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Barrier coating is bulwark from damage

Knowing what to use and when to use it can add life to your hull and prevent problems such as blisters

Knowing what to use and when to use it can add life to your hull and prevent problems such as blisters

When Fred Barsch looks at the bottom of his 46-foot Hatteras every spring, it’s with a mixture of pride and minor irritation. Nine years ago he did a blister and barrier coat job, and he did it right. Unfortunately, adhesion problems with the anti-fouling paint developed later, which he attributes to overapplying the paint rather than a poorly prepared barrier-coat surface.

“The yard kept telling me to apply more paint,” Barsch says. “But Interlux said I could go for three years before applying the next coat. I should have listened to them.”


 One of the key recommendations from a study of hull blisters was applying a barrier coat.

Barsch, 52, an electrical contractor from Wading River, N.Y., says he’s got about six layers of paint on the bottom, and the few sections of the hull where the paint likes to peel are nothing compared to what he found in January 1999. During a routine hull inspection he saw “wet spots” in the bottom paint. “I knew something was wrong,” he says.

The following March, Barsch paid the yard to sandblast the hull. “There were thousands of little holes,” he says. “At first I was shocked seeing them.” His shock diminished when exploratory surgery showed that the blisters weren’t deep, and readings from a moisture meter showed that the hull was dry. A stickler for doing projects right, Barsch didn’t think the yard would take the time to properly grind and fill every blister, so he decided to do the job himself, including application of the barrier coat. “It was a quality-control thing,” he says.

Barsch’s boat, Pristine, was built in 1976 — prime time for hull blisters. The overwhelming majority of fiberglass boats from the 1970s and ’80s were built with polyester resins that are highly susceptible to moisture penetration, which leads to osmotic blistering that can eventually damage the hull. Howls from angry boat owners and some high-profile cases where blisters compromised the structural integrity of hulls prompted the Coast Guard to fund a blister study. The American Boat Builders and Repairers Association also put up money.

The University of Rhode Island’s chemical engineering department began the study in 1985, and the research indicated that fiberglass acts like a sponge, slowly absorbing water over time until a chemical reaction occurs that causes blisters. One of the key study recommendations was the application of a barrier coat to prevent blisters, or at least reduce the risk that they might develop. Paint manufacturers began producing epoxy barrier coat products — Interlux, for example, introduced its Interprotect barrier coat line in the mid-’80s. And WEST SYSTEM’s two-part epoxy in conjunction with 422 Barrier Coat Additive was, and remains, effective for use as a barrier coat.

For years yard crews and do-it-yourselfers like Barsch busily applied barrier coats, usually after a full-out assault on pesky blisters. “In the 1980s and 1990s, we were doing dozens and dozens of barrier coats every year because boats built in the 1970s and 1980s had a lot of problems with osmotic blistering,” says Rives Potts, manager of Brewer Pilots Point Marina in Westbrook, Conn. “But in my experience a lot of these problem boats have already been fixed, so we’ve seen fewer boats coming in with blisters than in the past.”

Then and now

Applying a barrier coat in the bad old days when the products were relatively new was no easy task. Pot life — the amount of time before the epoxy begins to set — and maximum dry time between coats was pretty short, much shorter than it is now.

“When we first came out with [Interprotect] it had a very fast solvent, methylene chloride, which had only an 18-hour max dry time between coats. So that was tough if the weather turned on you and you had to get the job done,” says Jim Seidel, Interlux assistant marketing manager for North America in Union, N.J. “I had guys putting on coats at 2 a.m. to keep up with the schedule, and that wasn’t a happy thing.”

About 12 years ago, Interlux switched from methylene chloride to xylene, which is less harmful to the environment and adds to pot life and dry time. It also makes spray applications possible, something boatyards wanted, Seidel says. Interprotect 2000E has a maximum two-week dry time between coats, a far cry from 18 hours.

The WEST SYSTEM barrier coats also have become easier to apply. “We have more hardeners than we did before that give more working time,” says Tom Pawlak, technical adviser for WEST SYSTEM, of Bay City, Mich. “If you want to get six coats on in a day, you can use our Fast Hardener. On a 70-degree day you’ll only have to wait about two hours between coats.” Pawlak adds that most people wait too long between coats, saying the epoxy can be “like the sticky side of a roll of tape or even like fly paper” when you apply the next coat.

It took time, but boatbuilders eventually got wise and started using better construction techniques and materials. Blisters haven’t gone the way of the dinosaur, but they are less common today. Barrier coats applied at the factory or as a preventative measure for older boats are more the norm, rather than the icing on the cake after a big blister job.

“We’ve got an even split between preventative barrier coats and blister repairs,” says Potts, adding that Pilots Point Marina does about a dozen or so barrier coats on new boats every year.

Barsch bought a Regulator 26 in 2001 and applied a barrier coat before launching the boat for the first time. He notes with a laugh that he followed Interlux’s instructions and hasn’t had any adhesion problems with his anti-fouling paint.

Bone-dry the only way

If you’ve just bought a new boat and it doesn’t have a barrier coat, the decision to apply one is a no-brainer, as long as you haven’t applied bottom paint. The hull will be dry and will stay dry with a barrier coat, and a few simple steps will remove from the surface any wax or mold release that will interfere with adhesion. Prepping the hull — the hardest and most time-consuming part of a barrier coat job — will be minimal. However, Potts cautions against doing anything until you carefully read the hull warranty.

If you have an older boat without a barrier coat, the decision to apply one is more complicated. WEST SYSTEM’s Pawlak warns that barrier coats can sometimes do more harm than good because they can trap moisture. “You’re creating a torture chamber,” he says. “Barrier coating over problems is the biggest mistake we see.”

He adds that older boats with no obvious blisters may still be wet, and applying a barrier coat in those cases is just asking for trouble. “If there’s moisture trapped in the hull, the barrier coat will fail,” Pawlak says. Correcting the problem requires doing the entire job over again, making sure that the hull is dry. “Often people remove all the gelcoat, and sometimes you have to go even deeper to get to dry laminate.”

Before applying a barrier coat on an older boat, Potts says grinding away small areas of gelcoat about 4 inches in diameter all over the hull is a good idea, because it will expose the laminate for testing with a moisture meter. Some parts of the hull can be bone-dry, while others can contain moisture. Any areas where moisture is found must be sanded to dry laminate, according to Potts. There’s no need to re-apply gelcoat, since you’re going to apply a barrier coat.

Wetting down the laminate with acetone is another test, Pawlak says. “If you see white strands of fiberglass, that’s a sign of wet laminate,” he says. “You want the laminate to look dark.”

The bottom line is the hull must be dry, says surveyor Bob Turner, a partner in Kelsey & Turner Surveys, of Annapolis, Md. That’s why he recommends doing barrier coat jobs in the spring rather than the fall after hauling out. Hulls dry out over time, the longer the better. “I sometimes get calls from boat owners about to do a barrier coat job who want the peace of mind knowing that the hull is really dry,” Turner says. “They know what’ll happen if it isn’t, and it’s not pretty.”

Moisture meters will give good results, he says, but you have to know how to interpret the readings. Vinylester resins read differently than polyester and epoxy resins. Graphite-based and high-copper paints will set the meter off, sounding a false alarm that could end up costing lots of money.

Turner uses an Electrophysics GRP 33 marine moisture meter. On a scale of 0 to 30, a reading of 10 to 12 would be quite dry. A boat fresh from the factory should give readings of 4 to 7. “I start getting concerned that the laminate is reacting [to moisture] when I see readings of 14 to 16,” Turner says. “That’s where I’ll turn to a customer and suggest doing a laminate profile.”

Digging in

Assuming the hull is dry and you’re ready to go, the first step in the barrier coat job involves removing all the anti-fouling paint. Potts likes to sand, saying it is the most efficient so long as the paint isn’t too thick. Otherwise, chemical strippers or sandblasting is the way to go, he says.

“The real hard part is taking off the anti-fouling,” says Interlux’s Seidel. “You can try to sand it off, but you can dig into the gelcoat. The safest thing is to use a chemical stripper. These are typically slow acting and fairly expensive. A lot of people opt to have the bottom sandblasted, but you’ve got to make sure the operator has a lot of experience with boats.” Sandblasting can do a great deal of damage, Seidel warns, saying that a soft blast bead like baking soda or ground-up corncobs is good.

After the anti-fouling is off, the hull prep involves filling voids and cracks, and sanding to abrade the surface to ensure proper barrier coat adhesion. Application is temperature-sensitive. Pot life decreases as ambient temperature and humidity increase. Pawlak and Seidel both say the ideal day for a barrier coat job will have low humidity with temperatures around 70 degrees. There is wiggle room, but hot days will mean scurrying to apply each coat within a much shorter application window.

More thin coats are better than fewer thick coats, says Seidel. “It usually takes four coats to get to the 10-mil thickness we recommend,” he says. “Just roll it on like anti-fouling paint using a 5/16- or 3/8-inch nap roller.” WEST SYSTEM recommends five or six coats to attain an 18- to 20-mil thickness.

Both Seidel and Pawlak say a 25-foot sail- or powerboat will require about three gallons of barrier coat. Excluding brushes, rollers, pumps and other materials, the cost for just the barrier paint is around $300.

Hiring a boatyard to do the work obviously is much more expensive because of labor charges. “Our rate for barrier coat jobs is $200 per foot,” Potts says. “The total cost also depends on how much anti-fouling paint we have to remove and if we find blisters. Every case is unique, so asking how much it costs to do a job on a hypothetical basis is a bit like asking how much is it to buy a new suit. It all depends on the suit you want.”

Potts says it makes the most sense to spring for a barrier coat on an older boat when you’re already paying the yard to strip all the old layers of bottom paint, which must be done from time to time. “The biggest cost of the process is stripping the paint off and prepping the hull,” he says. “When you’ve spent the money to get rid of the old paint, it seems to us to be bad value to go cheap at that point and not spend the extra money to apply a barrier coat. You can either do it really right, or you can cut corners, which can come back to grab you later on.”

Most of the money you spend on improvements isn’t recouped when you sell the boat, but a barrier coat on an older boat is viewed as a positive from a buyer’s standpoint, says Greg Kaufman, a broker at Martin Bird & Associates in Annapolis, Md. “One of the first things buyers ask about older boats is the condition of the bottom. If a barrier coat has been applied, it enriches the whole package. It’s more of a negative if it hasn’t been done,” Kaufman says.