Clay Facing Brick Companies in the UK

Basic Facts about Clay brickwork

All natural materials used in construction are potentially vulnerable to damage and decay caused by exposure to the elements, organic decay or infestation.

Stone and brickwork used as facing material, in all types of masonry construction in particular, are at risk to a greater or lesser extent dependant on location, orientation and natural sheltering to damage caused by cyclic freezing and thawing.

This process involves a substantial thickness of material at or behind the exposed surface when it becomes saturated with water. The unsightly damage caused by 'spalling' can lead to further penetration of water into the structure. Repairs to this type of damage, particularly in older properties can be expensive and time consuming.

For designers in the UK the durability and in particular frost resistance of clay bricks is one of several critical factors influencing brick selection.

Other factors include:

• Size, modular co-ordination and dimensional stability
• Compressive strength
• Colour and texture
• Bond
• Mortar type and strength
• Soluble salt content

Most manufacturers offering a range of brick products are, therefore, seeking conformity and consistency in compliance with these specified performance requirements and the relevant British and European standards.

Clay and mud bricks have been in use for thousands of years. Excavating the clay; mixing it with other materials; forming it within moulds and the application of heat. Of course the process today is highly technical involving computer controlled kilns to produce semi-vitrified bricks of different hardness. It is the variations in this process from one brick type, or manufacturer to another that gives rise to differences in frost resistance.

Government and industry has since the 1950’s been engaged in research to agree a standard test to provide a reliable guide for this aspect of clay brick performance. The outcome of this was the publication of BS 3921 in 1985 which was superseded by BS EN 771-1 in 2006. This standard does not cover clay products used for paving. Pavers are covered by BS EN 1344.

The latter requires the manufacture to test bricks to a common standard and to categorise suitability of the product according to three levels of exposure.

• F0 Passive: bricks suitable for internal use; if used externally without protection will become damaged by frost action
• F1 Moderate: durable bricks except when saturated and subject to a freeze / thaw cycle
• F2 Severe: durable bricks where correctly detailed and installed in all conditions including saturated and exposed to freeze / thaw

Further guidance on the subject is available from BS 5628-3 “Code of Practice for the use of masonry-materials and components, design and workmanship”.

Though now withdrawn, it can be usefully read in conjunction with PD6697 which includes some information excluded from the old BS and omitted from BS EN 1996-2: Design Considerations, selection and execution of masonry.

Of course careful selection of bricks for the intended purpose and the detailing of adjacent elements can influence the weathering and durability of individual components. In other words, a brick designated F1 would perform better where other elements of construction assist with shedding rainwater or resisting frost. It is common practice, for example, to use a highly durable engineering quality red or blue brick at damp proof course level and below, in conjunction with a ‘softer’ less durable second hard yellow stock brick.

Elsewhere the Brick Development Association is a useful source of information.

Recommended reading includes BDA Design Note 7 “Brickwork Durability” which includes guidance upon design.