Term Description
Pinhole

A tiny hole in a coating, film, foil, membrane or laminate comparable in size to one made by a pin.
Pitch

See ‚"coal tar.‚"

Pitch-pocket (pitch-pan)

A flanged, open-bottomed enclosure made of sheet metal or other material placed around a penetration through the roof, properly stripped-in to the roof membrane and filled with grout and bituminous or polymeric sealants to seal the area around the penetration.
Plastic cement

A roofing industry generic term used to describe asphalt roof cement that is a trowelable mixture of solvent-based bitumen, mineral stabilizers, and other fibers and/or fillers; generally it is intended for use on relatively low slopes, not vertical surfaces. See "asphalt roof cement" and "flashing cement."
Plasticizer

A material incorporated into another material to increase its ease of workability, flexibility or distensibility.
Plasticizer migration

In some thermoplastic roof membranes, the loss of plasticizer chemicals from the membrane resulting in shrinkage and embrittlement of the membrane.
Pliability

The material property of being flexible or moldable.
Ply

A layer of felt or ply sheet in a built-up membrane roof or waterproofing system.
Plywood

A flat panel built up of sheets of wood called veneers, united under pressure by a bonding agent to create a panel with an adhesive bond between plies as strong as or stronger than the wood. Plywood is constructed of an odd number of layers with grain of adjacent layers perpendicular. Layers may consist of a single ply or two or more plies laminated with parallel grain direction. Outer layers and all odd-numbered layers generally have the grain direction oriented parallel to the long dimension of the panel.
PMMA

See ‚"Polymethyl methacrylate (PMMA).‚"
PMR

See "protected membrane roof (PMR)."
Polyester

A polymer in which the repeated structural unit in the chain is of the ester type.
Polyisobutylene (PIB)

A product formed by the polymerization of isobutylene; may be compounded for use as a roof membrane material.
Polyisocyanurate foam

A cellular, unfaced, preformed rigid thermal insulation produced by the polymerization of polyisocyanates in the presence of polyhydroxyl compounds, catalysts, cell stabilizers and blowing agents; classified in accordance with ASTM C591.
Polyisocyanurate foam board

A thermal insulation composed of polyisocyanurate foam with adhered facers; commonly called "iso" or "isoboard"; classified in accordance with ASTM C1289.
Polymer

A macromolecular material formed by the chemical combination of monomers having the same or different chemical composition.
Polymer-modified bitumen

(1) A bitumen modified by including one or more polymers (e.g., atactic polypropylene, styrene butadiene styrene); (2) composite sheets consisting of a polymer-modified bitumen often reinforced with various types of mats or films and sometimes surfaced with films, foils or mineral granules.
Polymeric methylene diphenyl diisocyanate (PMDI)

See "methylene diphenyl diisocynate (MDI)."
Polymerization

A chemical reaction in which monomers are linked together to form polymers.
Polymethyl methacrylate (PMMA)

A synthetic resin used in constructing liquid-applied roof membranes and flashings.
Polyol

A polyhydric alcohol (one containing three or more hydroxyl groups); the main ingredient of the resin component (B-component or B-side) of polyisocyanurate and polyurethane compounds. See "resin (1)."
Polypropylene

A polymer prepared by the polymerization of propylene as the sole monomer.
Polystyrene

A polymer prepared by the polymerization of styrene as the sole monomer.
Polyurethane

A polymer prepared by the reaction of an organic diisocyanate with compounds containing hydroxyl groups (polyols). Polyurethanes, or urethanes as they are sometimes called, may be thermosetting, thermoplastic, rigid or soft and flexible, cellular or solid; they can be aliphatic or aromatic. See "aliphatic polyurethane" and "aromatic polyurethane."
Polyurethane coating

A one- or two-part solvent-based coating that contains polyisocyanate monomer and a hydroxyl containing resin, that reacts during cure to form elastomeric coating.

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