What is the difference between Class A and Class B engineering bricks?

Class A engineering bricks have a minimum compressive strength of 125 N/mm² and maximum water absorption of 4.5%. Class B engineering bricks have a minimum strength of 75 N/mm² and maximum absorption of 7%. Class A bricks (typically blue/dark) are used for the most demanding applications — manholes, retaining walls, below DPC. Class B (typically red) are the more commonly used engineering brick for general below-ground and damp applications.

What does frost resistance rating mean for bricks?

Bricks are rated F0 (passive exposure — internal or protected), F1 (moderate exposure — most UK walls), or F2 (severe exposure — exposed parapets, retaining walls, copings, below DPC). F2 bricks can withstand repeated freeze-thaw cycles when saturated. Always use F2 rated bricks in vulnerable positions — using F0 or F1 bricks in severe exposure leads to spalling and frost damage.

What are London stock bricks?

London stocks are traditional yellow-brown facing bricks originally made from London clay mixed with ash. They have been the predominant brick in London and south-east England for centuries. Modern London stocks are manufactured to replicate the appearance and are available in various shades from yellow to grey. They are typically softer than engineering bricks with compressive strengths around 20-40 N/mm².

How many bricks do I need per square metre?

For standard UK bricks (215 x 102.5 x 65 mm) in stretcher bond, you need approximately 60 bricks per m² of single-skin wall, including 10 mm mortar joints. For Flemish bond (one-brick wall), it is approximately 120 per m². Always add 5-10% for waste and cutting. See our Brick Dimensions reference for detailed bond pattern quantities.

UK Brick Types & Specifications

Facing bricks, engineering bricks, commons, London stocks and Flettons with compressive strengths, water absorption and frost resistance.

UK Brick Classifications

Type	Min. Strength (N/mm²)	Max. Absorption (%)	Frost Rating	Typical Use
Engineering Class A	125	4.5	F2	Manholes, retaining walls, DPC
Engineering Class B	75	7.0	F2	Below ground, damp courses
Facing (pressed)	20–100+	Varies	F1–F2	Visible external walls
Facing (wirecut)	20–75	Varies	F1–F2	Visible external walls
Facing (handmade)	15–50	Varies	F1–F2	Heritage, premium finishes
Common (Fletton)	20–30	15–25	F0–F1	Internal walls, below render
London stock	20–40	8–15	F1	External walls (London/SE)
Calcium silicate	20–50	10–16	F1–F2	External walls, internal walls

Frost Resistance Classifications (BS EN 771-1)

Rating	Exposure	Suitable Locations
F0	Passive	Internal walls, rendered walls with overhang
F1	Moderate	Most external walls, sheltered positions
F2	Severe	Copings, parapets, retaining walls, below DPC, chimney stacks

Soluble Salt Content

Category	Salt Content	Risk of Efflorescence
S0	No requirement	May show efflorescence
S1	Low salt content	Low risk
S2	Very low salt content	Minimal risk, best for exposed work

Related Calculators

See the UK Brick Dimensions for standard sizes and bricks per m², or the Mortar Mix Ratios for the correct mortar to use with each brick type.

How We Calculate This

Frequently Asked Questions

Last updated: April 2026

All calculations are estimates. Verify with your supplier.

UK Brick Types & Specifications

UK Brick Classifications

Frost Resistance Classifications (BS EN 771-1)

Soluble Salt Content

Related Calculators

How We Calculate This

Frequently Asked Questions

Related Calculators

Concrete Mix Ratios

Insulation U-Values

UK Brick Dimensions

UK Cable Sizes