Building a stitch & glue boat in Fiji

Discussion in 'Boatbuilding' started by Saqa, Oct 20, 2013.

  1. Saqa
    Joined: Oct 2013
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    Location: Fiji

    Saqa Senior Member

    I had a slight disaster with this. My rubrails on one side has let go at the bow. Epoxy didnt bond too well. Surface was prepped with 100 grit garnet at 45 degrees to the grain and after planning. Presence of contaminants is unlikely. The epoxy was thickened with microfibres. The failure length is about 12" and opening further if pried. Should have left the screws in
     
  2. groper
    Joined: Jun 2011
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    groper Senior Member

    Did you thoughrough ly wetout the timber with plain resin before applying the thickened mix? Bet you didn't or it would never let go...ever...
     
  3. Saqa
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    Saqa Senior Member

    Actually I did, but only the bare timber on the rail. The hull it went on was cured glass which where I had planed the fairing epoxy off and rubbed with 80. Screwed every 25cm, no gaps as the rail twisted as well as bent into place
     
  4. groper
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    groper Senior Member

    Well that's very strange... was the mixture too thick perhaps? Too much microfiber and not enough epoxy can be the cause? Otherwise when done correctly, the timber will have to be broken before the epoxy will let go...
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's usually very rare to find a failure that wasn't prep or mixing related. Was the wood wetted out with straight resin before the thickened goo was applied? If not, the raw wood likely sucked out the resin, starving the joint.
     
  6. Saqa
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    Saqa Senior Member

    It was wetted with pre-pack epoxy glue which is made up of epoxy and microfibres and is very runny. I think the failure is flex related. The ply and the twisted and bent lumber dont flex the same. I think it happened after trying to fit a frame near that location that is a hard fit after sheathing the outer hull
     
  7. Saqa
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    Saqa Senior Member

    Btw the glue let go on the glass side
     
  8. PAR
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    PAR Yacht Designer/Builder

    I don't think it was a flexure issue, but a prep or procedural concern. What do you mean pre-pack? Can you provide a brand name and product type as well as the procedure you used for the coating, sheathing and rub rail bond?
     
  9. Saqa
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    Saqa Senior Member

    Brand: Resene
    Product: Epoxy Glue. Comes ready mixed with microfibre.
    Rails 20x26mm damanu semi hardwood ripped planed and belt sanded with 100 grit across the grain. 26mm side is the contact surface and screwed on and hull marked then unscrewed. Hull planed along the mark and hand sanded with 80 grit. Rail painted with glue then followed with a bead along the centre of the contact surface. Screwed back on and wiped excess

    Rails are plenty spingy needs a fair bit of force to lay. One person to push into place and one to screw. Not a one man job. The wood surface shows glue on it and some line patterns of the glass. Didnt adhere to cured resin too well
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Did you remove any blush, before gluing down the rails? Any solvents involved? Were the raw wood rails, wetted out with straight epoxy, before the thickened epoxy went on? If not - well we've found the problem - prep. Any raw wood surfaces need a straight wetout coat of epoxy (no fillers), before any additional epoxy (with fillers) is applied to prevent joint starvation.

    If the previously sheathed hull had blush and you applied your glue, it's possible this was the problem (surface contamination). All epoxy work requires a standardized approach, which shouldn't vary. You can't skip wetout coats on raw wood, you can't ignore the potential for blush, etc. Everyone that's relatively new with epoxy, learns these procedures, usually the hard way. Once you establish what works for you, stick with it and don't vary the procedure. By your description of the rail surfaces, it sounds like starvation, which can also happen if you apply too much pressure during assembly.

    On a rail, I wouldn't glue them down, but if you do, the glue mixture should be quite viscous, being nearly so or completely non-sagging. These mixtures are less prone to starvation, assuming a good wetout prior to applying the thickened goo.
     
  11. Saqa
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    Saqa Senior Member

    hmmmm that defeats the purpose of buying 'glue' if have to wet out with neat epoxy first. The can has instructions to only cross sand and nothing about wetting out with something else first. I spoke to Resenes rep who advised using that for all my wood gluing as it has already been formulated as a wood glue. Its very runny, only slightly more viscous then neat. Lot like honey. I used it both for priming by painting it on then beading with a syringe along the centre on the rail to build up a filler content

    Blush or not enough scouring seems more like it. Only about 20cm of rail from the bow end has come loose and hard to see inside but looks like the epoxy didnt stick to the hull surface that had previously been glassed and given a coat of fairing compound which had been planed off in prep and rubbed with 80. I didnt use any solvents, figured planning off the surface to get down to the fabric would suffice

    For now I am thinking to just inject some more glue in the join and screw back in. The rail is going to get glassed in when I lay the flat ply tops for the gunnels down. Its going to get wood on ply contact on the top face and a wrap which I hope builds up to usable strength

    Could there be some relation to epoxy on the fishing rod wrap cracking at the steel guide feet when a rod is bent?
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Epoxy cracking as you describe on a fishing rod guide, is because of differing elongation modulus in the three materials ('glass, goo and metal).

    Again, all raw woods need a priming wetout coat, because it will leach into the surface a bit (how much depends on species and grain orientation), which draws epoxy away from the joint. Once the joint is wetted out, you wait a little to see if the raw wood has sucked in some goo in spots. If it has, you'd be well advised to apply some more straight epoxy. Once you can see the surface is shinny and no dry spots, then apply thickened epoxy, which usually should be thicker then "runny", if only to remain in the joint when pressure is applied.

    Sanding a blush can remove it, but more often than not will just smear it around and impact it into the surface. This is most common on relatively narrow contact areas, like your rail. All cured epoxy should be washed with a mild soap, rinsed and dried, before sanding for another coat. Lastly, 100 grit is about as smooth as you want for a mechanical bond. I prefer coarser grits, with 80 being as fine as I'll go and 40 - 60 being the usual for me. The more "tooth" the better on this type of bond.
     
  13. Saqa
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    Saqa Senior Member

    Cool, will keep in mind for the work coming up. finally have come to the stage where all the ply and wood for the boat including decks, hatches, supports, console, drivers seat, gunnels have been cut, sanded and dry fitted

    Now to take apart a section at a time to glue, fillet and tape. Cant believe how close to painting I am now

    Also hoping to hear some feedback on the other thread about rolling vs spraying and auto paints. Have to start sorting that out now
     
  14. SamSam
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    SamSam Senior Member

    I can't find any Resene glue, only this ...d808 - Resene Epox-O-Bond epoxy filler.

    Anyway, maybe you tightened the screws too much. From what I can tell, epoxy shouldn't be clamped too much. I think that's one reason for epoxy's popularity, tight fitted joints and heavy clamping aren't needed.
     

  15. Saqa
    Joined: Oct 2013
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    Saqa Senior Member

    I believe its this product rebadged by Resene
    http://www.altexboatpaint.com/ayb_product_details/p/354/c/64/t/17

    I cant figure out how to place sufficient pressure on the timber to get it to mate with the hull shape without screwing it with the screws going in close to each other. Too many clamps would be needed which I dont have. Maybe the damanu or 20x26mm is not the right choice. Thinking about replacing it with slit PVC
     
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