Passage Maker - - Trou­bleshooter -

Fi­nally, you must con­sider whether the in­stal­la­tion will be above or be­low the wa­ter­line. Each prod­uct type strikes a bal­ance be­tween strength, flex­i­bil­ity, and re­sis­tance to chem­i­cals and UV rays.

Ad­he­sives max­i­mize strength. If you in­tend to never sep­a­rate the parts, a high-strength ad­he­sive can be ap­pro­pri­ate. We have lifted sail­boats, re­moved all the keel bolts, and looked on as 12,000 pounds of lead held fast to the boat be­cause of the ad­he­sive. In other words, use a high-strength ad­he­sive when you con­sider the bond to be per­ma­nent.

Sealants typ­i­cally pro­vide greater elon­ga­tion than ad­he­sives and lower strength. An ideal sealant will ex­pand and con­tract with changes in tem­per­a­tures and move­ment of the parts. A stain­less rub strake will ex­pand at a dif­fer­ent rate from the wooden or fiber­glass rub rail be­neath it. If the ex­pan­sion rates ex­ceed the elas­tic­ity of the sealant, the ma­te­rial will break down and wa­ter pen­e­tra­tion will soon fol­low.

Caulk­ing com­pounds have mod­er­ate ad­he­sion, good elas­tic­ity, and high chem­i­cal and UV re­sis­tance. Un­like sealants and ad­he­sives, caulked seams re­main ex­posed to the el­e­ments as well as other is­sues such as boat clean­ers and UV rays.


These com­pounds will be avail­able in an ar­ray of com­po­si­tions with vary­ing bal­ance be­tween strength, flex­i­bil­ity, and re­sis­tance to chem­i­cals. The fol­low­ing list gen­er­ally pro­gresses from low­est ad­he­sion to high­est:


Sold in a roll with re­mov­able film on one side, butyl has the low­est strength and high­est elon­ga­tion. Some cruis­ers swear by it—butyl is easy to ap­ply, re­quires min­i­mal cleanup, and pro­vides great elas­tic­ity. On the other hand, butyl re­mains sticky and at­tracts dirt. And although you can avoid the squeeze-out and cleanup rou­tine of the other sealants, the edges of the butyl must be trimmed and can of­ten look a lit­tle un­even.


Pro­vid­ing high elas­tic­ity over long pe­ri­ods and through a wide range of tem­per­a­ture vari­a­tions, sil­i­cone has a strong re­sis­tance to chem­i­cals, is UV re­sis­tant, and is easy to ap­ply. It can­not be painted, how­ever, and when clean­ing up you can con­tam­i­nate the sur­round­ing area (which can com­pli­cate paint­ing or var­nish­ing). Sil­i­cones come in two va­ri­eties: neu­tral cure and acid cure. Acid cure is eas­ily iden­ti­fied by its strong vine­gar-like odor, while neu­tral cure has al­most no smell. Neu­tral cure is pre­ferred as it ad­heres more re­li­ably. We have had good re­sults for many years in our boat­yards with GE SCS2000 SilPruf, and an abun­dance of other good choices can be found on the chan­dlery shelves.

The ar­ray of sealant choices at Fish­eries Sup­ply in Seat­tle. Your lo­cal marine sup­ply store will of­fer a be­wil­der­ing ar­ray of choices. It pays to un­der­stand the dif­fer­ences and how they re­late to your sit­u­a­tion.


For many years poly­sul­fides were the go-to ma­te­rial for sealants. Poly­sul­fides main­tain their bond well and have very good chem­i­cal re­sis­tance, which I can at­test to hav­ing tested its lim­its as a young sum­mer hand on a boat with a teak deck. The owner in­sisted on freshly bleached decks with a beau­ti­ful gold hue. We kept push­ing the en­ve­lope with the deck bleach un­til one day I saw him stand up af­ter sit­ting on the deck and no­ticed black stripes on his white pants from the seam com­pound. All prod­ucts have their lim­its. Poly­sul­fides cure slowly and should not be used with Plex­i­glas, Lexan, and many other plas­tics. BoatLIFE Life- Calk has been around for many years and has proven it­self in a wide va­ri­ety of ap­pli­ca­tions.


These polyether prod­ucts are rel­a­tive new­com­ers. They are very ef­fec­tive for caulk­ing beads as they are non-yel­low­ing white com­pounds with high UV and chem­i­cal re­sis­tance and can be

painted. Polyether is fairly tena­cious and should be thought of as more of an ad­he­sive. It works well with some plas­tics, and 3M 4000UV is a good ex­am­ple.


Also more ad­he­sive than sealant, polyurethanes do not re­sist chem­i­cals as well as sil­i­cone dones and can­not be used with most plas­tics. The pre­vi­ously men­tioned 3M 5200 pro­vides the most per­ma­nent ver­sion of these prod­ucts. 3M 4200 of­fers a more mod­er­ate ad­he­sion strength, while Sikaflex-291 works well for low-strength ap­pli­ca­tions.

As with all things boat­ing, folks will ar­gue for their proven ma­te­rial or method. Be­fore we get into some ap­pli­ca­tion de­tails, I’d like to ad­dress two of my pet peeves on this sub­ject. The first comes down to sealant ver­sus ad­he­sive. If the hard­ware you are bed­ding will be held in place with sub­stan­tial metal fas­ten­ers, then you should not be us­ing any­thing more than a low-ad­he­sion prod­uct. Even­tu­ally you will want to rebed that item and re­moval should not in­clude de­stroy­ing the fiber­glass.

Some will ar­gue for ap­ply­ing sealant to the fas­ten­ers and leav­ing the hard­ware it­self dry. Pic­ture that stain­less rub strake men- tioned ear­lier—bed­ding the en­tire length will re­quire more time, more sealant, and a lot of cleanup. As the ar­gu­ment goes, leav­ing the back with­out sealant will al­low any wa­ter that gets in to drain out. I’m not a fan of that ap­proach. The con­tin­ual ex­po­sure to salt wa­ter of­ten leads to stain­ing and dis­col­oration of the metal, which then bleeds onto the sur­round­ing area. I pre­fer to see metal at­tached to fiber­glass with a healthy film of sealant be­tween the two.


While we have just noted that ad­he­sives, caulks, and sealants all serve dif­fer­ent func­tions, for sake of sim­plic­ity we will use the term “sealant” to re­fer to all three types when dis­cussing their ap­pli­ca­tion as they re­quire sim­i­lar con­sid­er­a­tions.

If the sur­faces are glossy, scuff them up with some sand­pa­per to pro­mote ad­he­sion. Both sur­faces should be cleaned be­fore ap­ply­ing the sealant. Wip­ing with de­na­tured al­co­hol works well. Dry-fit the in­stal­la­tion and then mask around the perime­ter with 2-inch tape. Ap­ply the sealant lib­er­ally to one of the mat­ing sur­faces. In ad­di­tion, make sure you get some sealant on the un­der­side of the fas­tener head and on the por­tion of the shank that passes into the hard­ware and the struc­ture. Now tighten it all up and al­low the ex­cess ma­te­rial to squeeze out onto the tape.

Sealant should squeeze all the way around the perime­ter—that’s your as­sur­ance that the en­tire sur­face has been coated. If you are us­ing slot­ted head fas­ten­ers and you want them lined up, now is the time.

Once you have fin­ished tight­en­ing the hard­ware, it’s cleanup time. Sol­vent mat­ters and you must pay at­ten­tion to the la­bel in­for­ma­tion. Some prod­ucts will spec­ify min­eral spir­its; oth­ers will call for al­co­hol. Choos­ing the wrong sol­vent for cleanup can ruin the sealant.

Some prod­ucts can be pur­chased in a fast cure or slow cure ver­sion. If you are work­ing in the heat of sum­mer and in­stalling a more com­pli­cated com­po­nent, such as a wind­lass, the slow cure will give you more work­ing time.


All sealants have a life­span, but that span de­pends on the prod­uct, the ap­pli­ca­tion, and the amount of ex­po­sure to UV, chem­i­cals, and abra­sion. The sealant un­der a sea­cock, for ex­am­ple, will last two or three times as long as the seam com­pound in a teak deck. Ten years would be a rough guess for deck hard­ware, but how do you know it’s time? Leaks pro­vide an ob­vi­ous in­di­ca­tor, but not all leaks can be de­tected as they of­ten leak into the core. Check­ing the deck and cabin with a mois­ture me­ter every few years can save you tens of thou­sands of dol­lars by pre­vent­ing on­go­ing hid­den leaks from sat­u­rat­ing the core ma­te­rial. If the me­ter in­di­cates el­e­vated read­ings around a port­hole or lad­der mounts, it is time to rebed. If one item needs rebed­ding, it prob­a­bly in­di­cates a gen­eral need to deal with all of the hard­ware.

Vis­ual in­spec­tion can be help­ful, too. When the sealant shows cracks and rough­ness it should be re­newed. When you have iden­ti­fied a gen­eral need to rebed hard­ware, you might con­sider a grad­ual ap­proach over a few years. You could deal with the fore­deck and side decks this sea­son, the cock­pit the next, and the fly­bridge two years from now. If you are buy­ing an older boat ( pre- 2000 for ex­am­ple), you should plan on rebed­ding grad­u­ally dur­ing the early years of own­er­ship.

Whether in­stalling new hard­ware or rebed­ding old, choose the sealant thought­fully and clean the sur­faces dili­gently. It might be a mun­dane task, but it will pro­tect your boat’s struc­ture and will elim­i­nate an­noy­ing—and po­ten­tially costly—leaks.

A bead of sealant should be placed un­der the head of each fas­tener.

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