Engineering bricks are a type of brick used where strength, low water porosity or acid (flue gas) resistance are needed. Engineering bricks can be used for damp-proof courses as well as for use in building man holes. Stronger and less porous engineering bricks, class B are usually red. Class B bricks have a strength greater than 75N/mm² and water absorption of less than 7%. Red class B Engineering bricks can also be used as a face brick to give a nice, clean, sharp edge finish to your wall.