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By this time the second batch on
the table had cooked. Not a good day so far. I mixed up a batch
of resin without filler and rolled it on the surfaces I intended
to do that day. The idea being to let it fill the weave, go sticky
and provide a substrate that might finally work.
The penny dropped when I saw the bubbles…
bubbles?!? On the resin I had just rolled was a perfect little
bubble, and another... and another. That and a look at the close-up
photo I had taken earlier confirmed. I had been proceeding under
the assumption that the problem was the trapped air in a surface
depression of the laminate was not being successfully displaced
by the resin and surface tension caused the pit to remain, more
a mechanical issue. But the size of the bubbles indicated that
idea wrong. Where was the gas coming from? Was it evacuating
from the core itself? And if so, can't water go in the same way
the gas comes out? Or was it gas that had been trapped in the
laminate? Possibly, but wouldn't all that gas have been evacuated
by the second coat of bogg on this last application? Outgassing
through screw holes or cut edges.. yes, but out of the panel
surface? How? So back to the instruction booklet that came from
ATL with the panels. I could find no mention of outgasing at
all and no reference to them being waterproof. The closest relevant
information I could find was from page 2; "The panels are
designed to provide a fair surface on the hull exterior, and
while the builder may choose to add laminate for aesthetic or
other reasons (authors emphasis), it's not required
structurally."
So it may be that the panels are intended
as a structural unit only? I shot off an email; "are the
glass fibre and epoxy skins on either side of Duflex panels waterproof?"
My question must have got lost, no response. That was the last
I ever heard from ATL composites where I had always received
a timely response with any technical enquiry prior to that question.
An update to this question as of
Nov 1st 2011; I have reports from two credible sources of failure
of the surface on bridge decks of two boats from well known designers
using duflex panels that resulted in absorption of water into
the balsa core. One boat was bought cheap and the new owners
stripped the deck underside of outer laminate and balsa core.
They replaced the core with foam, glued in place by vacuum bagging
and then relaminating. The other craft was also reported to have
been sold very cheap and it's repair is pending.
Also; an apparent astro-turfer (spruiker)
for the panel producers reported to have claimed on the web that
duflex panels are indeed structural only, not intended to be
waterproof and "everybody knows that". They do now
but in context the inference is that has always been the case.
The author of this article challenges that and would like to
see a widely published account where that is stated that can
be verified to have been made public prior to this published
article.
And more.. just got a email from
a would be builder who reports he has just taken his duflex panel
kit to the tip... no joke. The stuff was so bad he couldn't work
it and and no one was willing to give even a fraction of his
cost for the partially assembled boat. Approx $50,000 thrown
away. Besides the porosity, delamination had occurred that prevented
faith in the finished product regardless of effort in build so
he cut his losses.
To add to the confusion, I asked a reputable
builder specialising in other core material about the problem
and he felt the same as I, that balsa by itself should outgass
like crazy but was surprised it might go through a layer of heavy
glass and epoxy. I have asked two other builders who have worked
with Duflex panels and they said they didn't have any outgas
issue at all, they never took it into account, and then another
builder who said it was a common occurrence but he figured it
was the gas trapped in the laminate expanding from the heat of
the exothermic reaction. hmmm?
The portion or work that I had done that
was good and I attributed to the tooling was done at night, under
lights when the panels would have been absorbing gas rather than
expelling it. The panels have to be worked on a downward temperature
curve to beat the problem. Even late afternoon wasn't cool enough
to prevent it for me. All bogging from now on will be on the
night shift. Hate the night shift!
That takes care of future work but what
should I do to insure the first hull won't absorb moisture through
the pitted surface? I have to settle the question of whether
it's the core or laminate that is the source of the gas. So I
unpacked my microscope, (doesn't everyone have one?) and grabbed
the first piece of scrap that could be cut to fit the instrument
without waste. I took a couple pics with my scope camera and
they are displayed here. It does show the gaps in the surface
from shortage of resin go about half way through the laminate
though no obvious portals into the core are visible to me on
this sample. Though interesting, this is inconclusive.
I post the pics for reader interest. I wished I had spread a
light coating of resin over every panel prior to assembly, when
they were flat. (and cool!) I notice that the laminate on my
19mm panels for my bridgedeck floor are fully covered in resin
and smooth.
Before I proceed with the first hull I
will conduct an experiment to find out conclusively where the
gas came from and how to approach the problem from there. I'll
post it to the web site building log after publication.
So… taping on the inside of the hull
panels, the first step, can be done with virtual impunity. Any
outgassing would vent freely out the back side. Taping the outside
joints should be monitored closely as they set. Watch the screw
holes! Bogging should be done at night in summer or at least
late afternoon in cooler seasons. Makes me wonder how pro operations
do that with a normal work shift?
Final fairing will be done when the sections
are assembled and sheer finalised but I plan to go as far as
I can in units and stall assembly as long as I can.
It is frustrating having to interrupt the
process for publication, it always seems to be at the worst time,
just as a rhythm is developing
The Update! The experiment to answer
the question... is it outgassing from
the core??? |
