ACETONE
A ketone group solvent that is used to dissolve polyester resins. Used to a large extent for clean up of tools in fiberglass operations.

ADDITIVE
Any number of materials used to modify the properties of polymer resins. Categories of additives include reagents, fillers, viscosity modifiers pigments and others.

ALLIGATORING
A visible cosmetic defect in the exposed gel coat which looks like wrinkled or alligator skin.

ANTIMONY TRIOXIDE
Fire retardant additive for use with resins.

BARCOL HARDNESS
A measure of surface hardness made with a Barcol Impressor instrument in accordance with ASTM D-2583. The hardness value can be used as an indication of the degree of cure of FRP laminates.

BARRIER CREAM
A cream used to protect the skin from contact with resins.

BENZOYL PEROXIDE (BPO)
One of two generally used initiators for curing polyester resin. BPO is used with aniline accelerators or where heat is used to cure the resin. See MEKP.

BI-DIRECTIONAL
Reinforcing fibers that are arranged in two directions, usually at right angles

BINDER
A resin soluble adhesive that secures the random fibers in chopped strand mat or continuous strand roving.

BLISTER
A flaw either between layers of laminate or between the gel coat film and laminate.

CATALYST
Technically considered an initiator, catalyst is the colloquial name given to the substance added to the resin or gel coat in controlled quantities to initiate the cure.

CAULK
An elastic material used to protect joints or connections from external elements, particularly moisture.

CAVITY
The space between a male and female mold set in which the part is formed. Sometimes used to refer to a female mold.

CENTIPOSE
A unit of measure used to describe the viscosity of a liquid. The centipoise of a resin is measured with a Brookfield Viscometer for most polyester resin applications.

CHALKING
A surface phenomenon indicating degradation of a cosmetic surface. Chalking is a powdery film which appears lighter than the original color.

CHOPPED STRAND MAT
A fiberglass reinforcement consisting short strands of fiber arranged in a random pattern and held together with a binder. Mat is generally used in rolls consisting of 3/4 oz/ft2 material to 2 oz/ft2 material.

CLOTH
A fiberglass reinforcement made by weaving strands of glass fiber yarns. Cloth is available in various weights measured in ounces per square yard or Kg/m2

COMPOSITE
A chemical or mechanical bonding of dissimilar materials such as glass fiber and polyester resin, whose cumulative properties are superior to the individual materials.

COMPRESSION MOLD
A closed mold, usually of steel, used to form a composite under heat and pressure

COMPRESSIVE MODULUS
A mechanical property description which measures the compression of a sample at a specified load. Described in ASTM D-695.

COMPRESSIVE STRENGTH
The stress a given material can withstand when compressed.

CONNECTION
Where two panels are attached to each other or a panel is attached to the building.

CONTACT MOLDING
Refers to the use of a single or open mold onto which layers of polymer and reinforcement materials can be applied. Contact molding is characterized by one finished cosmetic side.

CONTINOUS FILAMENT STRAND
An individual rod of glass with small diameter, flexibility and great or indefinite strength. Also when referring to gun roving, is a collection of string like glass fiber or yarn, which is fed through a chopper gun in the spray up process.

CONTINUOUS STRAND ROVING
A bundle of glass filaments which are fed through a chopper gun in the spray up process.

CONTINUOUS LAMINATING
A process for forming panels and sheeting in which fabric or mat is passed through a resin bath, brought together between covering sheets, and passed through a heating zone for cure. Squeeze rolls control thickness and resin content as the various plies are brought together.

CORE
A low density material used between two FRP skins. Examples of core materials are end-grain balsa wood, urethane foam, PVC foam and various honeycomb materials.

CRAZING
Cracking of gel coat or resin due to stress.

CROSS-LINKING
The chemical bonding of molecules which in polymers occurs in the curing transition from a liquid to a solid.

CURE
The completion of the cross-linking process during which a composite develops its full strength.

CURE TIME
Time between introduction of catalyst or initiator to a polymer and final cure.

DENSITY
A comparison of weight per volume, measured in pounds per cubic foot.

DIELECTRIC STRENGTH
The value of a material as an electrical insulator or the resistance to the flow of electric current.

DIMENSIONAL STABILITY
A description of the change in size of an object during the molding process or in varying temperature conditions or under various loads.

DISTORTION
A change in shape form that which is intended. It is symptomatic of laminating difficulties, curing problems, tooling problems or resin shrinkage.

DRAFT
The angle of the vertical components of a mold which allow removal of the part.

ELONGATION
Standard measure for the amount a sample can stretch as a percentage of original length before it fails or breaks.

ENCAPSULATING
Completely surrounding an object with resin or a fiber resin composite.

EPOXY RESIN
A polymer resin characterized by epoxide molecule groups. Epoxies generally have higher physical properties than polyester resins. They are also more costly and difficult to process and less able to endure exposure to sunlight.

EXOTHERMIC HEAT
Internally developed heat accompanying a chemical reaction, such as might be created when curing a thermosetting resin.

FEMALE MOLD
A concave mold used to precisely define the convex surface of a molded part.

FIBER
Reinforcement material which is a major component in a composite matrix.

FIBERGLASS
Glass which has been extruded into extremely fine filaments. These filaments vary in diameter, and are measured in microns. Glass filaments are treated with special binders and processed similar to textile fibers. These fibers come in many forms such as roving, woven roving, mat and continuous strands.

FILAMENT
A single thread-like fiber of extruded glass. Typically microns in diameter.

FILAMENT WINDING
A process which involves winding a resin-saturated strand of glass filament around a rotating mandrel.

FILLERS
Usually inert organic or inorganic materials which are added to plastics, resins or gel coats to vary the properties, extend volume, or lower the cost of the article being produced.

FIRE RETARDANTS
Compounds mixed with the resin to reduce flammability.

FISH EYE
The effect of surface contamination which causes a circular separation of a paint or gel coat.

FLAME RETARDANT RESIN
A polyester resin which has been specifically formulated to reduce the flame spread and/or smoke generation characteristics.

FLAMMABILITY
A measure of how fast a material will burn under controlled conditions. ASTM D-635/UL E-84 tests.

FLANGE
An extension around the perimeter of a mold or part for the purpose of demolding, stiffening or connecting two components.

FLASH POINT
The lowest temperature at which a substance gives off enough vapors to form a flammable mixture.

FLEXURAL MODULUS
ASTM D-790. An engineering measurement which determines how much a sample will bend when a given load is applied.

FOAM
A lightweight, cellular plastic material containing gas-filled voids. Typical foams include urethane, PVC and polyester.

FOAM-IN-PLACE
The process of creating a foam by the combination of two liquid polymers. See IN-SITU.

FRP
Fiber Reinforced Plastics, also known as GFRP (Glass Fiber Reinforced Plastic), GRP (Glass Reinforced Plastic) and RP (Reinforced Plastic).

GEL-COAT
A surface coat of a specialized polyester resin, either colored or clear, providing a cosmetic enhancement and weatherability to a fiberglass laminate.

GEL TIME
The length of time from catalyzation to gel or "B" stage.

GELATION
The formation of a gel.

GOOD SIDE
The side of a molding in contact with a mold surface.

GREEN
Resin which has not completely cured and is still rather soft and rubbery.

GRP
Glass reinforced plastics. Generally based on polyester resin. See FIBERGLASS, FRP.

HEAT DISTORTION POINT
The temperature at which the strength of a material begins to degrade.

HET-ACID RESIN
Polyester resin with exceptional fire qualities.

HONEYCOMB CORE
Strips of paper, plastic, metal, etc., joined together to form a honeycomb pattern. Used as a lightweight core in sandwich moldings.

INHIBITOR
An additive to polyester resin or styrene used to slow the chemical reaction which leads to curing.

INSERT
A piece of material put into a laminate during or before molding to serve a definite purpose.

INTUMESCENT
A fire-retardant technology which causes an otherwise flammable material to foam, forming an insulating barrier when exposed to heat.

IN-SITU
In the position which it will finally occupy, e.g. molding or forming foam.

ISOPHTHALIC
A polyester resin based on isophthalic acid, generally higher in properties than a general purpose or orthothatic polyester resin.

ISOTROPIC
The description of equal strength properties in all orientation. Isoptropic composites are usually achieved by random fiber orientation.

JIG
Any fixture for holding parts in position, while joining them together or to maintain their shape.

JOINT
A line or distinction formed when two panels are connected. Also referred to as a seam.

LAMINATE
To place into a mold a series of layers of polymer and reinforcement. The act of applying FRP materials to a mold. To lay up.

LAMINATION
Applying layers of glass and resin to a mold. Also used to describe a single ply of laminate.

LAYER
A single ply of lay up or laminate.

LAY UP
The act of building up successive layers of polymer and reinforcement. Layers of catalyzed resin and fiberglass or other reinforcements are applied to a mold in order to make a part.

LOW-PRESSURE LAMINATES
Laminated molded and cured using pressures from 400 psi down to and including the pressure obtained by mere contact of the plies.

MASTER
A full scale representation of the intended part, usually retained as a reference and the part from which production molds are made.

MAT
See CHOPPED STRAND MAT.

MATCHED DIE MOLDING
Technique for producing long runs of identical parts with two finished sides.

MATCHED MOLDS
Two or more tools arranged in a set as a male and female mold. Normally used in a press.

MATRIX
The liquid component of a composite or laminate.

MEK PEROXIDE (MEKP)
One of two initiators often referred to as catalyst and used to initiate polymerization of a resin. Methyl Ethyl Ketone Peroxide. (See BENZOYL PEROXIDE).

MEK SOLVENT
Methyl Ethyl Ketone; a colorless, flammable liquid sometimes used in clean up procedures.

MICROBALLOONS
Microscopic bubbles of glass, ceramic or phenolic, used as a filler or to create syntactic foam or putty mixtures.

MIL (MIL THICKNESS)
The unit used in measuring film thickness. One mil equals one thousandth of an inch. (1 mil = .001 ").

MILLED FIBERS
Glass fiber processed by a hammer mill into lengths of 1/32" to 1/8". Commonly used as a reinforcement in polyester putty.

MODULUS OF ELASTICITY
An engineering term used to describe a material's ability to bend without losing its ability to return to its original physical properties.

MOLD
The tool used to fabricate the desired part shape. Also used to describe the process of making a part in a mold.

MOLDING
The process of using a mold to form a part.

MOLD RELEASE
A wax or polymer compound that is applied to the mold surface which acts as a barrier between the mold and the part, thus preventing the part from bonding to the mold.

MONOMER
One of the constituents of polyester resin.

NON-AIR-INHIBITED RESIN
A resin in which the surface cure will not be inhibited or stopped by the presence of air.

ORTHOPHTHALIC RESIN ORTHO
A polyester resin based on orthophthalic acid, also known as a general purpose resin (GP).

PARTING LINE
The location on a molded product between different segments of the mold used to produce the product.

PATTERN
The initial model for making fiberglass molds. See PLUG.

PIGMENT
A colorant added to gel coat or resin.

PIGMENT SEPARATION
Occurs when the pigment is not thoroughly mixed into the gel coat during formulation or the gel coat is improperly mixed prior to use. It is characterized by a nonhomogeneous surface color.

PINHOLES
Small holes on the exposed gel coated surface. They are about the diameter of common pins and may be easily counted.

PLASTICS
Organic chemical compounds called polymers which can be formulated to produce a wide range of properties.

PLUG
A composite industry name for a pattern or model.

POLYESTER (unsaturated)
The product of an acid-glycol reaction commonly blended with a monomer to create a polymer resin. In its thermosetting form it is the most common resin used in the FRP industry.

POLYMER
A chain molecule composed of many identical groups, commonly found in plastics.

POLYMERIZATION
The chemical bonding of polymer molecules during the curing reaction.

POLYVINYL ALCOHOL (PVA)
A parting film applied to a mold for part releasing.

POROSITY
Entrapped gas bubbles or voids in a gel coat film.

POST-CURE
To cure by application of heat after the chemical exothermic reaction has subsided.

POT LIFE
The time during which the catalyzed resin remains liquid or "workable." See GEL TIME.

PREMIX
Reinforcing material mixed with resin, and usually with pigment, filler and catalyst, before placing in the mold.

PREPREG
Reinforcing material impregnated with resin prior to the molding process and cured by the application of heat.

PRESSURE BAG
A membrane which conforms to the inside of a laminate laid up on a mold. The membrane or bag is then inflated applying pressure which consolidates and densifies the laminate.

PRINT THROUGH
A distortion in the surface of a part which allows the pattern of the core or fiberglass reinforcement to be visible through the surface. Also known as print out, telegraphing or read through.

PROMOTER
A reagent which speeds resin cure. See ACCELERATOR.

PUTTY
A thickened mixture of resin made by adding fillers, thixotrophs and reinforcing fibers.

PVA
See POLYVINYL ALCOHOL.

REINFORCEMENT
A fiber which when encapsulated in a polymer resin matrix forms a composite or fiberglass laminate. Also refers to a structural member designed to stiffen a molded part.

RELEASE AGENT
A compound used to reduce surface tension or adhesion between a mold and a part.

RESIN
A liquid polymer which when catalyzed cures to a solid state.

RESIN TEARING
Separation of pigments in a gel coat affecting cosmetic appearance.

ROVING
A collection of bundles of continuous filaments in untwisted strands. Used in the spray-up (chopping) process.

SEAM
See JOINT.

SELF EXTINGUISHING
Ceases to burn when the source of flame is removed.

SELF-TAPPING SCREWS
Hardened screws which cut their own thread as they are set.

SHEAR
An engineering term referring to forces applied normal to the surface of a given material. The movement between plies of a laminate is referred to as interlaminate shear.

SHELF LIFE
The allowable storage time before a product must be used.

SHIP LAP
Method of joining two panels together by means of one panel having a recessed shelf to receive the other panel on top of it leaving a flush surface.

SKIN COAT
The first layer of laminate next to the gel coat, generally, one ply of chopped strand mat.

SPECIFIC GRAVITY
The ratio between the density of a given substance and the density of water.

SPLIT MOLD
An open mold made in two or more pieces.

SPRAY UP
The process of spraying glass fibers, resin and catalyst simultaneously into a mold using a chopper gun.

STYRENE MONOMER
A component of polyester resin that provides crosslinking sites and reduces the polyester to a workable viscosity.

SURFACE MAT
A lightweight tissue (10-30 mils thick) of glass or synthetic fiber used to provide a resin-rich surface. See VEIL.

SURFACTANT
Chemicals used to modify or change the surface of a layer of resin or polymer. Usually used to form a film on a curing resin, producing a tack-free surface.

SYNTACTIC FOAM
A foam made by mixing microspheres with a resin.

TACK FREE
A surface which is not sticky after cure.

TAPE
A narrow width reinforcing fabric or mat.

TENSILE LOAD
A load applied away from and to opposite ends of a given sample.

TENSILE ELONGATION
An engineering term referring to the amount of stretch a sample experiences during tensile strain. ASTM D-638.

TENSILE STRENGTH
A measurement of the tensile load a sample can withstand. ASTM D-638.

THERMAL COEFFICIENT OF EXPANSION
Measures dimensional change of a material when heated or cooled. Measured in inches per inch per degree.

THERMAL CONDUCTIVITY
Measures the transfer of heat through a material.

THERMOPLASTICS
A group of plastic materials that become elastic or melt when heated, and return to their rigid state at room temperature. Examples are PVC, ABS, polystrene, polycarbonates, nylon, etc.

THERMOSETS
Materials that undergo a chemical crosslinking reaction going from liquid to solid or semi-solid. This reaction is irreversible. Typical thermosets are polyesters, acrylics, epoxies, and phenolics.

THIXOTROPIC
A term describing the rehology (or characteristics) of a liquid that resists flowing or drainage during application.

THIXOTROPIC INDEX (T.I.)
A measure of thixotropy using a Brookfield Viscometer. The low speed viscosity divided by the high speed viscosity.

TOOLING GEL COAT
A gel coat formulated for mold surfaces.

TRANSLUCENT
Permits a percentage of light to pass but not optically clear like window glass.

UNIDIRECTIONAL
Strength lying mainly in one direction. A glass reinforcement in which the fiber is oriented in one direction.

UV STABILIZER
A chemical compound which improves resistance to degradation from ultraviolet radiation.

VISCOSITY
The liquid properties of a material. Resistance to flow.

VOID FREE
A molding containing no entrapped air cavities, blisters, or voids.

WAX
A compound used as a release agent. See RELEASE AGENT.

WETTING-OUT
The action of saturating a glass fabric with resin. Also a measure of the speed with which a fabric soaks up resin.

WOVEN ROVING FABRIC
Heavy fabrics woven from continuous filament in roving form. Usually in weights between 18-30 oz. per square yard.