In structural masonry, however, there is no framing, and the courses of units are laid precisely according to the architectural plan. Different types of concrete or ceramic units fulfill specific functions in each project, and they are normally bonded together with cement mortar. Plumbing and electrical systems are normally installed by cutting chases on the finished walls, which is a very inefficient construction process of building up an entire wall only to open it up again for pipes and conduits. This envelope has the sole purpose of enclosing the building and providing thermal and acoustic comfort. After the concrete sets, the molds are removed leaving a structural skeleton, which is then complemented with walls that can be made of many different materials. Tradicional column-beam systems use timber formwork built on-site according to the architectural project, forming molds into which steel reinforcement is added and concrete or similar materials are poured.