ACCELERATOR
Material used in conjunction with a catalyst to produce and hasten the internal heat reaction in the liquid resin for cure.

ACETONE
A highly flammable and toxic cleaning fluid used to remove uncured resin from tools and clothing. Acetone is a solvent which will ruin some synthetic plastic such as rayon and Dacron.

ACTIVATOR
See Accelerator

AIR BUBBLES
Entrapment of air particles in resin or a fiberglass laminate caused by improper mixing of the resin, improper wetting out of a laminate, forming of the fiberglass material around abrupt corners, etc. Air bubbles weaken the bond in a fiberglass laminate.

AIR-INHIBITED RESIN
A resin which will not completely cure or "set up" in the presence of air. Polyester resin which does not contain wax is classed as "air in-hibited".

BINDER
A bonding agent used to adhere the various fibers together in the manufacturing of fiberglass materials, especially mats.

BOND
The adhesion between two materials. Also, to attach materials together by means of adhesive agent.

BUTT JOINT
A joint made by positioning materials together end-to-end or side-to-side without an overlap.

CATALYST
Material added to resin to make it cure rapidly by oxidation with an accelerator as in polyester resins. This causes the heat which in turn cures the resin.

CAVITY MOLD
The female half of a mold.

CHOPPER GUN
A special spray gun used for spray-up laminating which chops predetermined lengths of fiberglass roving or strands, and deposits them together with catalyzed resin at the same time onto the mold surface.

CLOTH
A woven fabric made from fine yarns of fiberglass.

COLOR PIGMENTS
Coloring material added to resins to give them color, much the same as pigments used in paints.

COMPOSITE
Type of construction using two or more different materials, such as resin and fiberglass material together.

CRAZING
Hairline cracks either within or on the surface of fiberglass laminates, caused by stresses generated by excessive heat during cure, removal from the mold, impact, or flexing.

CURE
The changing of the liquid resin to a solid state. Once the resin begins to cure, the process can not be reversed, the technical term for cure is " polymerization ".

CURE TIME
The time required for the liquid resin to reach a point when it is hard enough to have other processes performed with it, such as sanding or finishing, or when it is no longer "tacky" or "sticky". Technically, it is the time required for the resin to reach "polymerized state" after the catalyst has been added.

DELAMINATION
Separation or failure of the bond in laminate layers from each other or from another surface material.

DIMENSIONAL STABILITY
The ability to retain constant shape and size, as opposed to "stretching" and "shrinking".

DRAPEABILITY
The ability of a fiberglass material to conform to contours, corners, and shapes when saturated with resin.

EPOXY RESIN
Thermosetting resins in boat work of a two-part type, that when combined, cure and form into a extremely hard and tough product. They will adhere well to virtually any material, shrink less than polyester resins, have generally greater strength, and absorb less water, although they are much more expensive.

EXOTHERMIC HEAT
The heat given off by the resin developed internally during the curing process, or "polymerization". It is caused by the reaction of the accelerator and the catalyst when mixed in polyester resins, and by the hardener in epoxy resins.

FEATHER EDGE
The process of tapering the edge of a resin-saturated fiberglass material to blend with the adjoining surface, as opposed to having an abrupt edge.

FIBERGLASS
Fiber similar to those of other fabrics, but made from glass.

FILAMENT
A hair-like particle or "rod" of glass used to make fiberglass yarns and threads. A fiberglass filament can be made in virtually an endless length.

FILLER
Material added to resin to extend the volume or change the qualities of the resin. There is a limit to the amount of filler that can be added to the resin without affecting the desirable qualities of the resin.

FILLET
A rounded filling on an inside corner or angle.

FINISH
The surface cleaning treatment applied to the glass fibers after weaving them into cloth in order to allow the resin to flow freely around and adhere to them. The finish determines the quality of the adhesion between the glass and the resin.

FIRE-RETARDANT
Resin type which has been formulated with chemicals to reduce or eliminate its tendency to burn when once cured or "polymerized".

FLEXIBILITY
A qualitative term used to describe the amount of rigidity imparted by a resin after it cures. Resin is usually classed as either flexible, semi-flexible (or semi-rigid), and rigid, but the terms are largely subjective.

GEL/GELATION
The partial cure of polyester resin to a semi-solid or "jelly-like" state.

GEL COAT
A thin surface coat of specially formulated polyester resin used as the surface covering.

GEL TIME
The time it takes to change liquid resin to a non-flowing gel. Also the time available for working the resin once applied.

HAND LAY UP
The application of fiberglass laminates using manual labour usually in a female mold.

INHIBITOR
An additive to polyester resin which retards curing or polymerization thereby extending the shelf life of the resin. It also influences gel time and exothermic heat.

LAMINATE
A material or composition made from successive layers of resin and fiberglass materials bonded together.

LAMINATION
The laying on of layers of fiberglass materials and resin, much like the build-up of plywood laminations. The layers of material are bonded together with resin to form the laminate.

LAP JOINT
A joint made by positioning one material over another end-to-end or side-by-side as opposed to a butt joint. The joint consists of two layers of material.

LAY UP
The placing of fiberglass reinforcing materials onto the mold surface and applying the resin to form the completed laminate.

MAT
Randomly oriented strands of glass fibers formed into a felt and held together with a binder, usually of thinned polyester resin in a powder-like form.

MOLD
An appliance or device used to shape and or duplicate a part.

MOLD RELEASE
See Parting Agent

MONOMER
The technical word for compound which is usually in liquid form and has the ability to be changed into a polymer (solid form), or "polymerized". Styrene is a common monomer used in polyester resins.

NON - AIR - INHIBITED RESIN
A resin which will completely cure or "set-up" in the presence of air. A surfacing agent (usually wax) is added to the resin which floats to the surface to exclude the air from the resin surface, thereby allowing it to cure or "polymerize".

PARTING AGENT
Any material used to coat the mold to prevent the molded part from sticking when being removed, or a material used to keep resin from sticking to any part of the work.

PLUG
A male form identical in shape to the finished object over which a female mold is fabricated.

POLYESTER RESIN
Thermosetting resins which require the addition of a catalyst and accelerator to effect the cure. See also Epoxy Resin.

POLYMER
The technical word for the end product which is usually solid, and produced from a monomer.

POLYMERIZATION
The chemical reaction of monomer, usually from a liquid state to a solid state. See also Cure.

POT LIFE
The length of time that the catalyzed resin remains workable while in a container until it must be discarded. Similar to Gel Time (see also) except that gel time refers to the resin on the surface.

PROMOTER
See Accelerator

RELEASE AGENT
See Parting Agent

RESIN
A liquid plastic substance about the consistency of honey and used in conjunction with fiberglass materials to form a laminate.

RESIN RICH
An area, especially in a laminate, where too much resin has been applied in relation to the fiberglass reinforcing material. The opposite of a DRY SPOT or "resin starved" area. Also referred to as a "resin pocket" and "resin streak".

ROVING
Continuous strands of glass fibers grouped together to form an untwisted yarn or rope. Rovings are commonly used for chopper gun spray-up laminates and to form woven rovings.

SANDWICH CONSTRUCTION
A type of fiberglass construction which resembles a sandwich consisting of relatively dense but high-strength facings bonded to a less dense but thicker intermediate material or "core".

SET UP
Resin which cures and hardens is said to have "set up" or "polymerized".

SHELF LIFE
The length of time a uncatalyzed resin remains usable while stored in a sealed container. Most polyester resins have a useful shelf life of from six months to a year.

SIZING
The surface treatment on glass fibers during the fiber forming operation which aids in machine manufacture as well as allowing the resin to adhere to the fibers in use, as is the case with mats and rovings. Sizing is similar to FINISH for cloth, but because mats and rovings are not "dirtied" by the weaving process, no finish is required.

SPRAY- UP
A method of fiberglass lay up performed with a chopper gun (see also) which cuts and deposits fiberglass rovings and catalyzed resin onto the mold surface. See also Hand Lay Up.

SQUEEGEE
Any tool used to wet out a laminate with a smothing, spreading, or wiping action, in order to prevent wrinkles and remove air bubbles.

STRAND
A bundle of continuous fiberglass filaments.

STYRENE
A water-thin liquid hydrocarbon monmer which is primary ingredient of polyester resin. Also can be used as a thinner of polyester resin.

SURFACING AGENT
Material added to polyester resin or used in association with it to prevent air from reaching the surface of polyester resin so the resin can cure.

SURFACING MAT
A lightweight but rather stiff mat used next to gel coat in a female mold to improve surface appearance of the final product as well as minimize water absorption.

SYNTACTIC FOAM
Resin which has been made lower in. density, lighter in weight, less viscous, and generally stretched out by the addition of fillers.

THERMOPLASTIC RESIN
A type of resin which can be repeatedly softened or reformed by the application of heat, and can be rehardened by cooling.

THERMOSETTING RESIN
A type of resin which will undergo a chemical change from a liquid state as the result of the heat induced by the addition of certain materials. Once it becomes solid, it cannot be reformed by reheating. Polyester and epoxy resins are of the thermosetting type.

THICKENER
Material added to resin to thicken or increase the viscosity of the resin so it will not flow as readily.

THINNER
Material added to resin in order to thin it or lower the viscosity of the resin.There is a limit to the amount of thinner that can be added without affecting the desirable qualities of the resin. Styrene (see also) is the common thinner for polyester resin, although acetone will thin resin also, but should generally not be used for this purpose.

THIXOTROPIC
A quality of some resins to thicken at rest but become fluid again on agitation and stirring. Thixotropic resins are used in boat work to minimize runs and sags on vertical surfaces.

UNDIRECTIONAL ROVING
Heavy crimped parallel rovings with a smaller number of light rovings at right angles to them so that high directional strength properties can result in a laminate.

VISCOSITY
The measure of the resistance of a liquid to flow. A more viscous liquid will not flow as easily as one that has less viscosity.

WET OUT
The ability of a resin to quickly saturate the fiberglass material.

WOVEN ROVING
Fiberglass rovings woven into a coarse fabric much heavier than, but similar to, plain sqaure weave cloth fabric.

YARN
Twisted strand or strands of glass fibers which can be woven, braided, served, and processed on conventional textile equipment.