Class A vs Class B Engineering Bricks: What Is the Difference?
Class A vs Class B Engineering Bricks
If a specification calls for an engineering brick, one of the first choices is often Class A vs Class B engineering bricks. Both are high-performance clay masonry units, but their declared strength and water-absorption limits are different. Choosing correctly matters because the class is tied to performance rather than colour, price or visual finish.
Wienerberger's UK guidance states that Class A engineering bricks have compressive strength of at least 125 N/mm² and water absorption no greater than 4.5%, while Class B engineering bricks have compressive strength of at least 75 N/mm² and water absorption no greater than 7%. Those benchmarks make Class A the higher-performing category, but Class B remains widely used and may be exactly what a project requires.
Quick Comparison: Class A and Class B
| Property | Class A | Class B |
|---|---|---|
| Typical minimum compressive strength | 125 N/mm² | 75 N/mm² |
| Typical maximum water absorption | 4.5% | 7% |
| Common colour availability | Often blue | Red or blue |
| Main reason to choose | More demanding specified performance | High-performance general engineering masonry |
Use these figures as a comparison guide and always check the current declaration of performance for the exact brick you intend to buy.
What Does Class A Engineering Brick Mean?
Class A engineering bricks sit at the higher end of the traditional engineering-brick performance categories. Their very high compressive strength and low water absorption make them appropriate for details where those characteristics are explicitly required. A good example of a product in this category is a blue solid engineering brick manufactured to the relevant declared values.
Do not choose Class A simply because it sounds superior. A higher-strength unit may cost more, be heavier or be unnecessary for the wall you are building. The correct question is whether the structural and exposure specification requires Class A performance.
What Does Class B Engineering Brick Mean?
Class B engineering bricks are very common in UK construction. They still offer high compressive strength and low water absorption compared with many ordinary facing bricks. Products such as the Wienerberger Red Class B perforated engineering brick illustrate why Class B is not a 'low-grade' brick; it is a defined high-performance masonry product designed for demanding use.
Class B products can be red or blue, solid or perforated, depending on manufacturer and range. That is why visual identification is unreliable. Read the product title and technical data rather than trying to classify a brick by eye.
Is Class A Always Blue?
Class A engineering bricks are commonly associated with blue bricks, and Wienerberger's Class A range is blue. However, the safe buying rule is to verify class from the declared specification, not from colour. Dark blue colour is not a certificate of strength or water absorption.
Likewise, a blue engineering brick may be Class B. JJ Building Materials carries blue engineering products in different formats, so if your project calls specifically for Class A, filter your decision by technical properties rather than appearance. Read our blue engineering bricks guide for a broader explanation.
Can Class B Be Red or Blue?
Yes. Class B engineering bricks are available in both red and blue. Red Class B products are popular where a red brick appearance is preferred, while blue Class B units can provide the darker engineering-brick look without necessarily being Class A. Our red vs blue engineering bricks guide explains the practical differences.
Why Compressive Strength Matters
Compressive strength tells you how much compressive load the masonry unit can withstand under standard test conditions. It is expressed in N/mm². Class A's minimum benchmark is substantially above Class B's, but a wall does not derive its capacity from brick strength alone. Mortar, workmanship, wall thickness, eccentricity, restraint, openings, piers and the structural design all influence overall performance.
Where a structural engineer or drawing specifies a minimum unit strength, follow that requirement. Do not downgrade from Class A to Class B because the bricks appear similar, and do not assume that upgrading the brick allows you to change other parts of the design.
Why Water Absorption Matters
Water absorption is another key engineering-brick property. Lower absorption can be valuable in masonry exposed to moisture, frost and ground conditions. Class A has the lower maximum absorption benchmark, while Class B still has a low limit compared with many facing products.
Yet low water absorption does not make a wall waterproof. Damp-proof membranes, DPCs, cavity trays, drainage, copings, flashings, mortar joints and the surrounding construction all remain important. Engineering bricks should form part of a properly detailed moisture-management system.
Typical Uses of Class A Engineering Bricks
Class A may be specified for very demanding civil-engineering or structural details where the design requires its higher declared strength or lower water absorption. Examples can include specialist groundworks, retaining structures, heavily loaded masonry or environments where a Class A unit is explicitly called for.
Because applications vary, avoid using a generic list as a substitute for the specification. If a drawing states 'Class A engineering brick', buy a product that is actually declared as Class A and verify dimensions and configuration too.
Typical Uses of Class B Engineering Bricks
Class B engineering bricks are widely used in manholes, groundworks, retaining walls, selected damp-proof-course details and other structural masonry. The exact application depends on exposure and design. They are also useful where a robust engineering brick is required but Class A performance is not necessary.
JJ Building Materials stocks both red and blue Class B engineering products, allowing you to compare appearance, format and pack size within the engineering bricks collection.
Solid vs Perforated: Class Is Not Configuration
Another common source of confusion is the relationship between class and brick configuration. Solid and perforated describe the physical form of the unit; Class A and Class B describe performance categories. A Class B brick can be solid or perforated, and the configuration should be checked independently from class.
If replacing an existing brick or following a detail drawing, match both the required performance and physical format. Unit weight, handling and mortar bedding can differ between solid and perforated products.
Engineering Brick Size and Pack Quantity
Many engineering bricks use the familiar UK format around 215 x 102.5 x 65mm, but 73mm-high products also exist. Confirm dimensions carefully, particularly for extensions, repairs and tie-ins. Pack quantities vary too; examples in JJ Building Materials' range include packs around 368, 380 and 400 depending on product.
For quantity planning, read our how many engineering bricks do I need guide rather than relying on pack count alone.
How to Choose Between Class A and Class B
- Read the structural or architectural specification.
- Identify the required minimum compressive strength.
- Check the required maximum water absorption.
- Confirm whether a particular durability designation is specified.
- Choose the correct brick dimensions and solid/perforated configuration.
- Only then compare colour, brand, pack quantity and price.
This sequence prevents a common mistake: selecting a brick that looks right but does not satisfy the technical requirement.
Can You Substitute Class A for Class B?
A Class A brick exceeds the headline class benchmarks of Class B, but substitution should never be automatic. A product change can affect dimensions, configuration, weight, appearance, availability and other declared properties. If the work is specified or engineered, obtain approval before changing the masonry unit.
Can You Substitute Class B for Class A?
No, not without a design review. Class B does not meet the Class A benchmark simply because it is blue, solid or sold as an engineering brick. Where Class A is specified, use a conforming Class A product unless the responsible designer approves a change.
Class A vs Class B FAQs
Which is stronger, Class A or Class B engineering brick?
Class A has the higher minimum compressive-strength benchmark: 125 N/mm² compared with 75 N/mm² for Class B.
Which absorbs less water?
Class A has the lower maximum water-absorption benchmark at 4.5%, compared with 7% for Class B.
Are all red engineering bricks Class B?
Red Class B products are common, but always verify the exact declaration rather than classifying by colour.
Are all blue engineering bricks Class A?
No. Blue engineering bricks can be Class A or Class B.
Is Class A needed below DPC?
Not automatically. The correct class depends on the design, exposure and specification. Many projects use Class B where its declared properties satisfy the requirement.
Can Class B engineering bricks be load-bearing?
They can be used in structural masonry where the complete design allows it, but unit class alone does not determine wall capacity.
Does Class A look better than Class B?
No performance class guarantees a better visual finish. Engineering bricks are primarily manufactured for technical properties, and appearance can vary.
Where can I buy Class A and Class B engineering bricks?
Browse JJ Building Materials' engineering bricks to compare current red and blue products, then check the technical declaration for the exact brick before ordering.
Final Buying Advice
The simplest way to choose between Class A and Class B is to let the specification lead. Class A offers the higher strength and lower water-absorption limits, while Class B remains a robust and widely used engineering-brick category. Match class, dimensions, configuration and durability first; then compare colour, pack size and cost.