There are many different types of adhesives available in the market. As substrates and conditions of the projects vary, it is imperative that you follow the instructions and advice of the tile merchant and strictly adhere to the instructions of the manufacturer.
The Australian Standards (3958.1) require that wall tiling in residential areas must have a minimum adhesive coverage of 65% for wet areas and external walls require a minimum of 90%.
Do not begin grouting for at least 16 hours after fixing unless you are using a fast set adhesive that allows grouting before this, and ensure that all joints are free of adhesive.
Source: Australian Tile Council website