F1 bricks are good for general purpose brickwork but are only moderately frost resistant.
Areas of concern include exposed garden and retaining walls, cills, cappings, chimneys and copings, and between ground level and a damp proof course.
An F2 brick, which has a higher degree of frost resistance, should be chosen in these and similar circumstances.
Compressive strength – 20 N/mm2.
Durability – F1/S2.
Frost resistance/durability – F1.
Water Absorption – 12%.