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Re: Wet test of polyurethane glue

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  • Peter Lenihan
    ... wrote: I suspect a couple of things that might be at the root of this ... to be ... specified ... Hi John, I believe your first choice for the root of the
    Message 1 of 8 , Sep 1, 2004
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      --- In bolger@yahoogroups.com, "John Bell" <smallboatdesigner@m...>
      wrote:
      I suspect a couple of things that might be at the root of this
      > problem. First is glue starvation. Epoxy needs a thick glue line
      to be
      > effective. The other issue is that I built the boat as Michalak
      specified
      > with solid timber butt blocks.


      Hi John,

      I believe your first choice for the "root of the problem" is
      the more important one. It has been both my experience and
      observation that so long as there is no glue left in a joint,whether
      due to excessive clamping pressure or well driven screws/nails,this
      joint can hardly help itself but to fail at some point.
      With epoxy,it really doesn't take much to create a glue starved
      joint when using a batch of peanut butter.Applied over bare
      wood,some of the "liquid" in the peanut butter batch will leach out
      and into the wood leaving precious little behind in the peanut
      butter. Obviously the remedy for this is as spelled out by
      Don,of "OINK" fame.That is,pre-wet the surfaces to be joined with
      epoxy,neat, then go at it with the peanut butter batch.
      However, my all time favorite,never-let-me-down, I'd-bet-a-
      years-salary solution/insurance against glue joint failures is the
      not-yet-famous HOLLOW TRICK ! It can be found in the files section
      of this group in the Tricks,Tips etc folder
      The sketch shown illustrates a timber to plywood joint but
      this same method can(should!) be used whenever laminating other
      stuff together too,like plywood to plywood. It really doesn't take
      much and things go very quickly with a nifty little grinder and some
      24 weight Alu-oxide paper.
      Timber butt blocks have little end grain exposed and what
      little there is can easily be sealed,thus the expansion from water
      absorption is not really all that great across the grain and should
      not over-come a "hollowed" joint assembly.
      Mind you, I am refering to sane hard wood timber blocks and
      not some punk wood which has all the properties of a sponge without
      any of its usefullness :-)


      Sincerely,

      Peter Lenihan, big time fan/advocate of the hollow tip,despite being
      accused of having way too much hollow above my shoulders, only
      trying to encourage sound,long-lived amateur built wood boats for
      everyones enjoyment,from along the shores of the St.Lawrence
      River............
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