Scarf failure.

Not the happiest moment when I glanced around the starboard side of the sharpie and found my freshly attached chine log split at it’s scarf.

I am not sure when it spit, but I know I let the joint bond over several weeks before bending it on the boat. I don’t think any one element caused the failure, but here are my suspicions in order of potential culpability:

  1. Did not wet out joint with thin epoxy before adding the thickened.
  2. The joint may have been clamped too tightly thus squeezing out too much epoxy.
  3. Mixing ratios of the e-glue may have been off, it is tricky to measure 50:50 when the A and B parts differ so greatly.
  4. Position of scarfe. Why oh why did I put the scarf at the place of greatest twist and tension!? The stern quarter really kicks up on an NIS.

Regardless of what actually happened, such failures fill you with doubt. I have had great success with traditionally thickened epoxy; whilst mixing it seems to take an age, you can be sure it is mixed. This e-glue worries me.

I have spent some time researching my worries about the e-glue, and I have yet to hear a concern from anyone, so I have relaxed and continued to use it but with attention to the ratio and wetting out of joints first.

About paulatkins

I own a 3rd generation family businss printing for lovers of photography. My favourite hobby is building and sailing wooden boats.
This entry was posted in Epoxy, wood work. Bookmark the permalink.

4 Responses to Scarf failure.

  1. Phillipe says:

    Hi Paul

    Do you have any pics of the actual failed joint up close?
    Did the glue line crack?
    Did it pull timber from the surface of the scarphs?

    Questions questions questions 😎

    I did have one failure on my NIS18 when I glued in my inner keelson to the bulk-heads. The glue actually cracked. These were my first ever joints done with e-glue, so failure to thoroughly mix and/or not allowing to fully cure, as well as not insignificant shrinkage of the oregon keelson due to reduction of moisture content may have contributed (timber was pretty ‘wet’ or ‘green’ when I fitted it). Since then, we have had no cracking in any E-Glued joints (lots of them over the past 18 months), so I am very confident in the product. We have also made sure joints are compound where ever possible (i.e. not just a single face – include a 90degree face where possible). I think the various forces in your joint would have played a significant part in the failure – there would have been a combination of signficant sheer, tension and twisting forces at play, acting on a single joint in one plane. Lots of variables, but is sounds like you have worked it out so you get good joints now.

    Cheers

    Phillipe

    • paulatkins says:

      Hi Phillipe,

      Thanks for your analysis. I didn’t make a better photograph of the joint. Ashamed I suppose!

      The glue definetly gave way as each half had fine glue “balls” on the surface, like if you pulled apart a wet joint, but it was dry, although I cant say if it was “hard”, it rasped off, and I could sand it, but it may have been a little chewy, possibly not fully cured after a week or two, so I can only assume a poor mix, combined with no thin epoxy applied first.

      Yes it had quite a load on it, it needed a spanish windlass to draw it in at the stern. So placement was not ideal. Although you’d hope that a scarf would perform better than the wood itself as far as strength goes (perhaps not flexibility). Do you think it will eventually cure?

      So how do you measure it accurately? How much latitude is there? How should one err?

      The two components are vastly different in viscosity and feel, one is almost fluffy and airy, the other slimy, dense and snotty, this makes measuring really tough. My approach is to eyeball the mount sizes, I look at the volume based on a spatula load.

  2. MIchael Jansen says:

    That’s the good thing about wood. Easily repaired. Frustrating none the less. I suspect the Gudgeon Brothers would be able to give a good analysis of the failure – they have a very good web site and will answer that sort of question. I would guess not enough catalyst at first thought, and shame on you, not mixed enough. It would eventually cure, but not as strongly as it should. If you are worried about the mix ratio being right, a set of scales might help. Assuming the two parts are around the same weight, add the first gloop, check the mass, then add catalyst until the mass doubles. Good to find it now, rather than when the sides and bottom are fixed into place!

    • paulatkins says:

      But Michael, it is a pain to mix the thick stuff!!!!!!!
      Scales are a great idea. I’m not sure if it is a weight equivalent though. I will find out, that would be a cool solution.

      Also, the joins will be so buried under layers you will never find them, they are well supported.

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