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ITW PLEXUS
ITW Plexus, a unit of Illinois Tool Works and a Fortune 200 company, makes adhesives used for structural bonding of nearly all thermoplastics, metals, and composite materials. What makes Plexus perfect for boatbuilding is its ability to provide extremely durable bonds with little or no surface preparation. Company reps state that the bond is so strong--"the death grip" is how they phrase it--that the fiberglass will delaminate before the bond fails. This was confirmed during a recent interview I had with John Leek, president of Ocean Yachts. "We use Plexus to bond the forward cabin floor on our new 62 Super Sport Convertible," he told me. "During preconstruction testing we were forced to destroy the module when we tried to separate the bond. It just wouldn't let go." Other boat companies using Plexus include Baja and Thunderbird.

According to Plexus, traditional construction methods of bonding deck and hull that use bolts can result in cracking or crazing in the vicinity of the fasteners due to the continuous stress and strain as the boat moves through the water. Deteriorated sea conditions can cause the joint to work even more, but Plexus, the company contends, working with the fasteners, distributes the forces more evenly over the entire deck-to-hull joint.

While Plexus has an extensive range of products that includes all-purpose adhesives, those for difficult-to-bond applications (including metals), and those needing fast and medium cure times, its MA500 and MA550 are most commonly used in FRP construction.

3M
Go into any working boat yard or boatbuilding facility in the world, and you're likely to see spent tubes of 3M's 5200 marine adhesive/sealant lying about. This product's ability to cure tack-free in one hour and fully cure in about 24 hours, along with its extremely strong bonding properties and ability to retain its strength whether above or below the waterline, has made it one of the industry's standards. (A regular-cure formula that dries tack-free in 48 hours and is fully cured in five to seven days is also available.) So much so that such prestigious builders as Viking, Bertram, and Hatteras use it. Resistant to weathering and salt water, 5200 also remains flexible after curing and so accommodates structural movement. 

Developed for the aerospace industry some 30 years ago, 5200 is a modified polyurethane adhesive that differs from other products principally in the strength of its bond. This advantage is due to its chemical makeup and manufacturing process, both of which are proprietary.

"For marine applications it's a bulletproof product," says Tom Dewey, 3M's market development manager. "Besides its structural strength, it has incredible elongation and can stretch 400 to 500 times its original strength before it breaks." It will also cure faster in humid conditions and can be applied to virtually any substrate. Aluminum, however, should first be primed.

Because 5200 is so strong and its primary use is for permanent applications like those in hull-to-deck bonding, 3M introduced 4200, which is about half as strong and is more suitable for general-purpose applications. "If you want to get [the adhesive] off, go with the 4200, says Dewey. "If not, the 5200 is for you."

There's a lot that goes into putting a boat together the right way, and resins and adhesives are principal reasons why modern boats are stronger than their predecessors. And if you have to make a repair, knowing which product to use can make your time up on the hard not only easier, but also more successful. In that way you'll feel a lot better the next time you drop your dock lines and head out.

Gougeon Brothers Phone: (517) 684-7286. Fax: (517) 684-1374. www.gougeon.com.
ITW Plexus/USA Phone: (800) 851-6692. Fax: (978)- 774-0516. www.itwplexus.com.
3M Phone: (877) 251-9046. www.3M.com.

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