: (B-component) One component of a two-component system. For polyurethane foam and coatings, the RESIN component. (See RESIN.) 

BACK ROLLING: Rolling a wet coating behind a spray or roller application to ensure better coverage on rough surfaces. 

BASE COAT: The first coat of a multi-coat system. This should be applied the same day as the SPF. 

BIO-CONTENT: Materials that are natural, non-petroleum based, and have harvest cycles of 10 years or less per LEED standards. Bio-content is determined by ASTM D 6866, whereby the percentage of new carbon atoms is measured in relationship to the percentage of old carbon atoms. All bio-content claims shall be based on the finished foam product and not the individual raw materials. (See also LEADERSHIP IN ENERGY AND ENVIRONMENTAL DESIGN [LEED].)

BIRDBATH: Random, inconsequential amounts of residual water on a roof membrane. 

BITUMEN: A class of amorphous, dark brown to black (solid, semi-solid, or viscous), high molecular weight hydrocarbons derived from petroleum refining or coal reduction. (See ASPHALT; COAL TAR.)

BLEEDING: (1) The diffusion of coloring matter through a coating from its substrate (such as bleeding of asphalt mastic through coating). (2) The absorption of oil or vehicle from a compound into an adjacent porous surface. 

BLISTER: An uplifting of coating or polyurethane foam caused by an enclosed pocket of gas or liquid entrapped between coating passes, foam and coating, foam and substrate, or within the foam itself. Caused by the DELAMINATION of one or two components in an insulation or roofing system. (See DELAMINATION.)

BLOWHOLE: A hole in the polyurethane foam surface and/or coating surface about 1 mm in diameter (the size of a ballpoint pen tip). (See also PINHOLE.)

BLOWING AGENT: A chemical additive formulated into either the A-side or B-side of the system, which creates bubbles that are trapped in the polyurethane as it solidifies to form foam cells. The gas produced from the blowing agent contributes to more than 97% of the volume of polyurethane foam. The blowing agent can be physical or reactive in nature. The physical blowing agents (e.g., liquid fluorocarbon) vaporize with the heat of the polyurethane reaction. The reactive blowing agents (e.g., water) react with one of the other chemicals in the formulation to produce a gas during the reaction (e.g., water and isocyanate yields carbon dioxide).

BOARD-FOOT: A volume measurement of materials such as SPF insulation, board-stock insulation, and lumber. One board-foot equals a volume of 12 in. by 12 in. by 1 in. Abbreviated bd•ft (1 bd•ft = 1/12 cubic ft = 0.00236 m3).

BOCA: Acronym for Building Officials Code Administrators International. BOCA, once one of three model code agencies in the United States, developed the National Building Code which had been commonly adopted in the Eastern and Midwestern U.S. BOCA has been absorbed into the ICC. (See also INTERNATIONAL CODE COUNCIL.)

BOND, CHEMICAL: Adhesion between surfaces, usually of similar materials, resulting from a chemical reaction or cross-linking of polymer chains. 

BOND, MECHANICAL: Adhesion between surfaces resulting from interfacial forces or a physical interlocking. 

BUILDING CODE: A set of rules that establish the minimum acceptable levels of safety for constructed structures. Building codes also provide minimum standards for the energy consumption of structures. In the United States, model codes are developed and published by the INTERNATIONAL CODE COUNCIL (ICC) and the NATIONAL FIRE PROTECTION ASSOCIATION (NFPA). Model codes acquire legal standing when adopted by state or local authorities. (See INTERNATIONAL CODE COUNCIL; NATIONAL FIRE PROTECTION ASSOCIATION [NFPA].)

BUILDING ENVELOPE: The exterior shell of the building, which provides structural integrity and control of heat, air, and moisture. 

BUILDING SCIENCE: Involves the application of basic science knowledge and analysis procedures to the design of buildings. There is special knowledge and experience required, and such expertise is also beneficial in determining how to correct problems in existing buildings and to explain what went wrong in the event of problems. 

BUILT-UP ROOF (BUR): A roofing membrane consisting of alternating applications of bituminous impregnated felts (or fabrics) and hot (or cold) mopped bitumen. The membrane is generally surfaced with aggregate. 

BUTYL COATING: An elastomeric coating system derived from polymerized isobutylene. Butyl coatings are characterized by low water vapor permeability.

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