External masonry walls

6.1

6.1.9Bricks

Bricks shall be capable of supporting intended loads and have appropriate resistance to the adverse effects of freeze/thaw and sulfate attack.

The design strength of bricks should comply with:

  • BS EN 1996-1
  • the design.

Clay bricks

Table 3: Classification of clay bricks according to their freeze/thaw resistance and active soluble salt content in accordance with BS EN 771-1

DurabilityFreeze/thaw resistanceActive soluble salt content
F2,S2Freeze-/thaw-resistant (F2), durable in all building situations(S2) low
F2,S1Freeze-/thaw-resistant (F2), durable in all building situations(S1) normal
F1,S2Moderately freeze-/thaw-resistant (F1), durable except when saturated and subject to repeated freezing and thawing(S2) low
F1,S1Moderately freeze-/thaw-resistant (F1), durable except when saturated and subject to repeated freezing and thawing(S1) normal
F0,S2Not freeze-/thaw-resistant (F0), liable to be damaged by freezing and thawing(S2) low
F0,S1Not freeze-/thaw-resistant (F0), liable to be damaged by freezing and thawing(S1) normal

Bricks that are freeze-/thaw-resistant (F2,S2 or F2,S1 to BS EN 771) should be used where there is a high risk of prolonged wetting and freezing including:

  • external facing work in Scotland
  • exposed parts, including copings, sills, parapets and chimneys which have no overhang to provide protection.
  • areas of the country subject to exceptionally severe freeze/thaw exposure. See Clause 6.1.6.

In areas of severe freeze/thaw exposure outside Scotland, bricks that are moderately freeze-/thaw-resistant (F1,S1 or F1,S2 to BS EN 771) may be used for general wall areas, provided they are classified in the manufacturer’s published recommendations as satisfactory for the exposure. Further guidance can also be found within the Brick Development Association “Severely exposed brickwork” publication.

Bricks that are not freeze-/thaw-resistant (F0,S2 or F0,S1 to BS EN 771) are not acceptable for use externally, unless completely protected by a cladding which can satisfactorily resist the passage of water.

Where brickwork may become saturated, moderately freeze-/thaw-resistant bricks (F1,S1 or F1,S2 to BS EN 771) are not appropriate where there is a risk of vulnerability to frost. In saturated conditions, sulfate-resisting cement mortar is required for S1 designation bricks.

For one and two storey homes, clay bricks to BS EN 771, with a minimum compressive strength of 9N/mm2 should be adequate.

For three storey homes; clay bricks to BS EN 771 with a minimum compressive strength of 13N/mm2 are acceptable.

Tolerances of clay bricks

Guidance on tolerances for clay bricks can be found within the BDA publication Designing to brickwork dimensions.

Concrete bricks

Concrete bricks have a direct relationship between strength and durability, including freeze/thaw resistance. Most concrete bricks have a strength of 22N/mm² and are durable in most situations and are equivalent to frost resistance class F2 for clay bricks. For copings and sills, bricks with a compressive strength of 36N/mm² should be used. For one, two or three storey homes, concrete bricks to BS EN 771-3, having a minimum compressive strength of 22N/mm² are acceptable.

Reclaimed bricks

  • should be used in accordance with Technical Requirement R3
  • if the durability category cannot be determined and may require independent certification of suitability
  • may require independent certification of suitability
  • may be unsuitable for external work because of a high salt content or a lack of freeze/thaw resistance
  • which have previously been used internally or which were fully protected may be unsuitable in external situations..

It is advisable to know where reclaimed bricks came from, and if they were used internally or externally.

Special shaped bricks (only applicable to clay bricks and concrete bricks)

Special shaped bricks should conform to BS 4729.