What is the thin mortar-like material that is poured into walls for reinforcement called?

The thin mortar-like material that is poured into walls for reinforcement is called grout. Grout is a mixture of water, cement, and sometimes sand or other additives, designed specifically to fill gaps and provide support. In masonry, it is commonly used in concrete block walls to improve structural integrity and bond the blocks together. When poured into the voids of masonry units, grout not only adds strength but also helps to hold the units in place.

This material is particularly effective because it can flow easily into tight spaces and bonds well with the surrounding masonry, creating a durable and stable structure. Unlike cement, which is a binder used in making concrete, and concrete itself, which is a composite material made of cement, aggregates, and water, grout serves a specific role in enhancing the strength of masonry walls. Plaster, on the other hand, is typically used for finishing surfaces rather than structural reinforcement.