[Rhodes22-list] Re: CB trunk delam update

[Ronald Lipton]

Great explanation.  I, at least, am glad that Lou asked.

Ron
----- Original Message ----- 
From: "Roger Pihlaja" <cen09402 at centurytel.net>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Tuesday, December 14, 2004 11:24 AM
Subject: Re: [Rhodes22-list] Re: CB trunk delam update


> Lou,
>
> Ok, what's going on as epoxy cures?  Epoxy comes from the manufacturer in
> two containers, the resin and the hardener.  The resin consists of the
> monomer or single chemical units that are going to be chemically reacted
> together into a gigantic 3-D molecule.  When about a million monomer units
> join together, the result is a solid polymer of cured epoxy.  This
chemical
> reaction is caused by the chemical in the other can, the hardener, which
is
> actually a catalyst.  As the term catalyst implies, the hardener
accelerates
> the rate of joining or chemical reaction between the monomer units and the
> developing polymer.  However, the catalyst itself is not consumed or used
up
> in this process.  The most commonly used hardeners for epoxy are small
> molecules called amines.  The funny thing about the epoxy system is that
> amines & epoxy monomer are very soluble in each other.  This mutual
> solubility makes it relatively easy to blend the resin and hardener
together
> to start the batch.  But, amines are not very soluble in the epoxy
polymer.
> We won't get into the reasons why, it's a physical chemistry thing; but,
> trust me on this one.  So, as the epoxy monomers steadily turn into a
giant
> epoxy polymer, the molecules of amine hardener are repelled from the
> interior of the developing solid.  Just like oil on water, the hardener
> tends to accumulate at interfaces or surfaces as it becomes insoluble in
the
> cured epoxy.  However, when the epoxy has fully cured, most of the amine
> molecules end up trapped somewhere inside the bulk solid & have to diffuse
> thru a solid polymer in order to reach a surface.  Solid state diffusion
is
> a relatively slow process, requiring 6-12 hours at room temperature.
> Macroscopically, we observe the accumulation of a waxy or oily layer on
the
> surface of the cured epoxy over the 1st day after initial setup.  This
waxy
> layer is commonly referred to as "amine blush".  This waxy layer will tend
> to mechanically interfere with achieving a good bond with another layer of
> epoxy on top of the old layer.  This is why we have to chemically wash
away
> the amine blush with a solvent like acetone before applying another layer
of
> epoxy.  If we keep adding new epoxy on top of the old layers before the
> amines have had sufficient time to diffuse to the surface; then, we can
> avoid this intermediate surface preparation solvent wash step.  There will
> still be reactive epoxy monomer units on the old surface and the fresh
epoxy
> will actually bond at the molecular level as well as mechanically
interlock
> or adhere to the old layer.  By adding fresh epoxy to this green epoxy, we
> achieve a much stronger bond between the two layers than if we allow the
> amine blush to develop & then solvent wash it away.
>
> One of the nice properties of  West System epoxy is the relatively large
> time window available for adding the next layer of fresh epoxy over the
old
> epoxy without having to worry about solvent washing the old surface.  At
> room temperature, the so called "pot life" of the reacting epoxy will be
> about 10 minutes using the 205 Fast Hardener.  From that point out to
about
> 6 hours, fresh epoxy can be directly added over the old epoxy.  If you can
> press your fingerprint into the green epoxy & not peel off any of the
> relatively soft polymer when you remove your finger; then, the epoxy is
> sufficiently cured to add the next layer.
>
> So, to answer your question regarding the cure time for the fiberglass
tape
> flange on the G-10 patch, the best thing would be to laminate the G-10
patch
> into the centerboard wall while the epoxy on the fiberglass tape is still
> green as I've described above.
>
> Epoxy tie layers should NEVER be allowed to fully cure before adding the
2nd
> layer.  Epoxy tie layers should always be used to bond with the next layer
> of epoxy while still green for the reasons explained above.
>
> There, that's probably more than you ever wanted to know about the
physical
> chemistry of epoxy.  Aren't you sorry you asked?
>
> Roger Pihlaja
> S/V Dynamic Equilibrium
>
>
> ----- Original Message -----
> From: "Lou Rosenberg" <lsr3 at MAIL.nyu.edu>
> To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> Sent: Tuesday, December 14, 2004 10:16 AM
> Subject: Re: [Rhodes22-list] Re: CB trunk delam update
>
>
> >   Roger,
> >   Although I just did cut out a 10x5swath of  cb wall, there was a
> > hole from the previous weekend where I was trying  to sand down the
> > bulging area and cracked through the laminate.
> >   Which made me aware that the laminate is of varing thicknesses
> > throughout the trunk.  Actually I mis spoke as it has only been a
> > week since that piece cracked not two wks.
> >
> >
> >
> > >Lou,
> > >
> > >Right off the top of my head, the only other cutting tool that comes to
> mind
> > >would be a small end mill that would be chucked up into the Dremel
> Multitool
> > >using the flex drive.  These cutters resemble the small burrs the
dentist
> > >uses on your teeth when you have a cavity.
> >
> >
> >
> >     I know what you are referring to and will investigate.  The flex
> > drive unit itself is almost the width of  the narrow aft section ,  I
> > ve mounted the flex drive on a strong pc of wood but will have to go
> > to a steel rod next so I can  manipulate the blade into the tight
> > corners.
> >
> >
> >
> > >If you just cut the bad FRP laminate out this past weekend, how can the
> damp
> > >cement behind it have been exposed to the atmosphere & drying out since
> > >Thanksgiving?
> > >
> > >I'm not sure you understood my suggestion re the fiberglass tape.  Let
me
> > >take another run at explaining it.  Imagine you are going to build a
> > >"flange" on the centerboard well side of the G-10 patch.  Up on the
> > >workbench, where everything is easy to get at & nice to work with, you
> > >laminate half the width of some fiberglass tape all around the
perimeter
> of
> > >the G-10 patch.  In effect, you will have built a flange of fiberglass
> tape
> > >that extends beyond the edge of the G-10 patch.  You let the epoxy cure
> to
> > >the green state so the fiberglass tape is good & stuck down & starting
to
> > >get fairly stiff.  With half the width of the fiberglass tape stuck
down
> to
> > >the G-10 patch, the fiberglass tape should behave nicely when you
> laminate
> > >it into position in the centerboard well.
> >
> >
> >   GOT IT NOW!! thanks for the more descriptive picture.
> >
> > >
> > >After putting an epoxy tie layer on the cement, I would fill in the
rest
> of
> > >the void space between the G-10 patch and the cement with thickened
> epoxy.
> > >Press the XS epoxy out around the sides of the G-10 patch as you push
the
> > >G-10 patch home.  The epoxy squeezing out around the sides of the G-10
> patch
> > >will provide the adhesive you will need for laminating the fiberglass
> tape
> > >down to the centerboard well.  As long as you can get in there with
some
> > >sort of small tool, like say a tongue depresser, to wet out the
> fiberglass
> > >tape as the epoxy squeezes out underneath it; then, this technique
should
> > >work slick as a whistle!
> >
> >
> >
> > NEW QUESTION!!*************
> >
> >   Roger,
> >    DOES the tie layer of epoxy has to be cured before I proceed with
> > the G10 patch?
> >    That part of epoxy/glass work is a bit confusing to me..
> >   I will most likely be working in 40 - 45F temps under my tarp here
> > so I am guessing it may take a while for that tie layer to even begin
> > to  kick.   And I assume I need to place plastic under the glass tape
> > so it will not adhere to the worktable wood under it?
> >   sorry to be stating the obvious but you can see we are writing a
> > book here on  "FIBRE GLASS LAY UP FOR DUMMIES!"
> >
> >
> >    I think I might just sand down the other narrow aft bulges with my
> > small grinding tool if I cannot cut it out as that will just take
> > care of the bevel at the same time.
> >
> > >
> > >Your idea of a piece of plastic & a board to hold the G-10 patch in
> > >alignment while the epoxy cures will probably work OK.
> >
> >   Thanks!
> >
> > >
> > >I like the idea of the fiberglass tape around the edge of the trunk vs.
a
> > >simple fillet of thickened epoxy.  With the fiberglass tape, there will
> be
> > >no concerns over strength & it will be absolutely waterproof.
> >
> >
> >    Yeah thats gonna be  an easier job than the trunk but getting the
> > bad FRP our from around the edge is still a big job!  I might see the
> > voids come into play there and will be pokin around to see how deep
> > my driver goes before I hit the hull... yipes7^$#@!!
> >
> >   thanks again Roger!
> >   Lou
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> >
> >
>
>
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