Gelcoat

Gelcoat is a resin-based coating applied to molds used to manufacture fiber-reinforced plastics (FRP) composites. It is typically the first material introduced into the mold and, upon curing, forms the outer surface of the finished part. This surface is visible and exposed to the environment, providing the finished product with its desired color, texture, and protection against degradation.

The primary purpose of gelcoat is to provide an aesthetic and protective layer for the composite part. It offers resistance to UV degradation, weathering, abrasion, and water intrusion. Gelcoats can be pigmented to achieve a wide range of colors and can be formulated to offer specific properties, such as chemical resistance or fire retardancy.

Gelcoats are typically thermosetting polymers, most commonly unsaturated polyester or vinyl ester resins. They are applied as a liquid and then cured, either through the addition of a catalyst (chemical cure) or by exposure to ultraviolet (UV) light (UV cure). The curing process transforms the liquid resin into a solid, durable layer.

There are several types of gelcoats, each formulated for specific applications and performance requirements. Common types include:

• General Purpose Gelcoat: A standard gelcoat offering good all-around performance.

• Orthophthalic Gelcoat: Cost-effective gelcoat suitable for general applications where high performance is not critical.

• Isophthalic Gelcoat: Offers improved water resistance and durability compared to orthophthalic gelcoats.

• Vinyl Ester Gelcoat: Provides superior chemical resistance, blister resistance, and higher temperature resistance, making it ideal for demanding applications.

• Tooling Gelcoat: Formulated to withstand repeated use and the stresses of molding processes, used for creating durable molds.

Proper application of gelcoat is critical to achieving a high-quality finish. Factors influencing the final result include the preparation of the mold surface, the application technique (spraying is common), the curing process, and the environmental conditions during application. Imperfect application can lead to issues like air entrapment, orange peel texture, cracking, or delamination.