
The correct choice depends on the product certification, ground conditions, drainage, sulphate exposure, damp-proofing and whether the wall is retaining soil. Below-ground and retaining structures should follow the engineer’s or manufacturer’s specification.
Fixing shelves and cabinets
Dense aggregate blocks generally provide a firm substrate for masonry screws, plugs and resin anchors. This is one reason they are often preferred in workshops, garages and rooms with heavy wall-mounted equipment.
Aircrete can also carry significant loads, but only when the correct fixing system is used. Ordinary universal plugs may not grip the material properly.
The fixing manufacturer should confirm the permitted substrate, fixing depth and safe load. Boilers, sanitaryware, large cabinets and cantilevered shelves may require specialist anchors, mounting rails or reinforcement designed into the wall.
Which block should you choose?
For a light internal partition, aircrete is often the easiest option to handle and cut.
For a garage or workshop wall that will carry tools, cupboards or shelving, dense or medium-density aggregate blocks may provide a more robust fixing surface.
For the inner leaf of an insulated cavity wall, aircrete may help improve thermal performance, provided the required structural strength is met.
For foundations, retaining walls and heavily loaded masonry, use only the block specified by the engineer, architect or manufacturer.
The best block is not automatically the strongest or lightest. It is the block whose verified properties suit the load, location, insulation strategy, intended fixings and complete wall design.
