Blocks should not be tapped excessively, or at all if possible, to align them, as this tends to make them lose adhesion with the mortar bed. This is particularly the case with aerated concrete blocks, which have a higher suction rate and tend to dry out the mortar bed quite quickly.
Instead, try to squeeze the blocks into position, which means avoiding spreading joints that are too thick. A common mistake made by many people who are new to bricklaying is to assume that, because a block is big, the mortar joints should also be big. This is simply not the case. When laying blocks, bed joints and cross-joints are 10mm, as they are for brickwork. The size of blocks has been designed to complement bricks, with one course of blocks being the same height/gauge as three courses of brickwork and one block being the same length as two bricks with a 10mm cross-joint in between (Fig 144).
Fig. 144 Size comparison between bricks and 100mm blocks.
When laying aerated concrete blocks for fair-faced work, be careful not to damage arrises during handling and laying. Aerated blocks break easily if dropped and carelessly trimming off mortar with the trowel when spreading bed joints can easily cut the edge of a block. Similarly, the block face is easily damaged when adjusting the block to position by careless use of the edge of the trowel blade.