Durability Frost resistance

Bricks are classified into one of the three categories, F2, F1 and F0 according to their frost resistance within a standardised freezing test (Table 1.3). Only category

Table 1.3 Designation of freeze/thaw resistance and active soluble salts content for clay bricks

Durability designation

Freeze/thaw resistance


masonry subjected to severe exposure


masonry subjected to moderate exposure


masonry subjected to passive exposure

Active soluble salts content


sodium/potassium 0.06%, magnesium 0.03%


sodium/potassium 0.17%, magnesium 0.08%


no requirement

F2 bricks are totally resistant to repeated freezing and thawing when in a saturated condition. Category F1 bricks are durable, except when subjected to repeated freezing and thawing under saturated conditions. Therefore, category F1 bricks should not be used in highly exposed situations such as below damp-proof courses, for parapets or brick-on-edge copings, but they are suitable for external walls which are protected from saturation by appropriate detailing. Category F0 bricks must only be used where they are subject to passive exposure, as when protected by cladding or used internally.

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