Final answer:
The first course of block is laid on a bed of mortar, which is a mix of lime, sand, and water used to bond bricks or stones to the footing.
Step-by-step explanation:
The first course of block is laid on top of a bed of mortar which is placed on top of the footing. Mortar is a material used in masonry construction that serves as a bonding agent between bricks and stones.
It typically consists of a mix of lime, sand, and water, and sometimes includes cement as well.
This mixture is crucial because it not only adheres the stone or brick to the footing but also accommodates irregularities in the bed of the construction surface.
The use of mortar dates back to ancient times, with the Romans significantly improving its composition by adding volcanic sand known as 'pozzolana', resulting in a mortar that was strong and durable.