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I have a more than 50 years old folding kayak (Klepper) the frame of which is made out of Mountain Ash and Baltic Birch.

There is a large crack in one of the bottom parts of the boat on top of which the seats are placed. This part is also submitted to an important pressure during the assembly of the boat.

top view cracked wood

close up view cracked wood

I would like to know what are the best strategies to fix this crack and prevent it from completely breaking. If possible, one that does not require too many specialized tools.

Would glue be an option (which type)? wire? webbing? or a combination of those?

Thank you!

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    One important note in relation to the suggestions in the Answer you've received so far is that if this is finished in varnish — and there's every expectation that it is finished in as spar or marine varnish — I would caution against using acetone to clean up the excess wet or just-starting-to-cure epoxy. In other circumstances acetone would absolutely be my no. 1 choice (because it's most effective of the common solvents) but working on a piece that is already finished is one of the few times where you don't want to resort to it, because it's also damaging to many (most) cured finishes [contd]
    – Graphus
    Sep 3, 2022 at 18:11
  • This doesn't mean you can't use it, but be aware it is likely to damage the surface (at the least dulling it down or worse make a streaky mess, depending on how fast you can work. This can be fixed relatively easily, but you probably want to avoid having to, so I would go with choice no. 2 and that's an alcohol. Ethanol is too hard to find, so go with either denatured alcohol (probably available in every hardware store and big-box) or isopropyl, which I think you'll find in the pharmacy aisle in any Walmart, or failing that CVS/Walgreens. You want the 91% if you can get it, and not the 70%.
    – Graphus
    Sep 3, 2022 at 18:18
  • Thank you @Graphus for the precision. This is correct, there is a varnish. I'll go for ethanol , which I have access to since I work in a lab!
    – michltm
    Sep 5, 2022 at 16:37
  • Ah lucky you! If you ever get into woodworking enough to want to use shellac, ethanol is THE solvent for dissolving shellac flakes or diluting liquid shellac, if one can get it.
    – Graphus
    Sep 7, 2022 at 18:56

1 Answer 1

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If the break is the result of too much force, and not due to decay in the wood, it can probably be very adequately repaired. To do this you need: a thin bladed tool such as a narrow putty knife (in fact a couple, of varying widths might be good); several clamps that will fit in the space you have to work, but provide good clamping pressure; a good epoxy with a relatively long working time - at least 20 minutes or more; packing tape; acetone or ethanol (for cleanup); a couple of shop rags.

First, you want to work the crack open a bit more with the knives. You want a crack into which you can confidently work a thin epoxy as fully as possible, but you also want to be careful not to fully break the original wood, so work carefully. Then tape the bottom of the crack (to prevent the epoxy from all running out) with the packing tape. Now in a warm place, with everything warm (minimum 25C), mix the epoxy. You want a relatively thin, flowable mix, so the warmth is important. Don't be afraid to warm the resin and hardener in a hot water bath before mixing if neccessary to get this. A throwaway trial mix is worth the time, if you have doubts. Work the epoxy into the crack by dripping it in, and working with the knives, until you're confident you've got the crack filled as thoroughly as possible. Clamp the piece to bring the crack together well - doesn't have to be super tight, but the crack should be closed, and epoxy should squeeze out all along the crack. Wipe away excess epoxy on the outside after clamping, then wait until the remaining residue has become quite tacky, and use the acetone or ethanol to clean that off the piece. Leave the clamps on for 24 hours.

If you work carefully, you should end up with an almost invisible repair that is a strong or stronger than the original wood.

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    I can't remember how Klepper parts are attached, but I'd encourage you to separate this part from the rest of the frame to work on it, if you can. Sep 3, 2022 at 19:58
  • Thank you for this very detailed protocol. I can confirm that the break is only the result of to much force. I will follow the protocol and come back with some updates of the result after trying the kayak. Yes, the part can be separated from the rest of the frame.
    – michltm
    Sep 5, 2022 at 16:34

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