These thin blocks, usually 60 or 75 mm thick, are made with the same lightweight aggregate as those in Class 2. These blocks are more expensive than dense aggregate blocks and are used principally for non-loadbearing partitions. These blocks are manufactured as solid, hollow or cellular depending largely on the thickness of the block.
The thin blocks are solid and either square edged or with a tongue and groove in the short edges so that there is a mechanical bond between blocks to improve the stability of internal partitions. The poor structural stability may be improved by the use of storey height door linings which are secured at floor and ceiling level.
Thin block internal partitions afford negligible acoustic insulation and poor support for fittings, such as book shelves secured to them.
The thicker blocks are either hollow or cellular to reduce weight and drying shrinkage.