Composites Fabrication Magazine
October 2003

BARRIER BUILDING: What Protects Your Hull?
By Bob Anderson

One of the greatest challenges of boat manufacturers is to maintain the aesthetic integrity of the hull throughout the manufacturing process. Inherent in hull construction are chemical reactions that can cause a finish to distort, bubble, and even crack over time. Some major boat manufacturers have begun to apply a barrier coat during construction in order to protect the hull exterior and preserve the boat’s aesthetic appeal.

As the resin layers in a laminate cure, they produce an exothermic reaction, and the continuous shrink that occurs can distort gel coat, causing it to appear bubbled or ridged. This effect is referred to as ”print through.” In a closed molding environment, the added pressure required in the process can exacerbate the effects of heat, causing even more significant print through.

After production is complete, as the boat is exposed to climatic changes like temperature variations, the effects of continuous shrink are amplified by the post-cure process, which makes imperfections on the hull’s surface profile increasingly more pronounced. These additional imperfections may require repair. Often these repairs fall under the boat’s warranty and, therefore, cost the manufacturer time and money.

While the print through alone does not significantly affect a boat hull’s mechanical function, it reduces the aesthetic value of the boat. In the past, many boat manufacturers removed the effects of print-through by sanding down the hull and buffing imperfections in the gel coat to obtain the desired shine. However, this re-work is costly in time and materials. In addition, as they are exposed to sunlight and the elements, re-worked areas can create even more cosmetic imperfections via potential “yellowing.” As a result, many forward-thinking boat manufacturers began to look for ways to improve the laminate’s surface profile during the manufacturing process.

Filled barriers
To address the concern of the manufacturers, several chemical companies researched and developed a concept now known as barrier coats. These barrier coats were specifically designed to protect the surface gel coats from the exothermal reaction produced by curing resin. Shiraz Sidi, Director of Materials for VEC Technology, a subsidiary of Genmar Industries, is responsible for testing all materials for building laminates at each Genmar plant.

“The primary function of the barrier coat is to enhance the blister resistance in the gel coat,” Sidi, who has become a strong advocate of barrier coats, says. “It also acts as a print blocker, giving us much better cosmetics.”

”During production, after the gel coat is applied to the hull mold, the barrier coat is sprayed to a thickness of 25-35 mils. After reaching the necessary cure stage, resin layers are added. As the resin cures, the barrier blocks the heat of the reaction and protects the gel coat against any distortion.

Interplastic Corporation was one of the first companies to pioneer the field with a non-filled barrier coat resin. By 1994, sprayable filled barriers were introduced on a large commercial scale by Magnum Venus Products and ITW SprayCore. In the past few years, large resin suppliers, including Cook Composites, Reichhold and Ashland, have followed suit and started introducing their own spray barrier systems. These sprayable barrier coats are now being used in the production of such well-known boat brands as Crownline, Four Winns, Larson, Stratos and Mastercraft. But, what’s the secret behind barrier coats?