There are two categories of lime used in mortars -- pure or fat lime which requires carbon dioxide from the air if it is to set, and hydraulic lime which hardens without CO₂. A mortar composed of fat lime is particularly suited to surface work, while one based on hydraulic lime is better suited for work within a mass of masonry. McLaughin provides descriptions of both types of lime-based mortars which were used in the restoration of buildings in Bath, England, and discusses the shortcomings of each mixture for the purpose to which it was applied.