Question 1

1. What are Thermalite blocks made of?

Accepted Answer

Thermalite blocks are mainly made from a mixture of fuel ash (PFA) along with sand, cement, lime, and a small amount of aluminium powder. This combination reacts during the manufacturing process, creating their characteristic lightweight, cellular structure. The use of PFA, a recycled material, also contributes to their sustainability.

Question 2

2. What are the main benefits of using Thermalite blocks?

Accepted Answer

Thermalite blocks excel due to their outstanding thermal efficiency, helping to meet UK energy regulations and lowering heating costs. Their lightweight nature eases handling on building sites, speeding up construction without sacrificing structural soundness. They’re also notably workable, thereby reducing waste, which is a key cost concern.

Thermalite blocks also have inherent fire resistance, supporting safety, a key building code priority. Uniquely, they also often utilise PFA (a UK power station byproduct), aiding sustainability in construction.

Question 3

3. Can you use Thermalite blocks outside?

Accepted Answer

Yes. Thermalite blocks are commonly used in external walls, including cavity wall construction and foundations. However, they are typically used as the inner leaf and require suitable external finishes, such as render or facing brick, for weather protection.

Question 4

4. Are Thermalite blocks load bearing?

Accepted Answer

Yes, many Thermalite blocks are suitable for load-bearing applications, depending on their compressive strength rating. Lower-strength blocks are used for partitions, while higher-strength variants can be used in structural walls and foundations.

Question 5

5. What are Thermalite blocks used for?

Accepted Answer

Thermalite blocks are used across a wide range of applications, including internal partitions, external walls, foundations, and beam and block floors. Their lightweight nature and thermal performance make them common in modern masonry construction.

Question 6

6. Are Thermalite blocks fire rated?

Accepted Answer

Thermalite blocks are non-combustible and typically achieve an A1 fire rating. They provide good fire resistance but are not ‘fireproof’ in absolute terms, as performance depends on wall build-up and thickness.

Question 7

7. Are Thermalite blocks good insulation?

Accepted Answer

Yes. Thermalite blocks offer strong thermal insulation due to their air-filled structure, which reduces heat transfer and helps meet U-value targets in wall construction.

In practice, Thermalite blocks are used within cavity wall systems alongside insulation boards or full-fill insulation. The block provides a thermally efficient inner leaf, improving airtightness, reducing thermal bridging, and contributing to lower overall U-values. Using them doesn’t replace dedicated insulation materials but does support insulation by improving the baseline thermal performance of the wall.

Question 8

8. What fixings can I use with Thermalite blocks?

Accepted Answer

Thermalite blocks require fixings suited to aerated or lightweight concrete, as standard plugs may not achieve a reliable hold in lower-density material. Common options include:

Thermal block fixings (self-drive) – cut into the block to create a secure mechanical grip.
Aircrete or lightweight block anchors – threaded fixings designed for non-expansion fixing.
Helical fixings or twist nails – used for timber battens and drylining, driven directly into the block.
Frame fixings or concrete screws – suitable for heavier items when installed correctly.
Resin anchors – used where higher load capacity is required.

Standard expansion plugs can work for light-duty applications but may loosen in softer blocks. It’s best to use fixings designed for aircrete where possible.

Question 9

9. How many Thermalite blocks are there in a pack?

Accepted Answer

Pack sizes vary by supplier and format, but a standard pack typically contains around 60 -120 blocks. For small projects, blocks can usually be bought separately, and large-format units often come in packs of 3.

Thermalite blocks

Thermalite Solid Hi-Strength Block 7.3N 100mm

Thermalite 300mm Trenchblock T&G 3.6N

Thermalite Solid Shield Block 3.6N 100mm

Thermalite Hi-strength Block 7.3N 140mm

Thermalite 100mm Coursing Brick

Thermalite 100mm Turbo 2.9N Block

Thermalite Solid Part Wall Concrete Block 4N 215mm

Thermalite Solid Shield Block 3.6N 140mm

Hi-strength Thermalite Trench Blocks 7.3N 300mm

Thermalite Hi-strength Block 7.3N 215mm

Thermalite Solid Shield Block 3.6N 50mm