sprayup

Spray-up is a manufacturing method used to produce fiber-reinforced polymer laminates in open molding. In this process, chopped reinforcing fibers are combined with a resin and sprayed onto a mold using a chopper gun. The most common reinforcement is glass fiber, but carbon fiber or aramid fibers may be used for specialized parts. The resins are typically unsaturated polyester or vinyl ester, with epoxy used in some applications. A gel coat may be sprayed on the mold first to provide a smooth surface finish.

Process and equipment: the mold is prepared and gel coat is applied if used; the spray gun mixes fiber and resin and moves across the mold to lay down successive layers. The fibers are chopped and distributed with resin to form a laminate, often with air assist to improve distribution. After reaching the desired thickness, the laminate is cured, sometimes with heat or vacuum bagging to improve consolidation and reduce voids. Post-curing and trimming may follow, and additional surface finishing can be applied.

Applications and suitability: spray-up is commonly used for large, cost-sensitive parts where a strong straight-line production is advantageous. Typical applications include boat hulls and decks, bathroom and kitchen components, automotive panels, and other large FRP parts. It is favored for lower tooling costs and relatively fast deposition on large surfaces.

Advantages and limitations: the method offers low equipment costs and high deposition rates for large parts, and it accommodates complex molds. Limitations include a rough surface finish that often requires secondary finishing, less control over fiber orientation and resin content, potential for voids, and health and environmental concerns due to isocyanates and solvents. It is generally less suitable for high-performance structural parts compared with prepreg or closed-mold processes.