[Rhodes22-list] Re: CB trunk delam update

[Lou Rosenberg]

>Roger,

  I can use all the extra creases in my cranium these days, &NO   I am 
not sorry I asked, but still am much in  gratitude for sharing your 
knowledge!
  peace
  Lou


>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
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>>
>
>
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