Required drying time is another factor in gel coat formulation. Several of Interplastic’s customers produce composite parts (bath/shower units, transportation panels, etc.) using high throughput, continuous processes such as conveyor lines. “The gel coat has to be ready to laminate in less than 15 minutes. If it’s not, the production rate of the entire process is reduced,” Crump says. Boat builders, on the other hand, can allow gel coats to cure for much longer intervals.

Designs for End Customers

For owners of boats, RVs, tub surrounds and other end users, the priorities are durable gel coats that keep the desired high-gloss appearance for as long as possible. They don’t want to see blotchy colors or a chalky finish.

“The level of expectation has gone up; we’re making larger, more expensive, more high-end boats, and the customer wants them to retain that aesthetic as long as possible,” says Ryan Wilkins, North American marine gel coat product manager, Ashland.

Longevity is not the only end user requirement, however.

“There’s adjustment and adaptation depending on where the product is going to be used,” Certain says. “For example, a transportation product doesn’t see as much water exposure as a marine product, so we can compromise a little on the water resistance but work very hard for UV resistance for that market.”

A cultured marble sink top with a gel coat finish won’t have problems with UV exposure, but will need to withstand thermal expansion and contraction caused by hot and cold water running over it. A wind blade on an energy-producing turbine may move at 300 mph, so its gel coat needs to have excellent abrasion and fatigue resistance as well as outdoor durability, including resistance to heat, light and moisture.

End customers have challenged gel coat manufacturers with their demands for a greater variety of colors with more depth and intensity. Black and other dark colors are popular with manufacturers of personal watercraft, for example, but developing the gel coats that maintain those colors over several years is difficult.

Style trends also impact gel coat formulations. Years ago, metal flake finishes were popular in the bass boat market; now, consumers want boats with a look that emulates today’s automotive finishes, which have very tiny flecks that reflect light.

When designing for the transportation industry, gel coat manufacturers have a different challenge. Truck rental and RV companies that use FRP wood panels for their vehicles’ sidewalls want the same color and finished look for the composite portions of their trucks as for the metal sections.