To: baidarka@lists.intelenet.net
Subject: Graphite Filled Epoxy Bottom Coating (Longish)
From: marc_pettingill@juno.com (Marc F. Pettingill)
Date: Fri, 21 Feb 1997 14:58:19 EST
On Fri, 21 Feb 1997 13:03, Kirk Olsen writes:
> marc_pettingill@juno.com on 02/20/97 07:06:25 PM, wrote
>> ... I routinely add 30-40% graphite by volume to the epoxy% ...
[The trailing "%" was meant to be a close paran; ")" -mfp-]
> I use the West graphite in a System 3 epoxy matrix, but only 10%.
>Does the scratch resistance go up with increased graphite content? How
>about handling the graphite/epoxy? I apply with a roller and tip off
>with a foam brush.
I've stripped a whole bunch of forwarding headers from the above, and
Rodger Korn fits in there somewhere, but he disappeared.
(my apologies Rodger) So I can't tell if I'm answering Kirk, or Rodger,
or ... ? Not to worry
Ok, as to my using WEST SYSTEM Graphite as a bottom coating.
Up until the recent discussion here on baidarka-l, I used graphite filled
epoxy for its abrasion resistance and ease of maintenance. I knew
about claimed "low resistance" benefits from the write-up on the can,
but wasn't really that interested. However, it seems that I now have
an opportunity to get a small dose of smarts so that's why I'm pressing
the matter.
Here in Tidewater Virginia, the tidal rivers, streams, lakes, etc are
strewn with underwater hazards that are hidden by the coffee colored,
slightly raised Ph water. The raised Ph also acts like a preservative
of sorts and once in the water wood hangs around for a while, even
centuries. There is all kinds of stuff lurking down there; ancient
cypress
stumps, old pilings, just plain old branches and trunks, often covered
with barnacles. Every time I go into the swamp I get hung up on
something at least once. And it really cuts up the hull if it's painted.
I have found that a thick coating of graphite filled epoxy first off
doesn't
get cut so badly (The hull tends to slide on the obstruction), and nicks
gouges, scratches ,etc are easily repaired and sanded out, without
having to refinish the whole exterior. (BTW, old time guides in New
England used to put a thick coating of shellac on their wood and
canvas canoes for this very same reason.)
I want as much graphite on the bottom as I can get, its the graphite
thats giving the abrasion resistance not the epoxy. So I put as much
graphite in the epoxy as I can just barely get spread smoothly on the
hull. The consistency of the graphite/epoxy is sort of like catsup;
really thick, and so opaque that one coat completely hides the wood
color/grain. It will just barely roll out, and then I tip it. But do get
some
orange peel texture, but no problem, I sand off the shine anyway.
I typically put on three coats of graphite/epoxy.
I use WEST SYSTEM 207 Special Surface Hardener; it is formulated
as a base coat for clear finishing. It is also supposed to have enhanced
flow characteristics which is just what I want with the high graphite
percentage. (Some friends have told me that they have had "flow"
problems using 205 and 206 hardeners even at the 10% level, which
isn't opaque.)
207 has some UV block in it too. As to longevity of the finish, I left
a canoe bottom-up in the sun for a year, and there was enough left
that nowhere could I see wood through the graphite/epoxy. (I think this
is at least three years of "typical" useage.) As I see it, the UV block
in the 207 is protecting the epoxy, as is the graphite. I know some of
the epoxy is ablating because I always get a slight blackening if I wipe
my fingers across the surface. No big deal.
I suppose you could take the claim of "low friction" for graphite to be
connected to the claim for abrasion resistance, but that's not my sense.
My earlier very short quote of the info on the can has probably
strengthened this idea.
Here's a more complete quote (caps and all, exactly as it appears
on the can):
"423 Graphite Powder is mixed with WEST SYSTEMr Brand Epoxy
to produce a low-friction, abrasion resistance coating, commonly used
on rudders, centerboards, and bottoms of racing craft that are dry
sailed."
Now I suppose that "low friction" could have to do with getting the
centerboard into and out of its trunk, or be linked to "abrasion
resistance." but I'm beginnig to think not. My sense is that "low
friction" is connected to the idea of racing and going fast, not
running aground.
I will continue to use graphite filled epoxy for abrasion resistance and
low maintenance, but... if I can get a second benefit by changing my
application or sanding I would like to do so. (Neat, another "added
value" feature that doesn't add to the real cost of a hull.)
I figure if we discuss it in the open, you all can also get such benefits
as it offers too. I suppose there is a "hard skin/soft skin" element in
the equation too, but I am wholly unable to address it.
~marc
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Marc_Pettingill@juno.com --///-- Award winning all-wood canoes
Designer, Builder, Teacher, Author "Building SWEET DREAM"
28 pound, all-wood ultralight solo canoe for single & double paddle
Build your SWEET DREAM at WoodenBoat School Sep 16-20, '97
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