Final answer:
Masonry walls without joint reinforcement are indeed called plain masonry walls, relying solely on material strength and craftsmanship. Ashlar masonry is an example of this practice.
Step-by-step explanation:
The statement that masonry walls without joint reinforcement are called plain masonry walls is true. Plain masonry is a term used to describe a construction technique where walls are made without the use of reinforcement, such as masonry nails or joint reinforcement. This type of masonry relies solely on the inherent strength of the materials and the skillful placement of these materials to ensure the stability and load-bearing capacity of the wall. An example of this is ashlar masonry, which is a stone construction style where stones are precisely cut and set in a pattern to form a stable structure with little to no mortar. Given that the stability of the wall systems is critical especially in supporting roof structures, the capacity of plain masonry walls to support large roofs and hence larger openings is limited to prevent structural failure.