Resealing bulkhead

Discussion in 'General Paddling Discussions' started by pawsplus, Nov 6, 2015.

  1. pawsplus

    pawsplus Paddler

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    So my stern bulkhead leaks. :( Found this out when we were doing rescue practice and the cockpit filled with water repeatedly--when I went to load the boat I found that the stern compartment had water in it. Filled the cockpit as a test to make sure it wasn't the hatch cover, and it's not.

    So . . . it's a WS Tsunami 140, less than 2 years old. It's not silicone used to seal the foam bulkhead in place--what is the name of the other stuff? Do I just run a bead around it on both sides and let it dry?
     
  2. red kite

    red kite Paddler

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    You are looking for Lexel, usually found in the sealant section of a good hardware store.

    To make a long lasting seal there is more to it than "just running a bead around it". But even if you do the later:

    Take all the old sealant off, roughen the section on the boat where the Lexel has to stick and wipe it with rubbing alcohol. Apply sealant.
    This probably lasts you several years longer than the factory seal but might need redoing down the line (the temperature differences between summer and winter in your area likely don't help.)

    Hint: Never use acetone on a poly boat, it's going to be really really messy really fast. :yikes:
     
  3. pawsplus

    pawsplus Paddler

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    I thought only with silicone did you have to totally remove the old stuff?
     
  4. red kite

    red kite Paddler

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    Well, I personally always take the old stuff off when resealing something - there is a reason that the old stuff failed, and old parts can compromise adhesion of the new stuff.

    But it's your boat, you don't have to take my word for it.

    Good luck! :big_thumb
     
  5. pawsplus

    pawsplus Paddler

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  6. fishboat

    fishboat Paddler

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    A pic of the leaking spot might help.

    If there is loose sealant in the area it would be good to remove it (and only the loose portion..gently slice it out with a razor if need be) as it isn't sticking to anything. Laying new sealant on top of a loose piece won't get you where you want to go.

    Lexel might be your best bet.

    Wash it with soapy water and rinse, as the wilderness site indicates. Roughing the area up a little with 60-80 grit sandpaper wouldn't hurt as it'll give the new sealant more bite. After you wash/rinse the area and let it dry, douse the area with rubbing alcohol or denatured ethanol(better, as rubbing alcohol has ~ 30% added water) and let it dry some more. It looks like pharmacies carry 91% pure alcohol in addition to the 70% pure..use the 91%. This is a key point that most often isn't mentioned. Anytime you wash something like this with water, the water can get trapped in small places, like the seam you're trying to seal, and can take very long to dry out. That water can keep new sealant from adhering as it needs to. Dousing the area with alcohol(pour it on and wipe it dry with a paper towel..let it air dry more) serves as a drying aid as it dilutes the water with a medium (alcohol) that dries MUCH more readily & thoroughly. This is a standard drying technique that's used in chemistry labs after washing glassware. As you're laying the new bead, try to fill the dip in the keel (where you mention it's leaking) and then smooth the bead over the top.
     
  7. pawsplus

    pawsplus Paddler

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    Thanks!
     
  8. Astoriadave

    Astoriadave Paddler

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    I like fishboat's procedure. The solvent is often sold as denatured alcohol. A pint is enough to last a long time. Oh, right ... you are an alcohol stove maven. You know all this stuff already.
     
  9. gifind

    gifind New Member

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  10. davidcarlsson

    davidcarlsson New Member

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    I can also recommend 3M 5200 or Sikkaflex 291 fast cure. Of the two, I prefer Sikkaflex as it is a little more viscous. Both should be available at most boat supply or Chandlery's. I remove any loose sealant, then use 90% Isopropyl Alcohol to clean everything on rotomolded boats prior to laying down new sealant.
     
  11. JKA

    JKA Paddler

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    Necro post, but a similar question.

    I'm moving the foam bulkhead in my poly Chatham 16, and I've lost the instructions given to me by a kayak manufacturer on how he seals his.

    I remember that it involved flaming the plastic and then applying contact adhesive which was allowed to set, before gluing the new bulkhead in with Sikaflex-291.

    Does this sound familiar to anything anyone here has done, or are there other suggestions? I note that I'm in New Zealand, and some of the adhesive/sealants that are common to you are not easily available here.

    I've moved them before, but I want to hear what others have done, as there's often better ways of doing things that seem simple.

    Cheers

    John
     
  12. mick_allen

    mick_allen Paddler & Moderator

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    As a starter, this is an interesting 3M paper that discusses surface energy and adhesion with respect to different materials and surface treatments.

    https://multimedia.3m.com/mws/media...bonding-to-low-surface-energy-white-paper.pdf

    some outtakes from that paper:
    Adhesion3M-a.jpg

    Adhesion3M-b.jpg

    So, if you do not have availability of either related ‘adhesion primers’ or related ‘Plastic Adhesives’ that can bond to LSE [low surface energy plastics] then the heat treatment approach would be the one to take.

    If it was me, I’d err on the side of not melting the kayak, but heat treating seems fairly easy. As it will be from the inside, I’d make sure that there was good stable setup and then I’d rehearse the moves a little bit. With an open hot flame like this, it’s helpful to have various safe placement scenarios worked out – ie don’t lay the lit torch on it’s side inside the yak while it all rolls around, heh heh!
     
    Last edited: Oct 8, 2018
  13. Astoriadave

    Astoriadave Paddler

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    Good advice, Mick. Flame treating poly surfaces is a delicate endeavour. Get a spreader on the tip of the torch. Better to treat widely than on a pin point. The usual torch off the shelf is far too focused. And, avoid yellow or smoky flames. They can deposit hydrocarbons snd soot.

    Finally, TEST and PRACTICE on scraps of polyethylene. Yaks have thin skins, and overheating melts holes easily.
     
  14. mick_allen

    mick_allen Paddler & Moderator

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    Dave, so on my cheapish butane [I think ] torch, the outer part of the flame is yellowish and the inner close to the nozzle is the bluish colour: so the tip should be held [moved, say] close to the surface?
     
  15. JKA

    JKA Paddler

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    Thanks Mick,

    While I don't understand the science behind this, would the contact glue that was put on after flaming be a "solvent based adhesion promoters that contain higher surface energy resins which entangle with the low surface energy substrate when the solvent swells the surface"?

    Re the flaming, does the process of heating the plastic have a lasting effect, or does the material's surface energy return to status quo on cooling? In other words, do I have to move fast after flaming?

    Also, I have seen foam bulkheads that are smaller than the internal size of the kayak, and a 'foundation' piece of thinner foam is glued on first. This piece is wider than the bulkhead, which effectively gives a bigger footprint. The bulkhead is then glued to that. Does this explanation make sense? If so, can you see an advantage in doing this?

    Cheers

    John
     
  16. mick_allen

    mick_allen Paddler & Moderator

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    Dave is the king of materials, so wait until he responds further. . . My understanding is that the flaming treatment effectiveness deteriorates fairly rapidly so probably it is best to proceed to adherence within 10-15 minutes of flaming.

    And reading the pdf mentioned, the flaming is an alternative to using an adhesion promoter. So if using effective flaming, contact gluing would happen next - no promoter necessary.

    As far as wide foam bulkhead bases being effective for thinner bulkheads, I wonder if this is more of a structural issue with respect to the thinner bulkhead resisting the strong forces of water in a flooded cockpit. I do not have experience with situations where this might be an issue [with foam, that is - heh heh], but I could imagine it. In other words, if we assume that all parts of a foam bulkhead were glued in securely [which is the natural first assumption], logically to me, size for size, a bulkhead that had a wider and fairly thick perimeter base would be more able to resist water impact forces than one that had no wide thick base. This is size for size. Like a retaining wall with a foundation is more resistant than one of the same height that has no foundation [assuming they are rigidly connected!].

    But I'm guessing - and those who have direct knowledge of what you're talking about could chime it if desired.
     
  17. rider

    rider Paddler

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    I would use a razorblade to cut off any loose adhesive, 40 grit paper to rough up the hull where the new stuff is to be applied, clean up the area with methyl hydrate on a rag and apply new sealant, probably Marine Goop. If the boat is only 2 years old, sounds like we're dealing with localized separation and not a wholesale adhesive failure, so I would not make it into a make-work-project by trying to remove the "old" stuff.
     
  18. Astoriadave

    Astoriadave Paddler

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    I parsed that 3M pdf as well as I could, and I think my crown is askew, or very tarnished at the minimum. In this context, I am not sure what "high surface energy" means, at all. I believe it is a term from a thermodynamic approach to adhesion, which leaves me cold. And unflamed. Maybe inflamed or burnt, coldly.

    Bottom line seems to be that some (at least temporary) chemical changes are needed to permit any adhesive to grab onto the surface architecture. Flaming of hydrocarbon surfaces exposed to air should oxidize the hydrocarbons to aldehydes and ketones, which may only last a short time on the surface before they get rolled under, leaving the surface a sheet of hydrocarbons again. Any exposed aldehydes and ketones, especially the former, can then engage in chemical congress with adhesives seeking carbonyl groups to hook up with. That could be confirmed if condensation reactions with amines or amides in the adhesive promoted long term bonding, but there is no mention of that in the 3M article.

    Sorry.
     
  19. JKA

    JKA Paddler

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    Thanks for that Dave.

    Sadly, I have no idea what anything you said meant! :)o_O

    I pulled out the old foam bulkhead, and discovered that it had no sealant except for around the edges. Even then, they weren't chamfered so the sealant was basically not working as any kind of adhesive, it just tidied up the edge!

    My plan is to roughen the kayak's surface, flame it and afix the new foam bulkhead with Sikaflex 291. I'll chamfer the edges of the new bulkhead, as well as cut a groove into the edge around the circumference, which I'll fill with Sikaflex, hopefully to act like an O ring. Once it's in place I'll pump more Sikaflex into the edges, feathering it out to provide a wider footprint.

    Should be a messy little job, and by the time I'm finished I'll be skilled at removing Sikaflex from every surface.

    Cheers

    John
     
  20. mick_allen

    mick_allen Paddler & Moderator

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