Small sunken dots in the gelcoat surface, generally caused by a foreign particle in the liminant.

What does it mean to cure?

The polymerization or the transforming from the liquid to the solid state after the catalyst has been added.

What is Barcol hardness?

A determination of hardness of a polyester using a Barcol Impressor.

What is Benzoyl Peroxide?

(BPO) The catalyst used in conjunction with aniline accelerators or where heat is used as an accelerator.

What is a binder?

Bonding resin applied to glass fibers to hold fibers in position in a mat structure.

What is a composite?

Dissimilar materials laminated together to form a single structure, for example, resin, gelcoat, glass.

What is a core?

1. The central member of a sandwich construction.
2. A channel in a mold for circulation of heat-transfer media.
3. Part of a complex mold that molds undercut parts, also called core pin.

What is a diluent?

Diluting agent that causes reducing or thinning.

What is acetone?

In an FRP context, acetone is primarily useful as a cleaning solvent for removal of uncured resin from applicator equipment and clothing. Very flammable liquid.

What is additive?

Substance added to resin mix to impart special performance qualities, such as ultraviolet absorbers, flame retarding materials (antimony trioxide, chlorinated waxes).

What is air-drying?

To cure at room temperature with the addition of catalyst but without the assistance of heat and pressure.

What is alligatoring?

Wrinkling of the gelcoat film that resembles alligator hide.

What is an accelerator?

An additive that reduces the gel and curing time of thermosetting plastics such as polyester gelcoat and resin. Also called promoter or activator.

What is bag molding?

A technique for forming and pressure-hardening plastics or plastics laminates by means of air pressure, vacuum and/or heat in a flexible or semi-flexible bag or autoclave, usually in connection with a rigid dye or mold.

What is bi-directional?

An arrangement of the reinforcing fiber strands in which half the strands are laid at right angles to the other half, a directional pattern that gives the maximum product strength to those two directions.

What is catalyst injection?

Used with spray equipment to catalyze the polyester at the spray gun, therefore eliminating the need to clean the system within the gel time of the polyester. Internal mix guns do require a solvent flush for cleaning the gun head.

What is catalyst?

(Peroxide) In FRP terms, a substance add to the resin or gelcoat in controlled quantites to make it cure more rapidly. Usually it oxidizes an accelerator, creating free radicals, which in turn cures the resin or gelcoat.

What is chalking?

Dry, powder-like appearance or deposit on gelcoat surface.

What is chopped strand?

Continuous strand yarn or roving cut up into uniform length, usually from 1/32"to 2"long. Lengths up to 1/8" are called milled fibers

What is cloth?

A fine weave or woven fiberglass.

What is contact molding?

An open-mold process that includes spraying, followed by hand lay-up or spray-up with glass and resin. Also called contact laminating or low pressure laminating.

What is crazing?

Cracking of the resin due to internal stress.

What is cross-laminated?

A type of laminating where some of the layers are oriented at right angles to the remaining layers with respect to the grain or the strongest direction in tension.

What is delamination?

The separation of a laminant into layers owing to failure of adhesion of the binder or failure of cohesion of the filler.

What is density?

Weight per unit of volume, usually expressed as pounds per cubic foot.

What is dimensional stability?

Capability of an item to maintain its constructed dimensions without distorting.

What is dispersion?

The means of incorporating pigments into a polyester.

What is distortion?

A wavy gelcoat image often found in conjunction with print through. Commonly caused by a problem in the laminating system.

What is draft?

An engineering function taken into consideration when building molds to facilitate easier removal of parts from the mold. A minimum of three degrees is recommended.

What is drain out?

The leaking, sagging, and puddling of the laminating resin from the laminate.

What is e-glass?

Electrical grade glass.

What is encapsulating?

Describes enclosing an article in a closed envelope of plastics by immersion. Milled fibers or short chopped strands are often poured with the catalyzed resin into open molds for casting electrical components.

What is exothermic heat?

Internally developed heat accompanying a chemical reaction.

What is fading?

Loss of color in the gelcoat.

What is fiber?

An individual rod of glass of sufficiently small diameter to be flexible, having a known or approximate limit of length.

What is fiberglass?

Fibers similar to wool or cotton fibers but made from glass; sometimes called fibrous glass. Glass fiber forms include cloth, yarn, mat, milled fibers, chopped strands, roving, woven roving.

What is filament winding?

A process for production of high-strength, lightweight products in which tape, roving or single strands are fed from a creel through a bath or resin (or fed dry using impregnated roving) and wound on a suitably designed mandrel. The wound mandrel can be cured at room temperature or in an oven.

What is filament?

A single thread-like fiber or a number of these fibers put together. A variety of fiber characterized by extreme length, which permits its use in yarn with little or no twist and usually without the spinning operation required for fibers.

What is fillers?

Relatively inert organic or inorganic materials which are added to plastics resins or gelcoats for special flow characteristics, to extend volume, and lower the cost of the article being produced.

What is finish?

As surface treatment give to the fibers or filaments after they are fabricated into strands, yarn, or woven fabrics to allow the resins to flow freely around and adhere to them.

What is fish eye?

A circular separation in a gelcoat film generally caused by contamination such as silicone, oil, dust, and water.

What is flash point?

The lowest temperature at which a substance gives off enough vapors to form a flammable or ignitable mixture with air near the surface of the supstance being tested.

What is frp?

Fiberglass Reinforced Plastics.

What is fumed silica?

(Aerosil, Cabosil) A very low-weight thickening agent used in polyesters to increase thixotropic qualities.

What is gel time?

The length of time that a catalyzed polyester remains workable-starts to solidify.

What is gel?

A partial cure stage of plastics resins in a viscos, jelly-like state where the liquid material starts to transform into a solid.

What is gelcoat?

A surface coat, either colored or clear, providing a cosmetic enhancement and exposure improvements to a fiberglasslaminate.

What is hand layup?

Laminating by "hand" as opposed to using spray equipment. Usually requires glass mats and fabrics in sheet form.

What is honeycomb?

A manufactured product of sheet metal or resin-impregnated sheet material (paper, fibrous glass, etc.)that has been formed into hexagonal shaped cells. Used as core material for sadwich construction.

What is hot pot?

Catalyst is mixed with the gelcoat or resin in the material container prior to spraying, as opposed to internal or external gun mixing.

What is humidity?

Moisure content of the air.

What is hydrophobic?

Moisture absorbing capability.

What is impregnate?

The saturation of fiberglass with a resin.

What is inhibitor?

A substance designed to slow down or prevent a chemical reaction.

What is iso?

Abbreviated terminology for isophthalic acid type resins and gelcoats.

What is laminant?

The product.

What is laminate?

The process.

What is laminated plastics?

Material consisting of super-imposed layers of synthetic resin-impregnated or coated filler that has been bonded together usually by means of heat and pressure, to form a single piece.

What is lamination?

the laying on of layers of reinforcing materials and resin, much like the build-up of plywood. Several layers of material bonded together.

What is lay-up?

Placing reinforcing material onto the mold and applying resin to it; can be done by hand or by using spray-up equipment. Lay-up is sometimes used as a term for the workpiece itself.

What is mass?

The quantity of matter contained in a specific body. In reference to polyesters, mass is measured in mils or inches thickness of a film or casting.

What is master?

(Plug) The permanent tool used to build molds for the manufacture of fiberglass parts.

What is mat?

A randomly distributed felt of glass fibers held together with a binder, used in reinforced plastics lay-up molding.

What is mek peroxide?

(MEKP) Abbreviation for methyl ethyl ketone peroxide used to catalize polyester and vinylester resin based products.

What is mek solvent?

Abbreviation for methyl ethyl ketone; a colorless, flammable liquid commonly used in gun clean-up procedures.

What is mil?

The unit used in measuring film thickness and the diameter of glass fiber strands, wire, etc. (one mil = .001").

What is milled fibers?

Crushed glass used generally for making glass filled putty.

What is moisture absorption?

The pick-up of water vapor form air by a material. It relates only to vapor withdrawn from the air by a material and must be distingished from water absorption, which is the gain in weight due to the take-up of water by immersion.

What is mold release?

A substance used to coat the mold in order to prevent sticking and for ease of part release.

What is mold?

1.To shape plastic parts by heat and pressure. 2.The cavity or matrix into/onto which the plastics composition is placed and from which it takes its form. Female: made into; Male: made onto. 3.The assembly of all parts that function collectively in the molding process.

What is molding?

The forming of glass materials and resin by various means, such as contact, pressure, matched die, and continuous laminating, into a given shape over a mold, and holding that shape by the mold until the resin cures.

What is monofilament?

A single filament of indefinite length. Monofilaments are generally produced by extrusion.

What is non-air-inhibited resin?

A resin in which the surface cure will not be inhibited or stopped by the presence of air. A surfacing agent has been added to exclude air from the surface of the resin.

What is non-volatile material?

Portion remaining as solid under specific conditions short of decomposition.

What is orange peel?

Backside of the gelcoated surface that takes on the rough wavy texture of an orange peel.

What is ortho?

Abbreviation for orthophthalic acid type resins and gelcoats.

What is parting agent?

See mold release.

What is pattern?

The initial model for making fiberglass molds.

What is pigment?

The ingredient used in gelcoats to impart color.

What is pinholes?

Small air bubbles in the gelcoat film, few enough to count. Generally larger size than porosity.

What is plastics?

Usually synthetic materials chemically created from organic substances classified as thermoplastics or thermosets.

What is plug?

See master.

What is polyester?

(Unsaturated)A resin formed by the reaction between dibasic acids and dihydroxy alcohols, one of which must be unsaturated (typically maleic anhydride)to permit cross-linking.

What is polymer?

A large chemical chain composed of many identical groups, such as polystyrene.

What is polymerization?

The chemical reaction of crosslinking the molecules in the resin. See also cure.

What is polyvinyl alcohol?

(PVA)A liquid water soluble release agent for polyester.

What is porosity?

Small air bubbles in the gelcoat film; too numerous to count. Generally smaller in size than pinholes.

What is post-cure?

Exposure to the cured resin to higher temperatues than during curing, necessary in certain resins to attain complete cure and ultimate mechanic properties.

What is pot life?

See gel time.

What is potting?

Similar to encapsulating, except that steps are taken to insure complete penetration of all the voids in the object before the resin polymerizes.

What is pre-release?

Premature release of the gelcoat or laminant from the mold.

What is preform?

A preshaped fibrous reinforcement formed by distributionof chopped fibers by air, water flotation, or vacuum over the surface of a perforated screen to the approximate contour and thickness desired in the finishced part. Also a compact pill of compressed premixed materials.

What is premix?

Reinforcing material mixed with resin, and usually with pigment, filler and catalyst, before placing in the mold. Premix can be extruded into ropes or used in bulk form.

What is prepeg?

Reinforcing material impregnated with thickened resin.

What is pressure bag?

A tailored bag (usually rubber sheeting)which is placed against the lay-up in an open mold, hand lay-up process. Air or steam presure (up to 50 psi)is applied between the bag and a pressure plate located over the mold.

What is primary laminate?

Laminate applied after the skin coat has cured. Generally thicker than the skin coat.

What is print through?

"Telegraphing" of the image of glass strands through the gelcoat.

What is radius?

Of a roller; describes the curve of the roller in relation to the size of the brushstroke.

What is reinforcement?

A strong inert material bound into plastics to improve its strength, stiffness, and impact resistance. Usually long fibers of glass, sisal, cotton, etc., in a woven or nonwoven form.

What is release agent?

See mold release.

What is resin?

Any of a class of solid semisolid organic products of natural or synthetic origin, generally of high molecular weight having no definite melting point. Used in reinforced products to surround and hold fibers. Most resins are polymers.

What is roving?

(Filament Winding)A collection of bundles of continuous filaments either as untwisted strands or as twisted yarns. For filament winding they are generally wound as bands or tapes with as little twist as possible.

What is sandwich lay-up?

A lamination composed of two outside layers of rinforced material such as glass mat and an inside layer or layers of honeycomb, glass cloth, or other light-weight core material.

What is shelf life?

The length of time an uncatalyzed polyester remains workable while stored in a tightly sealed container.

What is skin coat?

The first layer of laminate next to the gelcoat. Generally only 1/16" thick to afford good rollout and to reduce heat.

What is specific gravity?

The ratio of the weight of any volume of a substance to the weight of an equal volume of some substance taken as a standard unit; usually water for solids and liquids, and air or hydrogen for gases.

What is spray-up?

A process in which glass fibers, catalyzed resin and catalyst are simultaneously deposited in a mold. Roving is fed through a chopper and ejected into a resin stream directed at the mold. Resin catalyst and accelerator may be sprayed form one or two guns. The glass resin mix is then rolled by hand before curing.

What is styrene monomer?

An unsaturated hydrocarbon, used in plastics. In polyester, it is a co-reactant diluent.

What is surfacing agent?

A material that allows the surface of polyester to cure. It limits adhesion of another coat of resin if the first is thoroughly cured. It may be removed by sanding or rubbing with steel wool.

What is tack?

Stickiness.

What is thixotropic?

A term describing materials more jelly-like at rest than when stirred or agitated. Agitation (shear)reduces the gel and increased the folw characteristics.

What is undercut?

Negative or reverse draft on the mold. Split molds are necessary to shape pieces that are undercut.

What is vacuum bag molding?

Process for eliminating voids and forcing out entrapped air and excess resin from lay-ups by drawing a vacuum into a cellophane or polyvinyl acetate bag draped over the part.

What is vapor barrier?

A material through which water vapor will not pass readily or at all.

What is viscosity?

The internal resistance of a fluid to flow; thickness.

What is wax?

A mold release agent.

What is wetout rate?

The speed with which a reinforcing material can be completely saturated with resin. This rate is usually determined visually and measured in elapsed time.

What is woven roving fabric?

Heavy fabrics woven from continuous filament in roving form. They drape well, are quickly impregnated and intermediate in price between mats and yarn cloths.

What is woven tape?

Tape of various thicknesses woven from continuous filament yarns.