ACETONE: A commonly used wipe solvent. Also known as 2-propanone and Di-methylketone. It is used for cleaning composite surfaces prior to bonding and also metal surfaces prior to other treatments. It can be used to remove uncured epoxy resin from tools and other items. It is classed as “Seriously Flammable”.

ADDITIVE: Any substance added to another substance, usually to improve properties, such as plasticizers, initiators, light stabilizers, and flame retardants. See also filler.

ADHESIVE: A substance capable of holding two materials together by surface attachment. Adhesive can be in film, liquid, or paste form. In this context, the term is used to denote structural adhesives, i.e., those which create attachments capable of transmitting significant structural loads.

ALLIGATORING: A cosmetic defect in the gel coat layer. It looks like a wrinkled surface which resembles alligator skin. This is often caused by the gel coat being applied too thin.  It can also be caused by not allowing the gel coat to cure long enough before adding subsequent layers.

ARAMID: A type of highly oriented organic material derived from polyamide (nylon) but incorporating aromatic ring structure. Kevlar and Nomex are common name brands for aramid.  It is known for its impact and abrasion resistance. It is used in bullet-proof vests, motorcycle racing cloth and gloves.

BAGGING: Applying an impermeable layer of film over an uncured part and sealing edges so that a vacuum can be drawn. Vacuum Bagging

BIAS FABRIC: Warp and fill fibers at an angle to the length of the fabric. Knitted Fabric

BLISTER: Blister-  A de-bond of paint or other coating from part surface. It is an undesirable rounded elevation of the surface of a plastic with boundaries that are more or less sharply defined, resembling in shape to a blister on the human skin. The blister may burst and become flattened.

BREATHER (BREATHER CLOTH): A loosely woven material such as glass fabric that will serve as a continuous vacuum path over a part or the repair area, but is not in direct contact with the part or the repair area. Vacuum Bagging

CARBON FIBER: Also known as graphite. It is known for its’ strength, being light weight and for its’ good looks.  It is commonly used in the automobile, sporting goods and aerospace industry.  A yard of carbon fiber cloth has millions of microscopic filaments all bundled together.   For instance, in a 3k fiber fabric, each tow (or bundle) of fiber has 3000 filaments in it.  The bundles are woven together to form a fabric. This is what makes it so strong.  Each filament carries part of the load.

CAST: To form material into a certain shape by pouring it into a mold and letting it harden without applying external pressure.

CASTING RESIN: A resin in liquid form that can be poured or otherwise introduced into a mold and shaped without pressure into solid articles.

Catalyst/Curing Agent/Hardener-The word catalyst is most often used when talking about MEKP (methyl ethyl ketone peroxide).  MEKP is added to polyester and vinyl ester resin. It is what causes the chemical reaction that changes the liquid resin to a solid. Curing agent or hardener are words usually used when talking about epoxy resin. As discussed above, epoxies come in two parts, Part A and Part B. Part B is the curing agent or hardener. When mixed together properly, the two parts will cure to a hard finished product.

CHOPPED STRAND MAT (Fiberglass Mat): A mat formed of strands cut to a short length, randomly distributed, without intentional orientation, and held together by a resin binder. The binder is dissolved when resin is applied.  Chopped strand mat is not compatible with epoxy resin.

CHROME FINISH (VOLAN ‘A’): Applied to glass fibers to give good bonding to polyester and epoxy resins.

COMPOSITE MATERIAL: A combination of fiberglass and resin. Fiberglass fabric (including chopped strand mat, carbon fiber, aramid, and roving) is just a limp piece of material until a liquid resin is added.  On the flip side, by itself, resin is just a thick gooey liquid. Polyester, vinyl ester and epoxy are the most commonly used resins in a composite.  Once the resin is mixed with a catalyst, it is added to the fabric.  Enough resin is added to saturate the fabric.  If a mold is used, the fabric and resin will conform to its shape. Over the next few hours, the limp cloth and gooey resin will cure and become a solid material that is much stronger than the individual components were before combined. Resin and fiberglass fabric are not to be used individually but instead together.

COMPOUND: The intimate admixture of a polymer with other ingredients, such as fillers, softeners, plasticizers, reinforcement, catalysts, pigments, or dyes. A thermoset compound usually contains all the ingredients necessary for the finished product, while a thermoplastic compound may require subsequent addition of pigments, blowing agents, etc.

CORE: (A) The central member, usually foam or honeycomb, of a sandwich construction to which the faces of the sandwich are attached or bonded. (B) The central member of a plywood assembly. (C) A channel in a mold for circulation of heat transfer media (D) Part of a complex mold that forms undercut parts. (E) A device on which prepreg is wound.

CORROSION: The deterioration of a metal by chemical or electrochemical reaction resulting from exposure to weathering, moisture, chemicals, or other agents or media.

CURING AGENT: A catalytic or reactive agent that, when added to a resin, causes polymerization. Also called hardener.

DELAMINATION: Separation of the layers of material in a laminate, either local or covering a wide area.  This can occur in the cure or subsequent life.

E-GLASS: A family of glasses with a calcium aluminoborosilicate composition and a maximum alkali content of 2.0%. A general purpose fiber that is most often used in reinforced plastics and is suitable for electrical laminates because of its high resistivity.

EPOXY RESIN: A polymerizable thermoset polymer containing one or more epoxide groups and curable by reaction with amines, alcohols, phenols, carboxylic acids, acid anhydrides, and mercaptans. An important matrix resin in composites and structural adhesives.

FIBER CONTENT: The amount of fiber present in a composite. This is usually expressed as a percentage volume fraction or weight fraction of the composite.

FIBER COUNT: The number of fibers per unit width of ply present in a specified section of a composite.

FIBERGLASS REINFORCEMENT: The fabric material used to reinforce a resin matrix. This includes woven fiberglass cloth, chopped strand mat, carbon fiber, aramid, woven roving, knitted fabric and unidirectional. The fiberglass chosen determines most of the strength of the finished part.

FIBER-REINFORCED PLASTIC (FRP): A general term for a composite that consists of a resin reinforced with cloth, tape, mat, or strands of any fiber form and using any type fiber.

FILL: Yarn oriented at right angles to the warp in a woven fabric. Also called “weft” or “woof”.

FILLER: A relatively inert substance added to a material to alter its physical, mechanical, thermal, electrical, and other properties, or to lower coast or density.

FRP– Fiber reinforced plastic also known as GFRP (Glass Fiber Reinforced Plastic). It is a general term for a resin/fiber composite.

GEL COAT: A quick setting resin, most often a polyester resin, that is applied to the surface of a mold and gelled before lay-up. The gel coat becomes an integral part of the finished laminate, and is usually used to improve surface appearance and bonding. Gel coats come in many colors and will leave a smooth shiny, surface to the finished part. It also adds a layer of protection to the laminate or mold.

HAND LAY-UP: The process of placing (and working) successive plies of reinforcing material or resin-impregnated reinforcement in position on a mold by hand.

HARDENER: A substance or mixture added to a plastic composition to promote or control the curing action by taking part in it. The term is also used to designate a substance added to control the degree of hardness of the cured film.

IMPREGNATE: In reinforced plastics, to saturate the reinforcement with a resin.

KNITTED FABRICS: Fabrics produced by inter-looping chains of yarn.

LAMINATE (noun): A product made by bonding together two or more layers (plies) of material.  When talking about fiberglassing in particular it is the bonding of several layers of fiberglass and resin together.

LAY-UP: The process of placing the reinforcing material in position in the mold.

MEKP: Methyl ethyl ketone peroxide, a catalyst for polyester resins. Highly corrosive.

MICROSPHERES– 3M’s brand name for this is 3M glass bubbles.  They are small, hollow glass spheres used as fillers in epoxy and polyester compounds to reduce density. This filler is lightweight and easy to sand.  It can be used on minor surface repairs.  It makes a good putty for cracks and holes when mixed with resins.

MILLED FIBER: Continuous glass strands hammer milled into very short glass fibers. They come in a variety of lengths such as 1/32″, 1/8″ and 1/4″.   Milled fibers are glass filaments coated with a specific sizing to enhance resin compatibility and milled to a specified bulk density. Useful as inexpensive filler or anti-crazing reinforcing fillers for adhesives.

MOLD: The cavity or matrix into or on which the plastic composition is placed and from which it takes form. To shape plastic parts of finished articles by heat and pressure. The assembly of all the parts that function collectively in the molding process.

MOLDING: The forming of a polymer or composite into a solid mass of prescribed shape and size by the application of pressure and heat for given times. Sometimes used to denote the finished part.

MOLD-RELEASE AGENT: Also known as a release agent or parting film, depending which kind is being used. The two most commonly used mold releases are a carnauba based wax and PVA (film).  Mold release is used to allow parts to be easily removed from the original plug or the mold. Plus it adds a durable surface finish to the part and keeps both the part and the mold from being damaged during production.  A mold release is essential when breaking in a new mold.  It ensures your part will separate from the mold cleanly rather than sticking to it.

MOLD SURFACE: The side of a laminate that faced the mold (tool) during cure, often called the tooled surface.

ORANGE PEEL: A pebbly texture on the cured gel coat similar to an orange peel. It is caused by PVA (mold release film) if the gel coat is sprayed onto a mold.  It can also be caused by spraying gel coat onto the outside of the part.  Gel coat is thicker than paint and does not lay down as smooth.  This texture on the finished product will need to be polished for a better cosmetic look

PEEL PLY: A layer of open-weave material, usually fiberglass, polyester, or heat-set nylon, applied directly to the surface of a prepreg lay-up. The peel ply is removed from the cured laminate immediately before bonding operations, leaving a clean resin-rich surface that may need no further preparation for bonding, other than application of a primer where one is required. Vacuum Bagging

PLAIN WEAVE: A weaving pattern in which the warp and fill fibers alternate, that is, the repeat pattern is warp/fill/warp/fill, etc. Both faces of a plain weave are identical.

POLYMER: A large molecule created by a large number of smaller molecules, called monomers, in a regular pattern.

POT LIFE ALSO KNOWN AS WORKING LIFE– The length of time, at some specified temperature, that a catalyzed resin is workable.  A small amount of control can be had when working with resin.  More or less (no less than 1% and no more than 2%) MEKP can be added to polyester and vinyl ester resins depending on the amount of time needed to work.  Epoxy resin comes in two parts, Part A and Part B. Part B is what hardens the epoxy resin. It comes in fast, medium and slow speeds. The temperature of the working area also determines pot life.

PRIMER: A coating applied to a surface, before the application of an adhesive, lacquer, enamel, etc., to improve the adhesion performance or load carrying ability of the bond. Some primers contain a corrosion inhibitor.

REINFORCEMENT: A strong material bonded into a matrix to improve its mechanical properties. Reinforcements are usually long fibers, chopped fibers, etc. A material used to reinforce, strengthen or give dimensional stability to a part.

RELEASE AGENT: A material that is applied in a thin film to the surface of a mold to keep the resin from bonding to the mold. Also called parting agent or mold release

RELEASE FILM: An impermeable layer of film that does not bond to the resin being cured. Mold Release

RESIN: In reinforced plastics, the material used to bind together the reinforcement material (fiberglass cloth). The matrix. Most resins are polymers. The most common resins in the fiberglass industry are polyester, vinyl ester and epoxy. Resin holds the reinforcement together and helps it conform to the wanted shape.  Resin fills the fiberglass weave when laminating.

RESIN TRANSFER MOLDING (RTM): A process whereby catalyzed thermosetting rein is transferred or injected into an enclosed mold in which the fiber reinforcement has been placed. Cure is normally accomplished without external heat. RTM combines relatively low tooling and equipment costs with the ability to mold large structural parts. In general, thermoplastics are too viscous to be used in RTM even if heat is applied.

ROOM-TEMPERATURE VULCANIZING (RTV): Vulcanization or curing at room temperature by chemical reaction; usually applies to silicones and other rubbers.

ROVING: A number of yarns, strands, tows, or ends collected into a parallel bundle with little or no twist. This term is applied most commonly to glass and Kevlar.

SANDWICH CONSTRUCTIONS: Panels composed of a lightweight core material, such as honeycomb, foamed plastic, etc., to which two relatively thin, dense, high-strength or high-stiffness faces or skins are adhered.

SATIN WEAVE: Weaving pattern producing a satin appearance. “Eight-harness” means the warp yarn crosses over seven fill yarns and under the eighth (repeatedly). Also produced as four harness and five harness.

SELVAGE: The woven-edge portion of a fabric parallel to the warp, finished off so as to prevent the yarns from unraveling. Fiberglass tape typically has a selvage edge. It gives it a nice clean look.

SOLVENT: A substance (usually a liquid) used as a dissolvent or cleaning material during reinforced plastics operations. It is also often flammable or toxic. It should be handled in accordance with safety instructions.

STRUCTURAL ADHESIVE: Adhesives used for transferring required loads between adherents exposed to service environments typical for the structure involved.

SUBSTRATE: A material upon the surface of which as adhesive or resin is spread for any purpose such as bonding or coating.

TACK-FREE: A condition in which a plastic material can be dented with an inert object without sticking to it. It is indicative of a definite stage of hardening. A laminating resin will cure with a tack (stick) unless a surfacing agent or finishing resin is used. A finishing resin has wax that will rise to the top when cured.  This will create a nice hard finish.

THERMOSET PLASTIC RESIN– A plastic that goes from liquid to solid following a chemical reaction. The solid cannot be melted back into a liquid.

THIXOTROPIC: Concerning materials that are gel-like at rest, but fluid when agitated. Having high static shear strength at the same time. To lose viscosity under stress.

THREAD COUNT: The number of yarns (threads) per inch or centimeter in either the lengthwise (warp) or crosswise (fill or weft) direction of woven fabrics.

TOOLING– The molds and fixtures used to produce a composite article (fibers and resin). Tooling may be made with any suitable material but composites are a popular choice.

TWO-COMPONENT ADHESIVE: An adhesive supplied in two parts that are mixed before application. Such adhesives usually cure at room temperature.

UNIDIRECTIONAL– Most of the fibers are oriented in the same direction. This makes the majority of the strength in one direction.

VACUUM BAG MOLDING: A process in which a sheet of flexible transparent material plus bleeder cloth and release film are placed under the layup on the mold and sealed at the edges. A vacuum is applied between the sheet and the lay-up. The entrapped air is mechanically worked out of the lay-up and removed by the vacuum, and the part is cured with temperature, pressure, and time.

VINYL ESTERS: A class of thermosetting resins containing esters of acrylic and/or methacrylic acids, many of which have been made from epoxy resin. Cure is accomplished as with unsaturated polyesters by copolymerization with other vinyl monomers, such as styrene.

VULCANIZATION: A chemical reaction in which a rubber is cured by reaction with sulfur or other suitable agents.

WARP: The yarn running lengthwise in a woven fabric. A group of yarns in long lengths and approximately parallel. Fabrics are tensional in the warp direction during weaving. The weft is not tensioned.

WEATHERING: Exposure of plastics to the outdoor environment.

WEAVE: The particular manner in which a fabric is formed by interlacing yarns. Usually assigned a style number.

WEFT: The transverse threads or fibers in a woven fabric. Those fibers running perpendicular to the warp. Also called fill, filling yarn or woof.

WET LAY-UP: A method of making or repairing a reinforced product by applying the resin system as a liquid when the reinforcement is put in place.

WET-OUT: The process of saturating the fiberglass fabric with epoxy or polyester resin to the point that all strands and holes are filled.

WORKING LIFE: The period of time during which a liquid resin or adhesive, after mixing with catalyst, solvent, or other compounding ingredients, remains usable. Also called pot life.

WOVEN ROVING: A heavy glass fiber fabric made by weaving roving or yarn bundles.