Final answer:
Type N mortar is commonly used for exterior masonry veneer walls due to its balance of strength and durability. It has evolved from ancient mortars, like Roman concrete, to modern formulations that accommodate the environmental challenges faced by exterior walls.
Step-by-step explanation:
The mortar most commonly used in an exterior masonry veneer wall is type N mortar. This type of mortar mix, which is a blend of Portland cement, lime, and sand, provides a good balance of strength and durability, making it suitable for exterior applications where moderate structural needs are required as well as resistance to severe weather and high heat. In some cases, type S mortar may also be used when higher strength is needed.
Throughout history, mortar has evolved to meet the requirements of different construction technologies and styles. For instance, Roman concrete, as it was known in antiquity, was a significant advancement with the introduction of volcanic sand, or pozzolana, which made the mortar particularly strong and durable. Yet, the more modern type N mortar is designed to accommodate the thermal expansion and contraction and potential weather-related erosion that might occur to exterior walls.
In Romanesque architecture, the use of thick mortar beds was common to hold together the small, irregular pieces of building stone. However, in present-day exterior masonry veneer construction, the quality and consistency of mortar are tremendously important, and type N mortar is often chosen for its general-purpose use and good performance characteristics in a variety of environments.