Picture framing. Rectangular membrane ridging forming over
insulation board joints, found predominantly in smooth-surfaced
Pitch pocket. Flanged, open-bottomed metal container placed
around a column or other roof-penetrating element and filled with
bitumen or plastic cement to seal the opening.
Plastic cement. Trowelable, plastic mixture of bitumen and
asbestos (or other inorganic) stabilizing fibers and a solvent,
used mainly for horizontal surfaces as opposed to Flashing
cement, which is designed for vertical surfaces requiring sag-
Plasticizer. High-boiling-point solvent or softening agent added
to a polymer to facilitate processing or to increase flexibility
or toughness in the manufactured material.
Ply. A layer of felt in a roof membrane; a four-ply membrane has
at least four plies of felt at any vertical cross section cut
through the membrane.
Polymer. Long-chain macromolecules produced from monomers, for
the purpose of increasing tensile strength of sheets used as
membranes or flashing.
Polyvinyl chloride (PVC). A thermoplastic polymer, formulated
with a plasticizer, used as a single-ply sheet membrane material.
Power-trowel. Term applied to finish of a structural concrete
deck slab's surface by a power-driven steel-troweling machine.
Primer. Thin liquid applied to seal a surface, to absorb dust,
and to promote adhesion of subsequently applied material.
Protected membrane roof (PMR). A roof assembly with insulation
atop the membrane instead of vice versa, as in the conventional
roof assembly. (Also known as an inverted or upside-down roof
Psychrometric chart. A graphical representation of the
properties of moist air, usually including wet and dry bulb
temperatures, specific and relative humidities, enthalpy, and