Definitions (A-Z)

Note: All definitions located on this page are in alphabetical order. Definitions can be read by scrolling down on your web browser or by clicking the appropriate letter below.
Accelerator (resin): An additive that reduces gel and cure time of thermosetting plastics.
Acetone: A chemical solvent useful as a cleaner for FRP resins. It is very flammable.
Acrylic: The short chemical description for methyl methacrylate (MMA), a plastic that has hundreds of commercial applications. The base product is clear, and one of its major attributes is good resistance to ultraviolet light. Bathtubs and spas are commonly made from polymerized MMA, and is polymethyl methacrylate (PMMA). Acrylic sheet is thermoformed to create the desired shape.

There are three processes for manufacturing sheet; cell cast, continuous cast, and extruded. Each process yields a sheet with a different set of properties and cost. Continuous cast sheet is the preferred process for spas and bathtubs due to its outstanding balance of properties and economics. The product used in spas and bathtubs is cross-linked, which greatly improves chemical resistance and thermoformability. Extruded sheet is the cheapest, but it has a balance of properties that makes it perform at a lower level for bathtubs and spas. It cannot be produced as a cross-linked sheet. However, it might be adequate for some products, like shower walls.
Adhesive: A material that unites (bonds) two material surfaces.
Adhesive failure: A failure in an adhesive joint between the adhesive material and the adherend.
Adhesion Promoter: Material used to increase the adhesion of a topcoat or basecoat to its substrate.
Air Dry (Gel Coat or Resin): To cure at room temperature with addition of catalyst but without assistance of heat or pressure.
Air Dry (Coatings): It dries without addition of a catalyst or hardener. The evaporation of the solvent causes the coating to harden.
Alligatoring: A term used to describe wrinkling of gel coat film resembling alligator hide; caused by poor cure at time of contact with styrene from a subsequent or preceding coat.
Atmospheric Moisture: The atmosphere always contains some amount of water vapor which could have an effect on certain products when exposed or left open. For example polyurethane component “A” will crystallize. K2000 components can harden.

Atomize: The breaking-up of a coating into fine particles or droplets by a paint gun.

Baking: The process of applying heat to a coating to speed the cure or dry time.
Barcol Hardness: A measure of material hardness obtained by measuring the resistance to penetration by a sharp, steel point. It corresponds to the degree of cure in a gel coat or laminate.
Bare Substrate: Any material which does not have a coating of paint or primer.
Basecoat: A highly pigmented color which may require a coating of clear for protection, durability, and gloss.
Batch: Identity for all material produced during one operation possessing identical characteristics throughout.
Benzoyl Peroxide (BPO): Catalyst used in conjunction with aniline accelerators or where heat is used as an accelerator.
Bi-Directional: Arrangement of reinforcing fiber strands in which half the strands are laid at right angles to the other half. This produces equal strength in the two directions.
Binder (FRP): Bonding resin applied to glass fibers to hold them in position in a broadgoods textile structure. During lamination, this resin is dissolved by the styrene in polyester resin, and, if unsaturated, can become part of the final polymer network.
Bleeding (FRP): Result of softening of backside of gel coat (typically by laminating resin) which causes pigments to reflow.
Bleed Out: Excess liquid resin appearing at the surface.
Blending: The tapering of finishes or colors so slight differences cannot be distinguished. This is achieved by allowing some of the original finish to show through the new color.
Blistering: Effect of pressure from liquid or gas under a coating causing a swelling or large bubble in the finish. See Repair Definitions.
Blushing: A milky appearance of a topcoat caused by high humidity, causing water to condense on or in the coating.
Bond Strength: Stress required to separate a layer of material from another material that has been bonded together. Special tests, equipment, and procedures are available to determine the bond strength.
Brace: Integral structural element used to stiffen or strengthen a part.
Brittle: A coating lacking flexibility.
Bubbles: Air or solvent trapped on a paint film caused by poor atomization during spraying. Also, air trapped in repair filler caused by excessive agitation or heat.
Buffing/Compounding: Using a mild abrasive to increase gloss and/or remove texture in a coating.
Burn Through: Polishing or buffing of a color too hard or long causing the underlying coat”s) to be revealed or distortion of the surface.
Carbon (or Graphite) Fiber: Reinforcing fiber known for its light weight, high strength, and high stiffness..
Cast Polymer: Non-reinforced composite. It combines polymers, fillers and additives (w/o reinforcing fibers) to meet specific applications requirements.
Catalyst (resin): A substance that promotes or controls a chemical reaction (e.g. FRP cure) without being consumed. In the FRP industry, free radical initiators such as MEKP are often referred to as ‘catalyst’, but since it is consumed in the reaction, it is not a true scientific catalyst.
Catalyst Injection: Used withspray equipment to catalyze polyester at the spray gun, therefore eliminating the need to clean the system within the gel time of the polyester resin.
Catalyst (Peroxide): A substance added to a resin to make it gel and cure.
Centipoise (CPS): Unit of measure to designate a fluid’s viscosity.  At 70°F, water is one cps.
Chalking: Dry, powder-like appearance or deposit on exposed surface.
Chopped Strand: Uniform lengths of fibers formed by cutting continuous strand yarn or roving, usually from 1/32 to 2 inches long. Lengths up to 1/8” or called milled fibers
Chopped Strand Mat: Uniform lengths of fibers held together by binder and added to increase composite part glass skin thickness.
Closed Molding: A fabrication process in which a part is produced by injecting a resin in a cavity created by the combination of a female and male mold.
Cloth (Fiberglass): A fine weave of woven fiberglass.
Cobalt: A chemical element used as an accelerator for MEKP catalyzed polyesters
Coefficient of Thermal Expansion:  A material’s fractional change in dimension for a given unit change of temperature ( e.g. in./in/°F).
Cohesion: Tendency of a single substance to adhere to itself.
Cohesive Failure: Failure of an adhesive joint that occurs either within the adhesive material or within one or both adherends.
Color Match: When two colors exhibit no perceptible color difference when viewed under the same conditions (light, angle, etc.).
Color Retention: The ability of a color to retain its true shade over an extended period of time.
Color Standard: The “sample” created by the originator to define a specific color.  All other “samples” are measured in comparison to the one original.
Compressive Strength: The resistance to crushing or buckling force.
Concentration (Coatings): the ratio of pigments to base liquid.
Condensation Polymerization: Polymerization (creating large molecules from smaller ones) reaction in which simple by-products (e.g. water) are formed in addition to the primary polymer.
Contaminant: Impurity or foreign substance that effects one or more properties of the product.
Coploymer: Large chemical chain molecule composed of two or more dissimilar starting groups.
Core: Central component of a sandwich construction.
Cosmetic Stability: Capability of a substance or part to maintain appearance with respect to surface smoothness, color, gloss or other visual appearance characteristics.
Coverage: The ability of a pigmented color to conceal or cover a surface.
Crazing: Cracking due to internal stress.  See Repair Definitions.
Cross-linking:  A chemical process in which two adjacent long chain molecules are connected at the side.  This changes the physical and chemical properties of the polymer, substantially.
Cure: Polymerization or irreversible transformation from liquid to solid state with maximum physical properties.
Cure Temperature: Temperature at which material attains final cure.
Cure Time: Time required for liquid resin to reach majority of polymerized state after catalyst has been added.
Curing Agent: Catalytic or reactive agent that initiates polymerization when added to resin; also called ‘hardener’.
Delamination: Laminate defect that occurs due to mechanical, chemical or thermal stress and is characterized by separation between laminae.
Demold: To remove a part of its mold.
Density: Weight per unit volume (e.g.  pounds per cubic foot).
Diethylaniline (DEA): Accelerator used in conjunction with BPO catalyst, or as a promoter for cobalt/MEKP systems.
Diluent: Diluting (reducing or thinning)agent.
Dimethyaniline (DMA): Accelerator used in conjunction with BPO catalyst; but more effective than DEA.
Dimples: Small sunken dots in gel coat surface, generally caused by foreign particle, air void, or catalyst droplets in gel coat or laminate.
Dispersion:  A homogeneous mixture of suspended solid particles in liquid medium.
Distortion: Wavy gel coat surface reflection often found in conjunction with print-through.  It is commonly caused by problem in laminating system.
Drain Out: Leaking, sagging and puddling of laminating resin from reinforcement.
Dry Spot: Laminate defect that occurs during molding process and is characterized by dry, unwet fibers that have never been encapsulated by matrix material.
Durability: A measure of how well a product weathers and resists its environment.
E-Glass: The first type of glass used for fiber was soda lime glass or A glass. It is not very resistant to alkali. A new type, E-glass, was formed; this is an alumino-borosilicate glass that is alkali-free (<2%). This was the first glass formulation used for continuous filament formation. E-glass still makes up most of the glass fiber production in the world. Its particular components may differ slightly in percentage, but must fall within a specific range. The letter E is used because it was originally for electrical applications.
Elasticity: Capacity of materials to recover original size and shape after deformation.
Elastic Limit: Greatest stress material is capable of sustaining without permanent strain remaining after complete release of stress.
Elastomer: A polymeric material with the ability to recover its original shape and size at ambient temperature after removal of a deforming force.
Elongation: The increase in length when under tension.
Enamel: A coating which cures tack free.
Etch: The process of chemically treating the surface of a  material to improve the adhesion capability of a coating to be applied.
Exothermic Heat: Internally developed heat accompanying chemical reaction (e.g. curing)
Extenders: Low-cost materials used to dilute or extend higher-cost resins without excessive reduction in properties.
Fabric, Woven: A material constructed of interlaced yarns, fibers, or filaments.
Fabrication: Process of making something.
Fading:  Loss of color
Fatigue: Failure of material’s mechanical properties caused by repeated stress over time.
Feathering: Slang term for blending or slowly moving the edge of one color into a second color.
Fiber Content: Amount of fiber in a composite expressed as a ratio to the matrix by weight.
Fiber Orientation: Direction of fiber alignment in nonwoven or mat products.
Fiber Print: Cosmetic defect, visible on exterior gel coat surfaces that resemble fiber bundle.
Fiber Reinforced Plastics (FRP): General term for composite material or part that consists of plastic matrix containing reinforcing fibers such as glass or carbon having greater strength or stiffness than plastic.
Fiberglass: Fibers similar to wool or cotton fibers, but made from glass.  Glass fiber forms include cloth, yarn, mat, milled fibers, chopped strands, roving, and woven roving.
Fillers (resins): Relatively inert materials which are added to resins to impart special flow characteristics, to extend volume, and to lower cost.
Fillers (surface repair): A hardenable paste used to fill a voidpaste
Fish Eyes: Circular Separation in a coating generally caused by contamination.
Flash Point: Lowest temperature at which  a substance emits enough vapors to form flammable or ignitable mixture with air near the surface of the substance being tested.
Flattening Agent: An additive to paint or coating to reduce gloss.
Flooding: High delivery rate from spray gun.
Fracture: Rupture of surface of laminate due to external or internal forces; may or may not result in complete separation.
Free Radicals: A reactive molecular fragment capable of initiating a reaction.
FRP: Fiber Reinforced Polymers
Fumed Silica (Cab-o-Sil): Thickening agent or liquid resin filler to increase flow or reduce sag in polyester resins.
Gel: Resin that is partially cured.
Gel Coat: Surface coat, either colored or clear, providing cosmetic enhancement and protection for the laminate.
Gel Time: Length of time that catalyzed polyester remains workable after hardener is added.
Gelation: Transition of liquid to a soft solid.
Glaze: A very fine polishing material used to gain gloss and shine.
Gloss: Reflectance of light from a painted surface.  It is measured at different degrees by instruments known as gloss meters.
Grinding: Using a coarse abrasive to effect a surface.
Hand Layup: Laminating by hand rather than specialized equipment.
Heat: To increase temperature above ambient.
Hardener: Substance that reacts with resin to promote or control curing action.
Honeycomb: Manufactured sandwich product that has a core of hexagonal shell material.
Hot Pot: Catalyst is mixed with resin in a container prior to spraying.
Hybrid Resin: A resin with two or more chemistries combined.
Hydrophobic: Moisture resistant capability, moisture repelling.
Hygroscopic: Moisture absorbing capability.
Impregnate: Saturation of reinforcement with a resin.
Inhibitor: A substance used to slow or prevent a chemical reaction.
Injection Molding: To produce a part by injecting a resin into a mold under pressure.
Interface: The surface formed between two  combined adjacent materials.
Isotropic: Arrangement of reinforcing materials in random orientation, resulting in equal strength in all directions.
Laminate (verb):  Process by which a laminate is produced.
Lamination: Laying on of layers of reinforcing materials and resin, much like buildup of plywood.  Each layer is bonded to its adjacent layer.
Layup: Process of placing reinforcing material onto mold or surface and applying resin.
Mass: Quantity of matter
Master Mold: Durable, robust full-scale product used to produce multiple copies.
Mat: Fibrous reinforcing material composed of chopped filaments or swirled filaments with binder applied to maintain form; available in blankets of various widths, weights, thicknesses and lengths.
Matrix: Material in which fiber reinforcements of a composite structure is imbedded.
MEK Peroxide: Abbreviation for methyl ethyl ketone oeroxide;  it is the free radical source commonly used as initiator for polyester resins.
MEK (solvent): Methyl  ethyl  ketone.
Micro Cracking: Cracks formed in composites when thermal stresses locally exceed strength of matrix.
Mil: .001 inches
Milled Fibers: Fibers  which are hammer-milled into lengths from 1/32” to ¼”.
Mold: To shape a product (generally using heat and pressure).
Mold Coat: A coat of resin over a bare mold. It is used to seal mold and make a smooth surface.
Mold (Open-Close method): Process which utilizes a multiple-piece mold that can be opened for injection/insertion of molding material before closing to complete the part production process.
Mold Release: A substance used on a mold or in the compound to prevent sticking and to facilitate part release.
Molding: Forming of a part by various means, such as contact, pressure, matched die and continuous laminating, into a given shape.
Monomer: A partially polymerized organic chemical.
Neat Resin Application: Pure resin (promoted to cure) applied without fillers, reinforcement or flame retardants.
Orange Peel: A coated surface taking on the appearance of an orange peel ( rough wavy texture).
Original Equipment Manufacturer (OEM): Companies that design and build products bearing their name.
Out-Gassing: Release of solvents, volatiles, gasses, and moisture from composite parts.
Peroxides: Organic chemical compounds containing the O-O or O-OH group; used in oxidation reactions.
Pigment: Ingredient used to impart color.
Pigment Separation: Mottled (varied color) appearance.
Pinholes: Small air bubbles in a coating.  Unlike porosity, there are few enough to easily count.
Plastics: High molecular weight thermoplastic or thermosetting polymers that can be molded, cast, extruded or laminated into objects. Thermoplastic describes products that can undergo these processes multiple times.  Thermoset refers to materials which allow these processes to onl y be used once.
Plug: Term used for a master mold model crafted from variety of materials.  It is used to produce a mold for production use.
Polyester (unsaturated):  Resin formed by reaction between dibasic acids and dihydroxy alcohols, one of which must be unsaturated to permit cross-linking.
Polymer: A large chain organic molecule composed of repeating identical atomic groups.
Polymerization: The process of creating a polymer from the starting organic chemicals.
Polyvinyl alcohol: An organic chemical often used as a water soluble release agent.
Porosity: Small air bubbles in a surface; too numerous to count.
Postcure: Exposure of incompletely cured resin to higher temperatures to achieve more complete cure.
Pot Life: Same as Gel Time.
PrePreg: Resin-impregnated cloth, mat or filaments in flat form that can be stored for later use.
Preheating: Heating occurring prior to the primary process.
Premix: Mixture of resin, pigment, filler and catalyst.
Pre-release: Premature release of gel coat or laminate from the mold.
Primary Laminate: The “bulk” or secondary laminate, which is applied after the skin coat (first layer) has cured.
Print-through: Transfer of image of glass strands through the gel coat film.
Production Mold: Durable mold used for production of many parts.
Promoter: Same as Accelerator.
Reinforcement: Strong, relatively inert material used in a composite part to improve strength, stiffness, and impact resistance.
Release Agent: Same as Mold Release.
Release Film: Impermeable film layer that does not bond to composite during cure.
Resin: Any of a class of natural or synthetic polymers, solubilized or semi-soliid; generally of high molecular weight.
Resin Rich: A localized area filled with excess resin when compared to the goal resin to fiber ratio.
Resin Starved: The opposite of Resin Rich.
Sags/Runs: Sag is slumping of gel coat or resin film.  Run is running of same.
Sandwich Layup: A laminate composed of two outside layers of reinforced material with a weaker core material sandwiched between them in order to provide the I-beam effect of stiffening.
Set: To convert resin into a fixed or hardened state.
Shear: Stress caused by two contiguous parts or surfaces sliding in parallel direction to their plane of contact.
Shelf-life: Length of time chemicals can be stored before they become unusable for their intended purpose.
Sizing: Water-soluble solution of chemical additives used to coat filaments to impart specific properties.
Skin Laminate:  Thin, glass laminate applied directly against top surface layer to provide durability and other properties.
Sprayup: Process in which glass fibers, resin and catalyst are simultaneously deposited in or on mold.  This is accomplished with equipment similar to paint spraying.
Stiffness: Structural property that quantifies the relationship between force and moments applied to an object, and stretching or bending that occurs as a result of the force.
Strain: Deformation caused by stress.
Stress Crack: External or internal cracks in a coating or composite caused by tensile stresses. Some chemicals are known to accelerate stress cracking.  It can also be caused by overexposure to elevated temperatures or cyclic temperature variations.
Substrate: Material on which adhesive-containing substance is spread for any purpose.
Surface Profile: Cosmetic quality of surface.
Surfacing Agent: Material that allows surface of polyesters to cure; limits adhesion of another coat of resin if first coat is thoroughly cured.
Surfacing Veil: Used with other reinforcing mats and fabrics to enhance quality of surface finish.
Tack: Stickiness
Tensile Strength: Maximum stress a material can withstand before failure in a tension test.
Thermal Conductivity: A measure of a material’s ability to conduct heat.
Thermal Shock: Occurs when there is a rapid change in temperature. An example is in a bathtub drain area when the water from the faucet instantly changes from cold to very hot. These sudden changes can cause failures in the material around the drain.
Thermal Stress: Occurs when temperature changes would cause a material to expand/contract, but it can't change dimensions due to being restrained. For example, composite (layered) materials expand and contract differently with the same temperature change. Acrylics will expand about 4 times more than carbon steel with the same temperature change.
Thermoplastics: See Plastics
Thixotropic: Condition in which material possesses resistance to flow until it is agitated (mixed, pumped, or sprayed).
Tool: A mold.
Tooling Gel Coat Resin: Special, high-performance polyesters designed for mold-making.
Toughness: Measure of ability to absorb energy without failure.
Unidirectional: In one direction.
Vacuum Bag Molding: A molding process for minimizing emissions voids and maximizing reinforcement content by drawing vacuum into a flexible film draped over the part.
Veil: Tissue of fibers which drapes and wets easily.
Voids: Laminate defect that occurs during molding process; characterized by lack of resin material.
Viscosity: Fluid’s resistance to flow.
Volatile Organic Compounds (VOC):  Carbon-containing chemical compounds that evaporate readily at ambient or process temperatures.  Environmental, safety and health regulations often limit exposure to these compounds.
Wax: Mold release agent or surfacing agent.
Weave Print: Extreme form of fiber print resembling architecture of woven or stitched glass ply just below or near gel coat surface.
Wet Layup: Application of liquid resin to dry reinforcement in the mold.
Wetout: Process in which reinforcing material can be completely saturated with resin.
Woven Roving Fabric: Heavy fabrics woven from continuous filaments in roving form.