Fabric: a woven cloth or material of organic or inorganic filaments, threads or yarns used for reinforcement in certain membranes and flashings.
Factory Mutual research (FMR): commonly referred to as "FM" a research and testing organization that classifies roofing components and assemblies for their fire, traffic, impact (hail), weathering, and wind-uplift resistance for four major insurance companies in the United States.
Fiberglass mat: fibers condensed into strong, resilient mats for use in roofing materials.
Field of the roof: refers to the central part of a roof away from the perimeter.
Film: a membrane or sheeting material with a nominal thickness of 10 mils or less.
Film thickness: the thickness of a membrane or coating that is expressed in mils (thousandths of an inch). See Wet film thickness and Dry film thickness.
Fine mineral-surfacing: a fine mineral material on the surface of roofing materials to prevent them from sticking to surfaces. 50% of this material has to pass through a sieve with holes that are 1/35" in size (#35 sieve).
Fishmouth: an opening along the exposed edge of an installed ply of felt caused by shifting the ply during installation. Repair these by making a slice along their entire length and feathering two plies of felt over the fishmouth for a minimum coverage of one foot all the way around.
Flaking: occurs when a coating loses it cohesion.
Flange: a projection edge of a roof component such as flashings, skylight frames, pre-manufactured curbs, etc. Usually refers to the part that sits on the roof surface.
Flash: to install flashing components.
Flash point: the lowest temperature of a liquid material at which combustion will occur when air reaches its surface.
Flashing: components used to seal the roof systems at areas where the roof covering is interrupted or terminated. For example, pipes, curbs, walls, etc. all have special components that, when correctly installed, will help prevent moisture entry into the roof system or building.
Flashing cement: a trowelable mixture of solvent-based bitumen and mineral stabilizers.
Flood (pour) coat: the surfacing layer of bitumen into which surfacing aggregate is embedded on an aggregate-surfaced built-up roof.
Flood test: the procedure in which a controlled amount of water is temporarily retained over a horizontal surface to determine the effectiveness of the waterproofing system.
Fluid-applied elastomer: a liquid elastomeric material that cures after application to form a continuous waterproofing membrane.
FM: see Factory Mutual research (FMR).
Froth pack: a term used to describe small, disposable aerosol cans that contain SPF components. Two component froth packs are available to do small repairs for sprayed polyurethane foam-based roofs.