Goop and Goo, and Why I Hate 5200


Recently, while helping member Henning make a decision on which way to go in replacing the seacocks on his boat, we were discussing various options in the comments. All was going along fine with lots of good options being proposed…and then someone mentioned…I have to pause and take a deep breath to repeat this…OK, I can do it…5200, and I saw red.

Yea, I know, it’s available in every marine store and is much loved by some. And I certainly don’t blame the member who mentioned it…but I do hate the stuff.

A Sad Story

Let me tell you why. Back some 35 years ago, I had just bought a new-to-me, but in fact very tired, 45-foot sailboat. And, like most hard-used boats, most every port, hatch and fitting in the boat leaked because working of the hull and time had broken the goop-seal between those hardware items and the hull.

So, like any soon-to-be-demented-refitting-boat-owner, I removed all those fittings and re-bedded them with…wait, I have to pause to collect myself again before saying it…5200. And yes, I followed the directions faithfully.

The task itself went reasonably well, or at least as well as it does for me with any of these goops. (Has anyone else noticed that no matter what you do, five minutes after you take the cap off it’s in your hair, and ten minutes after that it’s on the salon upholstery, even though you are working at the top of the mast? Or is it just me?)

That Got Sadder

I digress…I finally got the whole job done and went sailing and everything was fine…for about a year. And then a good third of those hatches, ports and deck fittings bedded, or in fact not, with 5200 started to leak. Not a lot, just a few drops, and only when there was a lot of water around, but a leak is a leak.

So I started to remove each piece of leaking hardware…or at least tried to. And that’s when I found out about the other characteristic of 5200: it sticks…I mean, it really sticks. To the point that I ruined two expensive hatches by bending them while removing them and actually bent a small pry bar. Not to speak of tearing the gelcoat off the laminate in some places.

I ask you, how can a material both stick like hell and leak? Beats me, but that’s what happened.

Maybe it’s just me. Maybe 5200 works great for everyone else. Maybe I just hurt its feelings with all that colourful language when it got in my hair and it decided to get even.

A Real Problem?

But maybe not. Since then I have spoken with several experienced managers who won’t allow the stuff past the gates of their boatyards because they have had the same sort of experiences.

No, I don’t have any proof that the stuff don’t-work-worth-a-damn, but the gun doth smoke. No tube of 5200 will ever touch Morgan’s Cloud, at least as long as I’m around to protect her from the diabolical stuff.

I really don’t know why 5200 leaked on my old boat. Perhaps it’s not a good idea to have a bedding compound that sticks too aggressively? Perhaps that causes fractures as the boat flexes? I really don’t know. (Do any of you engineers have a theory? If so, please leave a comment, I would simply love to know.)

What I do know for sure is that bedding any fitting with 5200 that you, or some other poor sod, may ever have to remove is a really bad idea, because crowbars will quickly become involved, and maybe explosives too.

A Clue?

Yes, I know about this stuff that purports to break the stiction, but is that really going to work with a large fitting and a lot of 5200? And if it does, that brings up another worry: If the removal stuff is as innocuous as the makers would have you believe, and especially since it’s water-based, what does that tell us?

Maybe the effectiveness of this removal stuff—assuming it is effective, I have never tried it and it was not available when I was rupturing myself—might be the clue to the cause of the leaking problem?


So what do I use instead of 5200? Good old Life-Calk polysulfide, a goop that was once called Thiokol, back in the day when it was developed to patch bullet holes in bombers…in World War II.

Yup, it ain’t new and it ain’t sexy, but I redid all the 5200 bedding that failed on that old boat and never had a leak, and it hasn’t let me down since, above or below the waterline. And while it’s pretty sticky, you can get stuff apart that you bedded with it without too much foul language.

lifeseal_cartridge_white__38775.1377245961.1280.1280Oh yes, one admission, I do use Life-Seal, a combination of silicon and the same chemistry as 5200 (polyurethane) if, and only if, I’m bedding Lexan—for example, the clear plastic in a hatch—and it works well.

Two Warnings

So there it is. Use whatever you like, but if it’s 5200, don’t bring it near me as I tend to react instinctively by throwing it into deep water, and the stuff is expensive and probably a pollutant too.

Also, never tell a boatyard that you are a 5200 user if you are soliciting a quote from them for a job that requires removing even one fitting. If you do, they will triple the price in the hopes that you will take your boat down the road to the next boatyard…the one they hate.

Further Reading


Any one else had a bad experience with 5200…or even a good experence? What goops and goos do you like and why? Please leave a comment.

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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

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62 comments … add one
  • Max Aug 8, 2016, 9:01 pm

    I caught, just in time, a mechanic in a Mexican yard about to 5200 the custom made, impossible to find a replacement for, rubber bellows over the rudder post bearing. The yard manager took him off boats and put him behind the parts desk after that (might not have been his first offense though) .

    Thanks all the great e-books.


    SV Fluenta
    Presently Vuda Point, Fiji

  • Chris Aug 8, 2016, 9:52 pm

    Having heard the horror stories regarding 5200, we avoided the stuff during our refit and went to the opposite extreme-butyl tape. Easy to work with, but doesn’t stick all that well after a while. In the future I think I would go with a polysulfide sealant as written above.

  • Dick Stevenson Aug 9, 2016, 3:13 am

    Hi all, I know of a marine parts distributor who said that he made a mess with 5200 just ordering it on the phone.
    Dick Stevenson, s/v Alchemy

  • Dick Stevenson Aug 9, 2016, 4:38 am

    Hi Chris, John and all
    With regards to butyl rubber as a bedding/caulking material, I have read that not all butyl rubber is the same and have gotten all of my BR from a marine source I trust, (and where there are superb “how to” articles on thru-hulls as well as many other common marine projects). And for the project John is referring to, I am unsure of BR’s use as an underwater bedding/caulk compound. And, Chris, I am not sure what you mean by “doesn’t stick all that well after a while”. Although quite sticky, BR is not to be considered an adhesive.
    That said, I have been using BR for almost all, maybe all, deck bedding/caulking for 6-8 years now and have been very pleased: easy to work, clean, not unattractive in the grey or black. It is my research that it will last virtually forever (and unlike the traditional caulking/bedding, the BR I have had stored in the bilge for years is as good as new, not hard in the tubes-or out of expiry- as 5200 and Life- Caulk etc. would be, especially if opened). One of my earliest uses was to bed chainplates. I am recently replacing my chainplates and I pulled one that was bedded in BR 6+ years ago and the BR looked and felt virtually new to the extent that I was tempted to re-use it (I resisted this unreasonably frugal side of my nature).
    Not any of my BR bedding has failed yet nor shown any signs they are likely to. A fingernail into the edges still shows the BR to be soft and flexible as when new. It is my understanding that most traditional bedding/caulking compounds (polysulfides and polyurethanes) are considered to have a lifespan: they dry out and shrink, and it is recommended that the bedding be re-placed every now and again (10 years comes to mind, read the manufacturer’s fine print). In the scheme of re-bedding portlights, for example, 10 years is not a long time, and not a chore I wish to do even once a decade. And they (I know from personal experience) can leak undetected into a balsa core whereas many leaks are mere nuisance and announce themselves quickly.
    Enough for now: more on working with BR if wished for.
    My best to all, Dick Stevenson, s/v Alchemy

    • Marc Dacey Aug 9, 2016, 12:15 pm

      Dick, the butyl tape I have on my 1973 FG sloop is still pliable, as I discovered after someone collided with me and I had to remove a sterncorner extrusion. I have keep a couple of rolls aboard. As for 5200, while I think it MIGHT have a use in bonding keels to keel stubs, it’s the stopped clock of marine glues. I prefer 4200 where I must prefer it.

    • Alan Bradley Aug 23, 2016, 1:12 am

      Hi Dick,
      I always enjoy reading your comments, lots of good stuff there. I’m looking at re-bedding a couple of ports with BR. Any helpful tips would be greatly appreciated. I’m not sure how to take a discussion like this off-line, but my email is of course included in this comment.

      • Dick Stevenson Aug 23, 2016, 8:30 am

        Hi Alan,
        Thanks for the kind words.
        I am on the road, so have limited time.
        That said, in looking over the stream of comments, I think everything has been covered. The web site Compass Marine mentioned by me and others is a wealth of knowledge and definitely should be consulted. It will give you a feel for the material and what it can do. Not related to BR, but often neglected, if the deck is cored, ensure the core is reefed back and filled with an epoxy slurry well past the bolt/screw holes.
        Let us know how your project works out.
        My best, Dick Stevenson, s/v Alchemy

        • Alan Bradley Aug 23, 2016, 10:59 am

          Hi Dick,
          Thanks for the quick follow-up and thanks for the tip on prepping the core area below the screw holes.
          Best regards,
          Alan Bradley, s/v Vivacia

  • pat synge Aug 9, 2016, 5:04 am

    I haven’t used 3M’s 5200 but have used gallons of various other single component polyurethane sealant/adhesives by Sikaflex and Bostik and have had good results. I’ve just finished glueing down a timber floor onto a (well cured) concrete slab.

    Yes, you have to be careful to avoid making a mess but that’s mostly preparation (good fitting gloves, masking tape, mineral turpentine and lots and lots of rags into a big plastic lined bin). In many situations (decking) it’s best to leave any excess to cure in place and remove it with a blade.

    Usually leaks are the result of over-tightening and squeezing most of the sealant out. It can’t do its job if it’s not there. The right primer is essential with acrylic and polycarbonate.

    It has a specific % of elasticity (depending on the grade) and so if there’s going to be thermal expansion differential (ie with plastic glazing) or movement due to flex you have to allow enough thickness of sealant to absorb this. I usually use a 3mm double sided foam tape as a spacer when glazing.

    Removal of fittings: difficult. It has to be carefully cut to remove the fitting and then the residue carefully removed (ie with a chisel or very sharp scraper).

    I removed a fairly large surface area aluminium gooseneck fitting from an epoxy painted aluminium mast. It had been in place more than 25 years. The bolts came out fine but I had to carefully wedge the fitting away from the mast cutting away at the sealant with a fine blade as I went. Amazingly, at the centre the sealant had not fully cured after all that time. I reckon the bolts probably weren’t needed.

    Great stuff!!

    • John Aug 9, 2016, 7:21 am

      Hi Pat,

      If you can use that much polyurethane sealant without making a mess, you must have special powers. I bow to you.

      Still and all, I can’t see the benefit of using a very high adhesion compound on fittings (like that gooseneck) that may need removing at some point.

      One other thing, I don’t recommend trying to clean up 5200 with a blade once it’s dry. It’s extraordinarily hard to cut, even with a razor sharp knife.

      • Marc Dacey Aug 9, 2016, 12:19 pm

        John, I wore out 11 blades (!) on my sabre saw cutting through a bead of 5200 that a previous, delusional owner had used to seal my aluminum pilothouse roof from my mild steel pilothouse framing. It took me ages. It didn’t even accomplish the basic goal of isolating dissimilar metals. We are talking about maybe 20 linear feet. So I have felt your pain.

      • pat synge Aug 9, 2016, 7:27 pm

        As I said, John, I haven’t used 3M’s 5200. It may be harder with less elasticity and be more difficult to remove.

        I’m not saying I haven’t ever made a mess – far from it! But I’ve learned how not to and it’s not that difficult if you prepare well and take care. As soon as I get any on the vinyl gloves I peel them off and put on a new pair (the contaminated ones can usually be used later for other jobs – especially if promptly blown the right way out)

        The advantage of fitting relatively high load fittings (like goosenecks) with adhesive is that loads are distributed over a larger area and not concentrated at the fastenings. I was impressed that the thread cut into the aluminium was clean and shiny after 25+ years.

        • John Aug 10, 2016, 7:45 am

          Hi Pat,

          Hum, I don’t think that using a high adhesion bedding compound will actually make much difference to the ultimate fail strength of the bond or distribute the load, that is unless the adhesive in question is actually stronger than the bolts.

          The reason is the bedding compound has a much lower modulus than the bolts. As I understand it from the engineers around here, when two or more ways of attaching something are combined that have different modulus, the one with the higher modulus (the bolts) will take almost all the load. If that one fails, the lower modulus (the 5200) will then load up and fail. There will be no load sharing.

          Matt Marsh has a good article that explains this:

          And as far as keeping the bolt to aluminum bond interface in good shape, I prefer Tef-Gel:

  • Taras Aug 9, 2016, 5:07 am

    How about Sikaflex? I heard very good recommendations about it.
    And what do you recommend using for bedding thru hulls in aluminum hull?

    • John Aug 9, 2016, 7:12 am

      Hi Taras,

      I have always used the above mentioned Life-Calk for bedding through hulls in aluminium and never had a problem.

    • Drew Frye Aug 9, 2016, 8:30 pm

      Sika makes at least 30 products. I assume you are asking about Sika 291. Good stuff, not as tenacious as 5200, but still really strong if you have to take it apart.

  • John Aug 9, 2016, 7:16 am

    Hi Dick and Chris,

    Although I have not used it myself. I too have heard good things about butyl rubber from two marine technicians I respect who swear by it. Not sure I would use it under the waterline though.

  • Bruce Senay Aug 9, 2016, 10:39 am

    Goo Gone or Goof Off are great for getting 5200 off skin (don’t know about hair) as long as do it in 15-30 minutes. Admiral never believes me whenI am working with caulks that I try as hard as humanly possible but stuff has magical ways to appear even places I have not been near. Love your posts.
    s/v DreamCatcher
    Chiapas, Mexico

  • David Aug 9, 2016, 11:27 am

    We’ve used all the caulks and goos for one thing or another, learning some hard lessons along the way. Agree with you about 5200. We use it only for things where we want a strong permanent vibration-proof glue, not caring about it being water tight, usually inside the boat, and for NOTHING else. I think the problem is that it doesn’t have enough flex, so it looses adhesion in spots where things move, which is always somewhere.

    For mounting deck fittings, we now use either 3M UV4000 or butyl tape, depending on whether or not we want adhesion or just water seal. The UV4000 has less adhesion than 5200, although still a lot, but is more flexible to handle the flexing of surface and fitting. We haven’t had the same problems with UV4000 as with 5200. The main issue with UV4000 is working time, as it’s faster-setting, so you only have about 5-10 minutes of working time before it stops smearing smooothly, which isn’t enough for some needs-lots-of-smearing jobs.

    Butyl tape is amazing for keeping a seal for 20 years or more, handling all sorts of flexing and movement, but has very little adhesion and makes the mounting process harder as re-tightening is necessary over the first few days. We’ve even had success just glomming a little bead of it on around the edges of a leaking fitting to seal it before I have time to re-bed it, ending up leaving it there for years because it was working fine.

    We like your LifeCaulk also, for low-adhesion situations where butyl tape isn’t practical (need more goo-like consistency), and all sorts of internal mounting where we want it to be moisture proof and the caulk keeps things from vibrating loose when mounted in wood or fiberglass, like a mild Locktight.

    Sikaflex is our go-to for sealing teak decking pieces and any hardware we need to mount on an external wood surface (god help us). We also use Sikaflex in a bead for joints between interior cabinetry where there is a little movement.

    Be very careful about using silicon caulk for anything, as “silicon contamination” means that if the seal doesn’t hold and you need something stronger, you are out of luck. Nothing will ever stick to that surface again. No chemical will remove it. The only option is to sand the surface off to get to fresh substrate. Nightmare.

    For sealing frustrating little leaks in all sort of places, we’ve had good luck with Creeping Crack Cure, which is a very watery sealant that can flow along tiny cracks, even uphill, using capillary action. 3-4 applications over a few days will often solve the problem as it flows into the same crazy pathways that water finds its way through, eventually sealing them. It has often helped us delay a re-bedding for years, and made permanent fixes for other things.

    One of the most important things we’ve learned about mounting deck hardware with any of the caulks or goos (except butyl) is to ignore the advice you see around about lightly tightening initially, then fully tightening after the caulk has had time to “form a gasket”. Bad idea. All that does is ensure that you break the seal on the freshly made bond down the length of the bolt or screw, forming a nice pathway for a leak, and a perfect place for oxygen starvation crevice corrosion in stainless. Even if you try to hold the bolt still and just turn the nut, you usually end up accidentally turning the bolt a little too, creating a future leak. Tighten that sucker right off the bat and leave the seal intact. Then don’t touch it until it’s time to re-bed it many years later. Butyl is the exception. It “flows” very slowly into the joint, over a period of hours or days, so it seeds to be tightened repeatedly until the nut doesn’t seem to get easier to move after each wait. Try to turn just the nut and not to turn the bolt. Yes that’s hard. Swearing helps, unless your wife is helping, in which case you may end up with goo in your hair and a wrench where it’s painful to remove.

    All this talk of leaks and goo is making me wish I had an aluminum boat like yours with most deck hardware welded on and a hundred fewer places to leak. Well played Sir.

    50′ cat

    • John Aug 10, 2016, 7:50 am

      Hi David,

      Lots of great tips, thank you. Particularly good point about the dangers of using silicon based products.

      And I agree that the idea of tightening a fitting after the bedding sets in flawed. I have always tightened stuff down immediately with Life-Caulk and never had a problem.

  • Paul McEvoy Aug 9, 2016, 12:21 pm

    Butyl tape as described above seems like a no brainier at this point. Zero mess.

  • Klaus@Starship Aug 9, 2016, 1:00 pm

    And how about 3M’s 4200? Just bought my first one an hour ago.
    I so far used Sikaflex (eg 290i), but only got 4200 here in Tenerife this afternoon.
    Any comments on 4200?
    Best, Klaus

  • Bill Wakefield Aug 9, 2016, 4:01 pm

    Hi John,

    You are preaching to the choir here… If something like 5200 is needed, I have defaulted to 3M UV4200 with success.

    However, for routine bedding tasks, I switched to the butyl rubber [tape] camp years ago. As Dick already mentioned, you need a good formulation, and you cannot usually find that at an RV store… [I use the same source Dick referenced, above…]

    I am also a long time user of Dolphinite. It is like butyl rubber in that is has low adhesive properties, but excellent, enduring cohesive properties. I use Dolphinite where butyl rubber tape is not convenient. [e.g. larger surface areas, places that need re-bedding often due to routine inspections (e.g., chain plate covers) etc.] Like butyl tape, Dolphinite lasts seemingly forever in place- and it its can…

    I haven’t used 5200 in 25+ years, but I’m pretty sure there is still some stuck to my scalp somewhere…

    Great article and caution for the uninitiated…

    Cheers! Bill

    • Drew Frye Aug 9, 2016, 8:46 pm

      You mean 3M 4000 UV (there is no 4200 UV).

      BTW, 4000 UV is polyether and is not really related to 5200 and 4200. Which is good, because it is better.

      • Bill Wakefield Aug 9, 2016, 8:59 pm

        Thank you for the clarification, Drew.

        That is what I get for trusting my memory… It has been a few years since I have used any…

        I do remember the UV, so it must be 4000 UV as you said. I also remember the results were noteworthy, and it was a tad easier to work with than 5200.

        Cheers! Bill

  • Kevin Ladenheim Aug 9, 2016, 6:22 pm

    If you do have to work with 5200, 3M recommends 38984 Specialty Adhesive Remover as the solvent for surface prep and cleanup. It just instantly dissolves the stuff, you can even use it to tool a nice bead. It’s very expensive at about $35/quart and the MSDS is pretty scary but it works.

  • Drew Frye Aug 9, 2016, 8:44 pm

    I’m finishing up a bunch of testing for Practical Sailor as we speak. A few thoughts:

    I’m a butyl fan, where it works. I love it for hatches, because of the ease of removal. I use it anywhere I don’t feel I need an adhesive.

    3M 5200. Very strong… BUT the adhesion to aluminum and all plastic is hit or miss. It can be strong, or it can peel at very low force. I’ve seen this on my boat over the years, and it was clear in testing. The ONLY thing I would use it for is permanent FRP-to-FRP bonding, like a deck/hull joint. It is also much less flexible than sealants. Also, 3M 4200 suffered from the same hit-or-miss adhesion.

    Sika and Locktite. Lots of great products with a wider range of adhesion. I like Sika 291 and Locktite Marine.

    I’ve not been impressed with Boatlife Caulk. I find it peels off too easily and leaks. Boatlife Seal does better.

    The bargain, without peer, is Locktite PL S40. A polyurethane much like Sika 291 or 3M 4200 (with better properties) but for only $5.85/10 oz. Try it. I’ve been using it for years and find it delivers top performance of 30% of the price. Flexible, with much better multi-surface adhesion than 3M 5200 or 4200.

    I also found a great remover to silicone (100% bond strength when followed with PU), but none of them really did anything for polyurethane or polyether.

    • John Aug 10, 2016, 7:35 am

      Hi Drew,

      Lots of good information, as always, thank you. Having said that, the more I think about it, the more doubtful I become about the benefits of high adhesion in bedding compounds—the success of butyl would seem to support that thought. The point being that although, as you say, Life-Caulk does not stick that well, I’m not sure that then making the leap that therefore it leaks, is correct. That has certainly not been my experience and I have been using it for some 30 years.

      Note that I’m not saying that Life-Caulk is the best, but rather that testing adhesion maybe a red herring, or even counterproductive, when we are thinking about bedding.

  • Westbrook Murphy Aug 10, 2016, 2:08 pm

    Anti-Bond worked wonderfully for me in removing 3M5000. Last I knew Anti-Bond still was available from West Marine.

    • John Aug 11, 2016, 8:06 am

      Hi Westbrook,

      Good to know that the stuff does work, although at the same time, a bit worrying. What size fitting were you removing?

      • Westbrook Murphy Aug 11, 2016, 12:58 pm

        Used Anti-Bond two different times:
        — On 2″ through hull cockpit drain that had begun to leak and rotted the fiberglass on the inside of the hull. Much grinding and then fairing Marine Tex on the inside of the hull. Then Anti-Bond to loosen the outside flange. Rebedded the flange with 5200, which leaked. Used Anti-Bond to loosen the bedding from the day before, rebedded a second time with 5200 and all was well. When the boat was at rest, the through hull was above the waterline, so repairs were made without hauling the boat.
        — Loosening a decorative teak frame around the hatch in the main cabin ceiling. 2″ wide frame for a square opening about 2′ on each side. Frame had to be removed to then remove the decorative ceiling of plywood sheets to which a vinyl sheet had been attached with glue that was giving out so than the vinyl was falling down. (That’s the end of the Anti-Bond portion of the story.) Set up a big table in my garage; used a solvent of some kind (not Anti-Bond) to finish disconnecting the vinyl from the plywood and remove the old glue from both surfaces; then reattached the vinyl sheet to the plywood with a spray glue I ordered from 3M (don’t remember the name); and then reinstalled the ceiling panels in the boat. I reused the old sheet of vinyl, which required lining up the edges and hole for the hatch while gluing it to the plywood. Were I to do the job again, I’d buy a new sheet of vinyl, glue it down, and then trim the edges and cut a hole for the hatch. Did NOT use 5200 when reinstalling the teak frame around the hatch.

        • John Aug 12, 2016, 8:20 am

          Hi Westbrook,

          Thanks, that confirms that Anti-Bond actually works on a fitting. All the videos on their site just showed a lump being loosened, which is not the real world.

          Of course that still leaves the question, if a water based product can dissolve the stuff so easily…

  • Henning Aug 10, 2016, 7:19 pm

    5 years ago I have installed numerous new deck hardware on my balsa cored GRP deck and used a polyurethane-based sealant + adhesive called Pantera which is made in northern Germany and strongly favored by the yards here. It is not nearly as strong as 5200 but I have pulled off the gelcoat with it, too, on one occasion. Later I was told to use a heat gun on any smallish metal fitting. The goo will give up eventually and the gelcoat will not be marred badly if the heat is applied to the metal only. However, I don’t know how well that’s going to work on a hatch, for example.
    That was before I read Rod Collins article on butyl tape (linked to above). Now I would use butyl tape and have a roll in the bilge already. On a heavily loaded fitting like a genoa car track, I can feel the impulse to use a strong adhesive myself but I will resist it in the future. It really needs to be bolted on immensely strong and then all that is needed is a seal and butyl is perfect for that. A longish aluminum track, for example, will always expand and contract with temperature differently than the GRP deck so any goo that hardens completely must fail eventually, even if it ends up pulling loose pieces of gelcoat.
    On all of the holes in the cored deck I have drilled out the balsa around the hole ideally 1 inch wide, at least 1/2 inch with a nail with its head cut off and bent 90° in a handheld drill. Then I taped the bottom hole closed and filled he whole thing with epoxy from a syringe and, after curing, drilled a new hole. The collar from epoxy around the hole that results will seal the core against moisture but primarily it will take the compression load from the bolt. For the Genoa tracks I then used strong and large metal plates on the underside, screwed and epoxied to the laminate from below. When I tightened the 1/4” bolts on the tracks I could feel that there was no compression at all and that I could have easily snapped off all the bolts had I wanted to.
    I think that this makes life much easier for the sealing compound and obviates any need for an adhesive. After 5 years, all the 60 or so holes I put in my deck in this way are still tight.
    But I, too, am dreaming of an aluminum deck with everything welded on.

    • John Aug 11, 2016, 8:04 am

      Hi Henning,

      Thanks for the really good description of how to properly attach a track on a cored deck. We used exactly the same process on our old fibreglass boat and has similar good results.

  • Neil McCubbin Aug 11, 2016, 3:24 am

    Interesting stuff on the butyl rubber tape. I will buy some for future use
    Concerning the goop option, we have had great results with the more flexible Sikaflexes, particularly 291
    One trick to minimise mess is to bolt the fitting in place, rub on a coat of vaseline all around the joint, take the fitting off, apply plenty goop, bolt it finally then come back next day and trim the excess easily with a knife. Teh goop stays in the joint, but does not stick to the grease.
    The vaseline is much less work than masking tape, particularly in complex shapes, and is more effective because the goop does not get under it. Scrub the vaseline off with soap and water when the goop is cured.
    When we want to able to remove an item, we put a thin coat of Vaseline on one side before bolting up.

    • John Aug 11, 2016, 8:02 am

      Hi Neil,

      Great tip, thanks.

  • Bill Attwood Aug 11, 2016, 7:14 am

    To add my 2 pennyworth:
    At the start of my refit I used PU bedding/sealant. Unfortunately, one of the new deck hatches had to be removed a year later, and that convinced me never to use the stuff again. The reasons have been well covered above. Equally unfortunately the other new hatches and new windows were all installed using PU, so I hope they won´t require removal in my lifetime.
    I have become a complete convert to Butyl rubber, and now use it in all cases where just bedding is required, ie where mechanical fixings are there. The only complaint I have is that when the butyl is squeezed out as the screws/bolts are tightened, it looks a bit ugly, and is difficult, but not impossible to remove. Polypropyl alcohol was recommended as being useful for this, but didn´t work for me. As regards adhesion, I find it excellent. I had to remove a couple of other fittings bedded with butyl (no wonder this refit is taking so long) and it needed wedges to get them started. Then as the fitting came away, there were long strands of butyl stretched out between fitting and deck, but no damage to varnished teak or gelcoat. Removing the remaining butyl was done by just rolling it up with my thumb. The key difference I believe, is that butyl rubber sticks well to most everything, but best of all to itself. Another success story for me has been the use of MS-Polymer adhesive to stick small wood bearing blocks, eg for carrying cable channel brackets to the inside of a grp hull. The construction adhesive available in building suppliy markets is cheaper than the equivalent in chandlers, and it works really well, with a firm initial tack, meaning the block doesn´t need to be braced or taped in place. As a test I first fixed and then removed one of these blocks, which confirmed the excellent holding power of MS-Polymer
    Yours aye,

  • Dave Aug 11, 2016, 7:23 pm


    In the past 40 years I have tried most the products available. About 10 years ago I settled on making custom gaskets out of hard thin weatherproof rubber sheet material. The rubber sheet is glued to the bottom of the fitting and then trimmed. I then use a small amount of dolphanite as a belt and suspenders approach. Never seal the underneath side of the hardware below deck. Most boats do not have the core sealed around the hardware penetrations. The rubber seems to allow for any movement between dissimilar materials with temperature changes. This method looks good, allows for easy removal and has worked better than any sealant I have previously used.

    • John Aug 12, 2016, 8:22 am

      Hi Dave,

      I too have done the same in a couple of places where I know I will have to remove the fitting in question, and it has always worked well. Maybe I can use the technique more widely. Thanks

  • John Aug 12, 2016, 8:26 am

    Hi All,

    Wow, what a great body of knowledge and experience you AAC readers have! Collectively you have taken a simple post and turned it into a manual on effective fitting bedding techniques. Thanks very much.

    Any more great ideas on bedding fittings out there?

    • Dick Stevenson Aug 14, 2016, 1:03 pm

      Hi John,
      No more great ideas for bedding, but as always, the fine tuning is in the details. For details I mean suggestions such as chamfering the holes (in a fg boat) for a securing bolt to allow there to be more effective bedding around the bolt where it enters the deck. That and other such details can be had at the aforementioned web site of Compass Marine, It also has a wealth of knowledge and suggestions in the use of butyl rubber as a bedding compound (as well as other marine projects).
      My best, Dick Stevenson, s/v Alchemy

      • John Aug 14, 2016, 4:14 pm

        Hi Dick,

        Another really good tip on chamfering the holes, thanks. That in conjunction with butyl rubber is going to make a sort of “O” ring isn’t it, Gotta be good.

        I also agree about Compass marine. Great stuff and highly recommended. In fact I just made a $20.00 donation to his site. I urge others to do the same.

        • Dick Stevenson Aug 15, 2016, 9:15 pm

          Hi John,
          I am so glad you mentioned supporting Compass Marine web site with a $$ contribution. It felt presumptuous for me to do so on your site, but I certainly thought about it and was heartily glad you did so. I support it with contributions and also urge others to contribute.
          Thanks, Dick

  • John Aug 12, 2016, 8:32 am

    Hi All, again,

    Added to my comment above, for me the big takeaway from all of this is that adhesion is not what counts in making a long lived waterproof seal between the a fitting and a boat, and in fact really strong adhesion might be detrimental.

    • Dave Aug 12, 2016, 9:16 am


      Exactly the right conclusion. The movement of dissimilar materials is impossible to stop. The greater the changes in temperature, the greater the movement. Why not engineer for that movement. I have also used O rings of various sizes with great success.

  • David Howes Aug 12, 2016, 2:06 pm

    On our crossing this summer we had several troublesome deck leaks, primarily through the bases of our bulwark mounted stanchions which had been professionally mounted using 4200 the year before.
    A shipwright in Horta gave us a chunk of thin, adhesive-backed, neoprene. He instructed us to apply the adhesive to the metal , not the gelcoat side, punch the bolts through, and bolt tightly. Trim around the fitting with a utility knife.
    Long story short, the neoprene worked beautifully. It is too early to know how long the repair will last, but he testified that he has found it to last for many years.

    • John Aug 13, 2016, 7:50 am

      Hi David,

      Now that’s interesting. I amazed that it does not leak around the bolt holes, but the proof is in the testing. Thanks.

  • Alan S Aug 13, 2016, 7:41 pm

    Re Sika 291, we have found in high UV locations such as NZ the exposed edge turns yellow quite quickly. Similar to others I have found 3M 4000 good to use, and it certainly has quite a tenacious bond, but comes off reasonably easily if you can get a thin wedge under one edge of the fitting. Alot of the boatbuilders here are favoring the MS Polymer products.
    I might add I have found when removing old fittings sealed with silicon sealants, that some virtually fell off whilst others were stuck as tenaciously as a 5200 bond.
    As an alternative to a heat gun, copious quantities of boiling wáter on a metallic fitting can be enough to soften the sealant sufficiently to break the bond

    • John Aug 14, 2016, 10:04 am

      Hi Alan,

      Great tip on the boiling water, thanks. I’m always nervous about using heat guns around fibreglass since I believe I’m right in saying that excessive heat can weaken the laminate and it’s hard to know exactly how much you are applying.

  • Dick Stevenson Aug 14, 2016, 1:07 pm

    Boiling water is a big help for a variety of challenging chores. Making a pad of absorbent cloth can concentrate the heat when water is poured over it, whether a deck fitting, but also over hose to barb fittings that are giving trouble. The water/heat then stays more in place and is less of a mess. m
    Dick Stevenson, s/v Alchemy

    • John Aug 14, 2016, 4:15 pm

      Hi Dick,

      Another good one, thanks.

  • Dave Aug 15, 2016, 9:09 am


    A typical use for a O ring would be hand rails fastened from below deck. Cut a recess in the center of the bottom of the rail where it meets the deck. Fill the recess with dolphanite. Use the proper size O ring over the screws, between the deck and hand rail. Bolts with sholders also will seal very well. The key is to choose the proper application and size O ring.

  • JCFlander Aug 27, 2016, 3:11 pm

    Regarding that intolerable mess – we have got excellent results on removing Sika 291 stains with a product called CRC Bräkleen. It removes stains completely and doesn’t seem to attack gelcoat.
    That product is meant for cleaning brake pads and other brake components, not sure about it’s constitution but effective component is likely methyl- and cyclohexane. Not excessively toxic.

    There’s other product that works to PU is called SurfaSolve – that is used on boatyards instead of acetone, and that works also on Sika 291 stains very well. It’s not toxic at all. Very good stuff.

    I believe 3M 5200 is quite similar to Sika 291, so those two products could work to that and come handy in “damage control”.

    Cheers, Petri

    • John Aug 27, 2016, 5:43 pm

      Hi Petri,

      Sound like good tips, thanks.

  • Steven D'Antonio Sep 1, 2016, 8:10 am

    After nearly 30 years in the marine trades, my strong suspicion is that many, if not most, bedding failures are the result of lack of or poor surface preparation. I decided to tackle this challenge while running a boat. Try this experiment, using a clean white rag, soak it in mineral spirits, and then wipe down the hardware you intend to bed, hatch frame, port, cleat, fasteners etc. The rag will almost certainly come away black with cutting oil, and polishing wax residue. In the boat building world we use wax to prevent things from sticking together, like fiberglass parts and the molds in which they are built. It’s problematic when bedding to say the least, and leads, I believe to leaks. Very few pro’s I work with religiously de-wax hardware and bedding surfaces before installation. This is a prerequisite, the hardware, fasteners and surface to which they will be bedded must be de-waxed, and the rag used to do this must be free of contaminants, including detergent and surfactants.

    With John’s permission I’ll post a link to an article I wrote on proper bedding technique, surface prep etc.

    I to am no fan of 5200 (who is?), and lament the day 3M stopped manufacturing 101, their polysulfide product (I husband a small supply in my shop refrigerator). Lifecaulk is an alternative which I now use. Polyurethane and polysulfide should not be used on most plastics, by the way, silicone, with all its caveats, is preferred here, I use GE Silpruf.

    I can attest to the adhesive power of 5200, I’ve lifted boats off the ground in a travel lift, unscrewed all the keel bolt nuts and the keel remained attached solely as a result of the 5200 bedding between it and the keel stub.

    • John Sep 1, 2016, 9:21 am

      Hi Steve,

      Good point on proper cleaning. I know I have made that mistake.

      Any yes, please post a link to your article, I know we will all learn useful stuff.

  • Steven D'Antonio Sep 1, 2016, 8:14 am

    One further thought on bedding/sealant, I have struggled to find one that, when used as an exposed fillet, will not mildew in the tropics. If anyone has a sure fire product/solution, please do share.

    • Dick Stevenson Sep 1, 2016, 5:03 pm

      Hi Steve,
      Not sure fire as yet, but the butyl rubber has gone 3 years in the Med and 5+ years in Northern Europe with no signs of mildew/mold. It is actually in Northern Europe where things have turned green most quickly, especially after a winter of sitting about. The BR has shown no signs of mildew while other objects have taken on the distinct hue of mold/mildew. I will keep a closer eye on the BR and report back in the future.
      My best, Dick Stevenson, s/v Alchemy

  • Steven D'Antonio Sep 1, 2016, 9:32 am

    Thanks John, here’s the link.

    The subject of the article is on cored composite construction, with a sub-section on sealant, bedding and surface prep.

  • Richard Hudson Sep 26, 2016, 9:37 pm

    Very informative post, especially in the comments.

    I try to have a few cartridges of polyurethane adhesive sealants like 5200 (I buy whatever is available wherever I am) aboard. Among other uses, I find them excellent for sail repair. I use the polyurethane adhesive sealant to glue a patch of sailcloth across a tear in a sail, with a few hand stitches around the patch to hold it in place until the glue dries.

    I have had better results with sails patched with polyurethane adhesive sealants than with sticky-back polyester patches. I think the reason for this is both that the sealant is fluid enough to get right into the weave of the cloth, greatly increasing contact surface area, and that my surface preparation, when repairing while on passage (which is when the sails typically rip, so when I want to repair them), is not as good as it would be in a sail loft–particularly it is often difficult to get the cloth really dry when at sea.

    • John Sep 27, 2016, 6:17 pm

      Hi Richard,

      I agree that emergency sail repair is a good use for 5200, one of the few in my opinion. For this use, I have found the quick dry version the best option. One caveat though, if one then takes the sail repaired with 5200 to a sailmaker for permeant repair, the invoice is likely to be a lot bigger than it would be had sticky back cloth and a bit of stitching been used in the temp repair.

      • Richard Hudson Sep 27, 2016, 9:36 pm

        Hi John,

        Good point that if one were to take the 5200-repaired sail to a sailmaker to redo the patch it would be much more labor and expense.

        I’ve never considered the sail repairs that I’ve done with the 5200 and similar to be anything but permanent. As long as the patch is big enough to get a good amount of contact area, and it had time to dry before any flogging or big loads happened, I think the blessing & curse of 5200’s great adhesion means that the patch will not come apart.

        Aesthetically, as long as one was able to buy white 5200, I think a white patch of sailcloth on a white sail looks fine. My multi-colored spinnaker, on the other hand, with many 5200 repairs made using whatever pieces of nylon I had aboard, looks very “well-traveled” or “beat to hell” depending on one’s point of view :).


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