There are two classes of engineering brick available, Class A and the more widely used Class B. They are sold for their physical characteristics and not for their appearance as they are traditionally used where a strong durable brick is required and must have high compressive strength and low water absorption.
Their use for facing work should be avoided as they are not likely to have been inspected for minor chips or colour as would normally be the case with a smooth red or blue facing brick.
Class A engineering bricks can, in certain situations, be used as a damp proof course brick, and must have a compressive strength greater than 125N/mm2 and a water absorption less than 4.5 per cent. Class B engineering bricks have to achieve a compressive strength in excess of 75N/mm2 and a water absorption less than 7 per cent.