Gelcoat

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Gelcoat

A gelcoat is a material used to provide a high quality finish on the visible surface of a fibre-reinforced composite material

Composite material

Composite materials are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure....
. The most common gelcoats are based on epoxy

Epoxy

In chemistry, epoxy or polyepoxide is a thermosetting epoxide polymer that cures when mixed with a catalyst agent or hardener. Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A....
or unsaturated polyester

Polyester

Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate ....
resin

Resin

Resin is a hydrocarbon secretion of many plants, particularly Pinophyta. It is valued for its chemical constituents and uses, such as varnishes and adhesives, as an important source of raw materials for organic synthesis, or for incense and perfume....
chemistry. Gelcoats are modified resins which are applied to moulds in the liquid state. They are cured to form crosslinked polymer

Polymer

A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties....
s and are subsequently backed up with composite polymer matrices, often mixtures of polyester resin and fiberglass

Fiberglass

Fiberglass, , is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer or glass-reinforced plastic , is called "fiberglass" in popular usage....
or epoxy resin with glass, kevlar

Kevlar

Kevlar is the registered trademark for a light, strong aramid synthetic fiber, related to other aramids such as Nomex and Technora.Developed at DuPont in 1965 by Stephanie Kwolek it was first commercially used in the early 1970s as a replacement for steel in racing tires....
and/or carbon fibres.

The manufactured component, when sufficiently cured and removed from the mould, presents the gelcoated surface.

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Encyclopedia

A gelcoat is a material used to provide a high quality finish on the visible surface of a fibre-reinforced composite material

Composite material

Epoxy

Polyester

Resin

Polymer

Fiberglass

Kevlar

Pigment

A pigment is a material that changes the color of light it Reflection as the result of selective color absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which the material itself emits light....
ed to provide a coloured, glossy surface which improves the aesthetic appearance of the article, such as a counter made with cultured marble

Cultured marble

Cultured marble, also referred to as cast polymer, is a plastic composite blend of high strength polyester resin and marble dust formed in a variety of molds to make a single piece article such as bathtubs, shower pans and vanity tops with a surface that resembles marble....
.

Many marine craft are manufactured using composite materials. The outer layer is often a gelcoat, typically 0.5mm - 0.8mm in thickness. Gelcoats are designed to be durable, providing resistance to ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 400 nanometer to 10 nm, and energies from 3 Electron volt to 124 eV....
degradation and hydrolysis

Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
. The gelcoat will often carry a pigment that provides the finish colour to the moulded item. Specialised gelcoats can be used to manufacture the moulds which in turn are used to manufacture components. These require very high levels of durability to overcome the mechanical and thermal stresses

Stress (physics)

In continuum mechanics, stress is a measure of the average amount of force exerted per unit area. It is a measure of the intensity of the total internal forces acting within a body across imaginary internal surfaces, as a reaction to external applied forces and body forces....
encountered during the curing and demoulding processes.

Suitable resin chemistries for the manufacture of gelcoats vary, but the most commonly encountered are unsaturated

Saturation (chemistry)

In chemistry, saturation has five different meanings:#In physical chemistry, saturation is the point at which a solution of a substance can dissolve no more of that substance and additional amounts of it will appear as a Precipitation ....
polyesters or epoxies. Within each of these categories, the resin chemistries are further subdivided.

In addition to any pigment a gelcoat will, if necessary, contain a thixotropic

Thixotropy

Thixotropy is the property of some Non-Newtonian fluid Power-law fluid fluids to show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower is its viscosity....
additive to assist its tenacity to vertical portions of the mould whilst it cures.