Barrier-coat problems require extended fix

In the spring of 1995, Marci and I bought our 1969 Hinckley 38, Kotchka. The survey revealed the hull had modestly high moisture content. The worst readings, on the A-scale of the Sovereign meter, were in the 18 range. These numbers were concentrated in a band two to three feet under the waterline, amidships. It’s worth noting this is where the integral water tanks are located. Fortunately, we had minimal blistering (cosmetic only) and no delaminating. The drying-out process took just over two months.

We contracted out the removal of the existing antifouling paint. The yard used a sandblasting-like process with baking soda as the medium. Once the antifouling was removed, we discovered the gelcoat was very thin or non-existent. Over the boat’s near 30 years of existence, most of the gelcoat had been sanded off. Therefore, the yard suggested we apply a coat of Interprotect 1000 to seal any exposed glass fibers. This initial, clear epoxy coat was sanded thoroughly after drying. The application of the barrier/antifouling paint was next, over a three-day period. We applied six coats of the Interprotect 2000 barrier paint. This paint is applied according to a very specific schedule determined by time and temperature. You do not sand between coats. The antifouling paint is applied to the tacky surface of the last coat of Interprotect 2000. At the time, we believed the barrier coat would give us virtually lifetime protection from water intrusion, damage, delaminating and further blistering. This was not to be the case.

For our first four years with Kotchka, we sailed in Maine, launching in mid-May and hauling in late September. In May of 2000, we moved aboard full-time and set off voyaging. Our first year we sailed the eastern shore of Nova Scotia, Prince Edward Island and the Bahamas. In year two, we returned to Maine, then continued our exploration of the Bahamas. During our second season, we discovered the barrier coat we had applied seven years before had started to fail. Several sections of the barrier coat, about softball size, had lifted from the bottom, exposing the bare hull. Although we originally planned to continue down-island to the Caribbean, we instead opted to return to the United States to deal with the problem.

We arrived in Chesapeake Bay in early May and had Kotchka hauled at Yankee Point Marina, located just off the Rappahannock River. Several more sections of barrier coat had flaked off the hull. We let the boat sit on the hard for three days before we borrowed a Sovereign meter. The readings showed the hull was saturated, in the areas where the barrier paint had failed, as well as the rest of the bottom. However, the yard advised us that Kotchka’s ablative antifouling paint could produce false readings. So, the next step was to remove the antifouling paint. Yankee Point — and many other yards — does not use the baking-soda method. We investigated various chemical strippers but decided to have the yard dry-scrape the paint off. After 60 working hours, several carbide scraper blades and Tyvek suits later, the paint was off.

In retrospect, we could have done the job a bit quicker and cheaper using a chemical stripper. You need to take extra care to make sure all the chemical stripper is cleaned before applying any paint. Disposal of the waste material is another significant issue.

Now the bottom was clean of antifouling paint, but most of the barrier coat was more or less intact. The moisture readings, however, remained high. Just below the waterline, the readings were in the high teens to 20 range. Two to three feet down, the readings were 20 to 25, while at the low point of the hull, the levels were off the scale at 25 plus. We also discovered a large number of hairline fractures in the barrier paint. New fractures continued to appear almost every day. Further investigation revealed a bonding problem between the initial coat of Interprotect 1000 and the hull. We discovered that we could insert a small knife between the barrier paint and the hull, along a fracture in the paint, and easily scrape off the barrier coat. We decided we should grind off the barrier paint wherever we found this bonding/fracturing problem. We used a variable-speed rotary sander with a soft pad and 80-grit sticky-back paper. As we worked away, however, we soon realized we had to remove all the barrier paint, as the bonding problem was widespread.

Reflecting on our original application, we feel four possible problems led to this bonding failure:

  • The baking-soda blast may have left a residue that interfered with the chemical bond created by the Interprotect 1000.

  • Although we did sand the hull after the baking-soda blast using a vibrating palm sander and 80-grit paper, we may not have been thorough and/or not changed the sandpaper often enough.

  • It’s also possible there was a problem with the Interprotect 1000. The material was very thick, almost gooey in texture. When dry, the surface had an orange-peelish look that was very hard to sand and then fair.

  • The barrier-paint system may simply have been left on too long. We were advised by Interprotect that seven years is pushing the limit on barrier-coat products.

    After six weeks on the hard, we finally had a clean hull, but the moisture levels were still high. The levels just below the waterline had fallen to the 10 to 12 range, near ready to paint. The rest of the bottom, however, was still in the 15 to 20 range. We took weekly moisture readings at regular points across the bottom, writing the numbers directly on the hull surface. This way we could see the progress at a glance.

    We needed to invent our own creative methods to speed the drying process. The lower level of the bottom was almost always in the shade because of the way the boat was oriented to the sun. We attempted to divert the sun’s rays by placing reflective Mylar blankets on the ground. It was very obvious this made the bottom significantly brighter from the reflected sun. Using a digital temperature gauge, we discovered the Mylar blankets increased the hull temperature 10� to 15�. It seemed to be doing something. We also thought to dam the through-holes in order to divert water from our sink and drainage holes away from the hull. We used duct tape and hoses. Every little bit helps. Finally, on advice from The Hinckley Co., we rinsed the hull every three to four days with fresh water. The water stuck in the hull was, of course, salt water. Since salt retains water, a regular freshwater rinse accelerated the drying process. The regular rinsing also removed any osmotic fluid that migrated to the surface. We also scrubbed the hull regularly with soap and water to clean off any contaminants.

    Finally, after 16 weeks of drying in the Virginia summer, Kotchka seemed ready to paint. The moisture readings fell to twelve or lower across the bottom. Above the waterline, the moisture readings on Kotchka ranged from five to nine. No matter how long we dried the bottom, the readings would never fall below the topside numbers. The differential is as relevant as the raw readings from the Sovereign meter.

    Before we could apply the new barrier paint, however, we had another challenge. The hull had hundreds of pin-sized holes. Air bubbles in the original lay-up most likely caused these voids. These all needed to be filled, as the voids would be paths for further water intrusion.

    We finally began the process of reapplying a new barrier-paint system. We opted for a system from Ameron/Devoe Coatings, which consisted of a primer coat, followed by two coats of a high-build epoxy paint, followed by two coats of a harder epoxy product. After that came four coats of an ablative antifouling paint. Like the Interprotect system, the Ameron/Devoe paints were applied according to a time and temperature schedule without sanding between coats. The Ameron/Devoe system uses different colors for the barrier paints, making the application easier than with a single-color system, like the Interprotect 2000. When applying the first coat of primer, we noticed we missed some of the pin-sized voids. These we filled with some thickened epoxy barrier paint carefully applied with a small knife. The results look terrific, and we are hopeful they will be a significant improvement over our efforts of eight years ago.

    Marci and J Kolb live and voyage aboard their Hinckley 38, Kotchka.

  • By Ocean Navigator