Understanding Brick Grades and Classifications: What Do the Codes Mean?

For anyone working in the trade, knowing your materials inside out is key to getting the job done right. When it comes to bricks, understanding grading and classification is crucial for selecting the right product for structural integrity, longevity, and compliance with building regulations.

If you’ve ever come across terms like F2, S2, or EN 771-1 and wondered what they actually mean in practice, this guide will break it down.

Brick Classifications: What Do They Tell You?

Bricks are classified based on their physical properties, including strength, durability, water absorption, and resistance to frost. The two key standards you’ll see in the UK are:

British Standard (BS 5628 & BS EN 771-1)

• BS 5628 (now largely replaced) was the original masonry design standard, covering load-bearing strength and durability.
• BS EN 771-1 is the European standard that replaced it, setting out the specifications for clay bricks used in masonry.

Frost Resistance Grades (F1 & F2)

The frost resistance rating tells you how well a brick can withstand repeated freezing and thawing cycles without cracking or spalling.

• F2 (High frost resistance): Suitable for external walls exposed to severe weather conditions. Ideal for façades, boundary walls, and areas prone to moisture.
• F1 (Moderate frost resistance): Can be used externally but only in sheltered locations where direct exposure to rain and frost is limited.
• F0 (No frost resistance): Not suitable for external use. Typically used for internal walls or decorative applications.

If you’re working on an exposed site, always check for F2-rated bricks to prevent long-term weather damage.

Strength and Load-Bearing Classifications

Different jobs require different levels of compressive strength in bricks. This is measured in N/mm² (Newtons per square millimetre) and determines how much load the brick can take before it fails.

Common Strength Ranges:

• 7-20N/mm²: Suitable for non-load-bearing walls, internal partitions, and general use.
• >20N/mm²: Used for structural applications, external walls, and high-load areas.
• Engineering bricks (Class A & B): Designed for extreme load-bearing capacity and durability.

What About Engineering Bricks? Class A vs Class B

Engineering bricks are specifically manufactured for strength and low water absorption, making them a tough, reliable choice.

• Class A (125N/mm², <4.5% water absorption): The highest strength, used for structural applications like foundations, tunnels, and below-ground work.
• Class B (75N/mm², <7% water absorption): Highly durable but slightly lower strength than Class A. Used in retaining walls, damp-proof courses, and civil engineering work.

If you’re working on load-bearing structures, make sure you’re using bricks with the right compressive strength to avoid structural issues down the line.

Water Absorption and Durability Ratings

A brick’s ability to resist moisture is just as important as its strength, particularly in external applications.

• High water absorption (12-20%): Suitable for internal walls and non-exposed areas.
• Low water absorption (<7%): Essential for external brickwork to prevent damp issues.
• Very low absorption (<4.5%): Found in Class A engineering bricks, offering maximum resistance to water penetration.

If you’re working on retaining walls, basements, or exposed façades, choosing low-absorption bricks will help prevent issues like frost damage and efflorescence.

Specialist Brick Classifications

When working with specific applications, there are additional classifications to consider:

• Facing bricks: Designed for external walls where appearance matters. These can be wirecut, handmade, or pressed.
• Common bricks: A basic, lower-quality option for internal walls or hidden applications. These won’t be frost-resistant.
• Fire bricks (Refractory bricks): Manufactured for high-temperature environments, such as fireplaces, kilns, and furnaces.
• Perforated and hollow bricks: Used to reduce weight and improve insulation while maintaining structural integrity.

How to Make Sure You’re Choosing the Right Brick

Every job is different, and choosing the wrong brick can lead to costly issues. To avoid this, check these factors before ordering:

1. Where is the wall located? If it’s exposed to the elements, use F2 frost-resistant bricks.
2. Is it load-bearing? Look at the compressive strength rating and choose accordingly.
3. Does it need to be waterproof? Low water absorption is critical for external walls and below-DPC applications.
4. Are there aesthetic requirements? Facing bricks come in various colours and finishes to match existing brickwork.
5. Are there local regulations? Conservation areas and heritage projects may require bricks that match traditional materials.

Find the Right Bricks at Lords

Understanding brick grades and classifications is essential for choosing the right product for your project. At Lords Builders Merchants, we stock a full range of facing bricks, engineering bricks, and specialist masonry solutions, helping you meet the demands of any job.

Need advice? Speak to our team in branch, and we’ll help you source the right materials for your next project.

Find your nearest Lords branch or browse online today.