Keep bricks and brickwork dry.
Frost attack is much more likely if the brickwork is saturated.
BS 8000: part 3 (2001) and BS 5628: part 3 -
"Bricks should not be laid at temperatures below 3°C on a falling thermometer".
Water expands by about 10% in volume when it turns into ice, forcing mortar apart and breaking the bond.
Calcium chloride (anti-freeze) cannot be used in mortars as there is insufficient mass to deal with it.
Air entrainment reduces the total amount of water necessary in the mix and is the most effective means of frost protection as it provides space for the water to expand if it freezes.
C & G mortars contain air entrainment in accurately controlled quantities.
Retarded mortars left in skips overnight in freezing conditions should be well protected from frost. If affected, the mortar should not be used.