Flint-lime bricks are manufactured from hydrated lime and crushed
flint and are moulded and hardened as are sand-lime bricks. They are identical with sand-lime bricks in all respects.
Cellular and perforated bricks, illustrated in Fig. 48, are machine press moulded from plastic clays, either pressed from wire cuts or separately formed. The purpose of forming the hollows and perforations is to reduce the volume of moulded, wet clay, the better to control shrinkage and deformation during drying and burning to produce more uniformly shaped bricks.
These bricks, which have good crushing strength and are of semi-engineering quality, are used extensively in the brick enclosures to inspection pits and chambers for underground cable, for foundations and basements where the uniform shape and the density of the brick is an advantage.
They may be used for external walls as the perforations and hollows do not affect the weathering properties of the wall and may provide some little increase in insulation.