Stress cracks, dock dings and other mi­nor in­juries aren’t dif­fi­cult to re­pair your­self. Any­thing big­ger? Here’s some info to help you de­cide when to call in a pro. By Mike Smith

Power & Motor Yacht - - IN THIS ISSUE -

Stress cracks, dock dings and other mi­nor in­juries aren’t too dif­fi­cult to re­pair your­self. Here’s how.

Un­less your boat lives her life dock­side cud­dled up to a cou­ple of fend­ers, she’s go­ing to get a few scrapes and bruises. And al­most ev­ery fiber­glass boat, even the most mol­ly­cod­dled, even­tu­ally suf­fers the heart­break of spi­der-web and/or stress cracks. These scars of a life well-lived are un­sightly, but usu­ally are just cos­metic. Gen­er­ally, re­pair of mi­nor dam­age is within the me­chan­i­cal ap­ti­tude of most skip­pers. DIY’ing these small, but time-con­sum­ing, jobs will save big bucks at the boat­yard, too.

But what about big­ger, more se­ri­ous in­juries? I strongly ad­vise against DIY if there’s a hole punched through the side of your boat, a deep im­pact crater re­veal­ing torn fibers or, even worse, cor­ing, or any se­ri­ous dam­age to the lam­i­nate it­self. These are, I’d say, jobs for the pros. Take the time, fork over the cash and have it done right. My rule of thumb is, if I have to buy new tools to do the job, I don’t. I suck it up and pay the money.

First, Do No Harm

Stress cracks and craz­ing them­selves aren’t usu­ally struc­turally dam­ag­ing, only un­sightly; left un­treated how­ever, they can even­tu­ally let wa­ter seep into the lam­i­nate and maybe do real dam­age over the years. Ditto for mi­nor dings and gouges. If the un­der­ly­ing lami-

nate isn’t dam­aged—show­ing bro­ken strands of fab­ric or cracked resin, for in­stance—many skip­pers just leave things alone. But are you sure the cracks and craz­ing are only cos­metic?

M. Boyd Siegel is as­sis­tant crafts man­ager at Saun­ders Yacht­works in Gulf Shores, Alabama, and he’s also aces at fix­ing fiber­glass lam­i­nates. Some­times it’s hard to tell how se­ri­ous the dam­age is, Siegel says. “Gel­coat fail­ure of­ten shows as sin­gle small cracks or craz­ing, er­ratic cracks that are rather shal­low. Lam­i­na­tion fail­ure will show con­cen­tric frac­tures that ra­di­ate out­ward from a cen­tral point of im­pact.” Both is­sues can look sim­i­lar, and the only way to be sure is to open up the dam­aged area and look at the base lam­i­nate.

“Open­ing up” usu­ally means grind­ing with 60- or 80-grit abra­sive disks. In skilled hands, an angle grinder makes short work of re­mov­ing dam­aged gel­coat and fiber­glass, just enough and no more. That’s where many DIY’ers run afoul. They take off too much, and any­thing that comes off has to be put back on, turn­ing a small job into a big one. The rule of thumb is to grind out a crater around the dam­age with a 12:1 slope, cre­at­ing an am­ple bonding area for the re­place­ment fab­ric. For ex­am­ple, an im­pact gouge 1/4-inch deep would mean a 30-inch ra­dius, or a crater 6 inches across. Grind­ing to a 3/8-inch depth in­creases the di­am­e­ter to 9 inches, with 2.25 times the area. That means more than twice as much fab­ric will be needed to fill the crater, twice as much resin, twice as much

squeegee-ing, twice as much gel­coat, twice as much fair­ing, sand­ing and buff­ing. Get the idea?

Un­less you have a close re­la­tion­ship with your angle grinder, I’d hire a fiber­glass pro from the yard to do the grind­ing, if not the whole job; he’ll also have his own tools and safety gear, which you prob­a­bly don’t. (Wear a res­pi­ra­tor, eye pro­tec­tion, long sleeves and gloves when work­ing with fiber­glass, by the way. The grind­ing dust won’t do your lungs any fa­vors, and the ace­tone, styrene and other sol­vents aren’t so great, ei­ther. A sim­ple dust mask isn’t enough.)

Ex­perts rec­om­mend us­ing a Dremel or Dremel-style ro­tary grinder to open stress cracks prior to fill­ing. While eas­ier to han­dle than a honkin’ big angle grinder, a Dremel can cut through eggshell-thin gel­coat and go too deeply into the lam­i­nate un­der­neath if not wielded gen­tly. If you have lots of cracks, get friendly with the Dremel. You can buy one that’s fine for gel­coat work for un­der $100. To fix iso­lated stress cracks, how­ever, I’d take the ad­vice of the folks at West Sys­tem and use a sim­ple can opener and sand­pa­per to widen the cracks. While you might make the same mis­takes with hand tools as you would with power, you won’t make them as fast.

What About Resin?

Shal­low gel­coat cracks with un­dam­aged lam­i­nate un­der­neath can be filled with gel­coat alone. Brush it on, or drib­ble it into the crack with the same pop­sickle stick you used to mix in the cat­a­lyst. But most re­pairs will in­volve resin—polyester, vinylester or epoxy. It wasn’t long ago that the only choice for most of us was polyester; that’s what ma­rine stores car­ried. And polyester worked pretty well. Now it’s easy to buy any resin. But which one is best?

Tra­di­tional wis­dom says to match re­pair resin with the orig­i­nal (i.e., what­ever the boat was built with), but in this case tra­di­tion is be­hind the times. Most boats are still laid-up with or­tho- or isoph­thalic polyester, but fre­quently there’s a layer of vinylester, a hy­brid of polyester and epoxy, right be­hind the gel­coat to im­prove os­mo­sis re­sis­tance. Maybe it gets ground off dur­ing the re­pair, or maybe not. And some higher-end boats are built en­tirely of vinylester. Vinylester resin sticks fine to polyester, so maybe that’s the choice? Nope—it’s eas­ier than that. One resin fits all, and that’s epoxy. It’ll stick to al­most any­thing, and has other ad­van­tages, too.

“While vinylester and polyester both have their places in ves­sel re­pair, any chance I get I will use epoxy,” says Siegel. “Epoxy may be more ex­pen­sive, but it’s a far su­pe­rior resin.” Re­pairs don’t use mass quan­ti­ties of resin, so the ex­tra cost will more than pay off in a higher-qual­ity job, he adds. Epoxy is also more user-friendly, es­pe­cially for the DIY’er. It can be mixed with slow-cure ac­ti­va­tors to ex­tend work­ing time, and fillers to make a thick ad­he­sive putty or an easy-to-sand fair­ing com­pound. “Us­ing the proper fillers, glass and ac­ti­va­tors can re­ally help an in­ex­pe­ri­enced do-it-your­selfer turn out a nice, pro­duc­tion-strength re­pair,” says Siegel.

When you surf the web for in­for­ma­tion on fiber­glass re­pair, you’ll surely come across cer­tain “ex­perts” warn­ing that polyester gel­coat won’t stick to epoxy. Not true, ac­cord­ing to the folks at West. As long as the sur­face is prop­erly pre­pared, gel­coat will stick fine to epoxy. But you must first re­move its “amine blush,” a waxy com­pound that forms on the sur­face of the epoxy dur­ing cure. It scrubs off eas­ily with wa­ter and an abra­sive pad. Polyester resin should be cleaned the same way af­ter cure, to re­move wax that floats to the sur­face to seal out air and al­low full cure. Lam­i­nat­ing resin doesn’t have wax, so it stays tacky, an ad­van­tage when build­ing up lay­ers of fab­ric. If re­pair­ing fiber­glass with polyester resin, be sure to buy it with wax, or else you’ll have to seal it some­how to make it cure all the way; usu­ally, “cures tack-free” will be some­where on the la­bel. If you used the wrong resin and need to seal it, plas­tic wrap works, or you can spray it with polyvinyl al­co­hol (PVA). It’s easy to re­move once the resin has cured. Same thing with gel­coat: It comes with or with­out wax. For re­pairs, you want it waxed.

An Eye for Color

The Achilles’ heel of many re­pairs is match­ing new gel­coat to old. With luck you can buy the cor­rect color from the boat­builder or an af­ter­mar­ket sup­plier; oth­er­wise you’ll have to get a set of pig­ments and tint the gel­coat your­self. I have no eye for color, so for me this means lots of trial and er­ror. Siegel ad­vises mak­ing it eas­ier by first

clean­ing and pol­ish­ing the area you’re try­ing to match, re­mov­ing any grime or ox­i­da­tion; then add small amounts of tint to the gel­coat. Keep track of how many drops of this color and that color you’re adding, so you can mix it again for the next re­pair job. Go slow—a lit­tle pig­ment goes a long way.

When you’re close to a match, daub a thin layer of un-cat­alyzed gel­coat on the ex­ist­ing sur­face and let it dry. “Gel­coat color will change slightly as the sol­vents evap­o­rate; it typ­i­cally tends to get slightly darker,” says Siegel. A sunny day makes this hap­pen faster, and the un-cat­alyzed gel­coat will wipe off with sol­vent. Once you have a match, cat­alyze the gel­coat and ap­ply it to the re­pair. Pros will spray it on, but DIY’ers usu­ally brush; there are brush­able gel­coats on the mar­ket that can be used right out of the can, with­out thin­ners or ad­di­tives. Ei­ther method in­volves plenty of wet-sand­ing and buff­ing to get that new-boat shine.

Man, is this stuff com­pli­cated or what? Isn’t there an eas­ier way, short of do­ing noth­ing at all? Siegel con­cludes, “There are al­ways easy fixes, but they typ­i­cally come at a cost. How long will the re­pair last? One day or twenty years? It all de­pends. The best way is to grind and start fresh.”

If re­mov­ing old, dam­aged ma­te­rial and re­plac­ing it with new is the only way to en­sure you don’t have to re­pair the same place twice, maybe it’s bet­ter to tap a pro­fes­sional and just pay once.

If the re­pair you’re con­tem­plat­ing re­quires large swathes of fiber­glass fab­ric, it may be time to call in the pro­fes­sion­als!

Stress cracks around stan­chion bases are of­ten com­pres­sion-re­lated.

Most DIY angle grinders are elec­tric. This one is a pro-grade pneu­matic.

A ma­jor color-match­ing re­pair calls for both ex­pe­ri­ence and artistry.

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