Absorption: the ability of a material to accept within its body quantities of gases or liquid, such as moisture.
Accelerated Weathering: the process in which materials are exposed to a controlled environment where various exposures such as heat, water, condensation, or light are altered to magnify their effects, thereby accelerating the weathering process. The material’s physical properties are measured after this process and compared to the original properties of the unexposed material, or to the properties of the material that has been exposed to natural weathering.
Adhere: to cause two surfaces to be held together by adhesion, typically with asphalt or roofing cements in built-up roofing and with contact cements in some single-ply membranes.
Aggregate: rock, stone, crushed stone, crushed slag, water-worn gravel or marble chips used for surfacing and/or ballasting a roof system.
Aging: the effect on materials that are exposed to an environment for an interval of time.
Alligatoring: the cracking of the surfacing bitumen on a built-up roof, producing a pattern of cracks similar to an alligator’s hide; the cracks may or may not extend through the surfacing bitumen.
Aluminum: a non-rusting metal sometimes used for metal roofing and flashing.
