Gel coats and veils provide the finishing touch.
Composites manufacturers today use surface finishes like gel coats and veils to improve their parts’ appearance and durability. But when their predecessors in the 1950s developed gel coats, they weren’t concerned about appearance. They were searching for a way to minimize the damage that fiberglass products were causing to their tools.
“Companies took the same type of resins that they used to manufacture glass fiber laminates, thickened them up, added filler, painted them on the mold and then made the parts,” says Rick Pauer, market manager at Polynt. “People started liking the look that the gel coat provided, so the next level was to give color or surface enhancements to the FRP parts.”
Boat builders saw the potential of gel coat and began asking manufacturers to incorporate other properties into it like ultraviolet (UV) and blister protection and water resistance. The marine industry is still the largest customer for gel coats, but manufacturers of transportation products (RVs, trucks and buses) and sanitary products (tub and shower surrounds) are also big purchasers.
For all of these markets, “the performance of a gel coat is very much about aesthetics; there is the element of surface protection, but a significant amount of it is appearance,” says Harry Certain, business manager, Interplastic Corp. “People are saying ‘I want my RV to look great 15 years from now; I want my boat to look brand new after a number of years.’”
Gel coats provide one big advantage over thinner coatings like paint. “Having a uniform color for 20 mils allows easy repairs to be made in a gel-coated surface,” says Pauer. “The agriculture, transportation and marine markets greatly appreciate the reparability of gel-coated composites where scratches and graffiti can be easily buffed back to their original surfaces. In the architectural market, the thicker gel coat is often sand blasted to provide a textured surface that looks much like concrete or terra-cotta stone.”
A Balancing Act
Developing cost-effective, quality gel coats is not an easy task. Scott Crump, director of research and development – gel coats/colorants at Interplastic, says that a typical gel coat formula contains between 15 and 25 different components. A change to one ingredient to improve a particular property can adversely affect other properties. “The challenge is trying to balance those ingredients and manage all the expectations of the fabricator and the end user, because there are always tradeoffs,” says Crump. “The formulation concepts leading to a coating with really good spray characteristics are not necessarily the best in terms of compliance with VOC/HAP requirements. In fact, they go in opposite directions.”