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What is the difference between lightweight concrete blocks and regular blocks?

Posted by Lignacite

Tags: Lightweight Sustainability

Concrete blocks are a significant building material in modern construction, popular for their suitability across a wide range of uses, from external walls to flooring infills. What makes them even more versatile is the varying densities available, each designed to meet different thermal, structural, and acoustic requirements and efficiencies.

In this article, we'll discuss the key differences between two popular concrete block densities: regular (medium dense) blocks and lightweight blocks. With these comparisons, we aim to help you identify which block density you'll need for specific projects and why.

While it's not uncommon to hear people refer to 'standard' or 'regular' blocks (especially when comparing them to lightweight blocks), it's essential to properly distinguish between block types in order to really understand direct comparisons. In this article, you might see some references to standard blocks, which, in this case, are concrete blocks with medium-density. We'll also mention dense blocks where it's relevant.

Key differences between lightweight and standard blocks

While they typically appear visually similar, lightweight concrete blocks and medium-dense concrete blocks have several important differences, making them well-suited to contrasting situations and applications. Let's take a look at the fundamental differences between these block types.

Strength

A block's strength is defined by its compressive strength rating - its physical ability to withstand crushing forces without cracking.

Because lightweight blocks are made with more lightweight airy aggregates, medium-dense and dense blocks are almost always inherently stronger. However, that's not to say that a lightweight block cannot be a strong one - our Lignalite block, for example. has a mean unit strength of 7.3N/mm².

Manufacturers will sometimes counteract the reduced density of a lightweight block by increasing its thickness. This helps lightweight blocks reach a heavier-duty load capacity where needed, but means they are sometimes proportionally larger than standard concrete blocks.

Thermal performance

A block's thermal performance is defined by its ability to block heat transfer, which is measured by its thermal conductivity and resistance.

Because lightweight blocks are packed with air pockets, they typically have a low thermal conductivity. This makes them incredibly efficient at insulating, meaning they'll keep heat inside a building. In contrast, medium-dense blocks lack those air pockets, offering a moderate degree of thermal performance.

Airtightness

A block's airtightness is defined by its ability to prevent air from leaking through its structure. This is measured by how many cubic metres of air can permeate through a square metre of wall every hour. Airtightness is crucial for eliminating drafts and managing energy loss.

While a lightweight block's air pockets lend excellent thermal performance by trapping heat, their interconnected porous structure allows moving air to escape. When these blocks are left unfinished, their porous structure makes them more permeable.

Because of the tightly packed density of standard medium-dense blocks, this block type tends to allow far less air to escape through, and applying a finish to these blocks results in a highly superior airtightness.

Sound insulation

A block's acoustic performance is defined by its ability to prevent sound transmission between rooms or spaces. Density is needed to dampen airborne vibrations.

Lightweight blocks lack this heavy density, which inherently makes them a more moderate sound barrier when left unfinished. The heavy mass of a medium-dense block, however, lends excellent sound insulation performance. The compact aggregate naturally dampens airborne noise, even without a finish, making it highly efficient in blocking sound from travelling through walls.

Fire resistance

Lightweight concrete blocks and medium dense concrete blocks should both offer the highest possible non-combustible classification. Lignacite standard blocks, Lignalite lightweight blocks, and even our ultra-lightweight Fibo 850 blocks offer the same excellent Class A1 fire resistance in accordance with BS EN 13501- 1:2007+A1:2009.

Because they cannot catch fire, burn, or emit smoke, they are tested for how long a wall of blocks can stand up to intense heat before failing, rather than for flammability. Thicker blocks will inevitably last longer against extreme heat.

Benefits and limitations

Each block type comes with its own benefits and limitations, which is what makes them suited to different applications.

Benefits: lightweight blocks

• Safer manual handling - Because they are made of lower-density aggregates, these blocks are significantly lighter than their medium-dense counterparts to help prevent worker fatigue or injury.
• Reduced dead load - The low self-weight of lightweight blocks means a reduced overall dead load placed on a building's structure. This allows for a more economical building design.
• Improved thermal insulation - Lightweight blocks are engineered to contain more air than medium-dense blocks, which helps to reduce thermal conductivity. This means that less heat will be transferred between rooms, resulting in greater energy efficiency and more comfortable spaces during hot weather.
• Excellent fire resistance - Lightweight concrete blocks have a very good fire resistance, aided by their lower thermal conductivity. Lignalite lightweight concrete blocks and Fibo 850 ultra lightweight concrete blocks are classified with an A1 fire rating, meaning they are non-combustible.
• Ideal for new-build and refurbishment projects - Their lower weight aids manual handling, as well as minimising additional loads to the existing structure. Their low self-weight ensures easier transportation by hand through spaces with tight or restricted access.
• Good acoustic insulation - Despite being light, these concrete blocks easily meet standard building regulations for insulation between adjacent rooms.
• Sustainability - Lightweight blocks have a reduced density, which means they require fewer raw materials per unit to produce. They can also be made with recycled materials, such as ash and furnace slag, lowering environmental impact.

Limitations: lightweight blocks

• Not suitable when the highest compressive strength is needed - Lightweight blocks are available in a range of strengths, but the highest compressive strengths are generally achieved by medium-density and dense concrete blocks.
• Acoustic restrictions in separating walls - While ideal for preventing sound transmission from room to room, not all lightweight concrete blocks will meet Part E performance requirements. For some separating wall applications, such as between semi-detached houses or flats, medium-density blocks may be required to achieve the necessary acoustic performance.
• External exposure restrictions - Lightweight blocks may require additional consideration in exposed conditions. Certain grades can be used below ground, but suitability should always be checked against the application and exposure conditions.

Benefits: standard (medium dense) blocks

• High structural strength - Thanks to their excellent load-bearing capabilities, medium-dense blocks offer superior compressive strength. This makes them robust enough to be used in substantial structural applications.
• Enhanced acoustic insulation - Higher physical mass and low levels of porosity make standard concrete blocks a highly effective barrier against airborne sound.
• Superior airtightness - Medium-dense blocks have low air permeability, which greatly helps eliminate draughts and structural air leakage. If the block face is painted, this is enhanced even further.
• Unrestricted below-ground use - Medium-dense blocks are far less absorbent than lightweight blocks, making them highly durable against frost and saturation and more suitable for below-ground applications.
• Fewer external restrictions - Medium-density blocks are suitable for a wider range of external wall applications, subject to project requirements and exposure conditions.
• High durability and impact resistance - Their solid composition means standard medium-dense concrete blocks have high impact resistance, ideal for use in high-traffic environments.
• Excellent fire resistance - Medium-dense concrete blocks achieve very good levels of fire resistance. Lignacite standard concrete blocks are classified with an A1 fire rating, meaning they are non-combustible.

Limitations: standard (medium dense) blocks

• Reduced thermal insulation - Because the raw materials in medium-dense blocks are more tightly packed and lack the heavy concentration of porous air pockets found in lightweight blocks, their thermal conductivity is higher. This means heat escapes faster, which may require more cavity insulation to meet energy targets.
• Heavier substructure load - Medium dense concrete blocks are generally heavier than lightweight blocks. This additional self-weight will need to be accommodated by the supporting structure.
• Cutting and chasing - Standard concrete blocks are denser than their lightweight counterparts, and will need specific equipment to cut and chase, such as mechanical saws and rotatory chasing machines.

When should each concrete block type be used?

Thanks to the unique properties of medium dense and lightweight blocks, they can be used in different applications and environments.

Lightweight blocks, such as the Lignalite concrete blocks, combine strength and practicality while possessing a lower physical density, making them ideal for the following uses:

• Inner leaf of external cavity walls
• Outer leaves of cavity walls, provided they are rendered or receive a cladding treatment
• Infill panels in framed structures
• Refurbishments, conversions, and extensions
• Weight-sensitive builds
• Tall partitions walls
• Infill for block and beam flooring (although you may need to specify 7.3N/mm2 blocks for this application)

Due to their high durability, massive versatility, and exceptional resistance to noise and air leaks, medium-dense concrete blocks, e.g. Lignacite GP and Lignacite SP blocks, are best suited to:

• Below-ground
• Separating walls
• ƒstInner and outer leaves of external cavity walls
• High-load-bearing structures
• Structural fire-break walls
• Infill for block and beam flooring

Lightweight and medium-dense concrete blocks from Lignacite

When choosing between lightweight and medium-dense masonry, it ultimately comes down to structural load, environmental exposure, and the technical targets of your build.

Our lightweight blocks provide an agile and highly insulative solution, maximising thermal performance and keeping manual handling safe and efficient, and we offer two ranges to meet these needs: the lightweight Lignalite and the ultra-lightweight Fibo 850.

Meanwhile, our medium-dense Lignacite concrete blocks are an excellent choice for fair face and directly painted walls, below-ground durability, and acoustic and fire containment. Each density comes with its own long list of advantages, enabling you to choose the right block for the task with confidence.

By understanding how these different densities scale across strength, sound, airtightness, and other important factors, you'll be better placed to strategically specify the right block for the job.

If you would like to understand more about our lightweight and medium-dense blocks and their suitable applications, don't hesitate to get in touch with the Lignacite team.