(gravity wall), or using blocks (typically an architectural style of block or clad with a veneer such as brick) with a concrete base, steel reinforcing and mortar (piling wall). Other very common, non-structural uses for concrete block walls (especially in American schools) are as interior fire-rated and extremely durable partition walls, and as exterior backup curtain walls for attachment of building envelope systems (rigid foam insulation and an air/vapor barrier) and veneers (stucco, steel, brick, or split-face concrete block). Structural properties Concrete masonry walls may be ungrouted, partially grouted, or fully grouted, the latter two enhancing their structural strength. Additionally, steel reinforcement bars (rebar) can be used both vertically and horizontally inside a CMU wall to maximize its structural performance. The cells in which the rebar is placed must be grouted for the bars to bond to the wall. For this reason, high seismic zones typically only allow fully grouted walls in their building codes. The American design code that guides design engineers in using CMU as a structural system is the Masonry Standards Joint Committee's Building Code Requirements & Specification for Masonry Structures (TMS 402/ACI 530/ASCE 5). The compressive strength of concrete masonry units and masonry walls varies from approximately based on the type of concrete used to manufacture the unit, stacking orientation, the type of mortar used to build the wall, it depends on whether it is a load bearing partition or not and other factors. See also Concrete bricks Gypsum block Rusticated concrete block Fly ash brick References Sources External links How Products Are Made: Volume 3 Concrete Block Concrete Masonry Association of California and Nevada National Concrete Masonry Association Mason Contractors Association of America Concrete Block Association Masonry Institute of America "The History Behind Rock Face Block"—Classic Rock Face Block Masonry Soil-based building materials