Date:         Sun, 26 Aug 2007 17:36:22 -0500
Reply-To:     Max Wellhouse <maxjoyce@IPA.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Max Wellhouse <maxjoyce@IPA.NET>
Subject:      Re: Fiberglass Patch on Bumpers (Part II is long)
In-Reply-To:  <E1IP5Jo-0007Vl-00@pop-canoe.atl.sa.earthlink.net>
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Ooops, I forgot to add a couple of other points

.  If you add too much MEKP, you can actually make a "hot" batch of
resin that kicks very quickly.  I went overboard on the MEKP once
trying to get an end pour on a kevlar slalom kayak to set up quickly
and within the time it took me to go inside and take a shower, I came
back out to find a  charred and smoldering bow of the kayak and me
out $700 to replace the boat(many years ago).  I think the magic
number is about 2% MEKP to the resin and that's hard to accurately
measure in small batches.  Inadequate mixing of the catalyst in the
resin is another problem that can cause problems in curing.  Old
resin that's beyond its shelf life can cause it too and no real easy
way to test for that.

The Gougeon epoxy has a shelf life of over 5 years(the factory has
test batches from 20 years ago that still fully cure, although the
viscosity is a little thicker than the fresh stuff.  The worst than
that happens is the hardener turns a shade of dark red from the
moisture/air exposure and affects the final color of the repair
unless you add resin colorant or Tempra powdered paint(Hobby Lobby or
craft store) to hide it.  Baby powder makes a decent thickening agent
if you don't have access to the colloidal silica and adding milled(ie
very finely cut up stands of fiberglass cut from woven cloth) fibers
not only thicken the resin, they add a lot of strength to a filing of
a hole or other crevice or low spot.

For a really slick surface on your external repairs, you can take
Saran or Glad Wrap and make a "bag" over the repair and then use 3M
masking tape(you don;'t want cheap masking  tape to fail you in this
process!!) to pull at 12 and 6 o'clock, then 3 and 9 o'clock and then
fill in the other hand positions(1,2,4,5,7,8,10, &11) to pull the
minor wrinkles out of the bag.  Once that is done, you get a carpet
roller or some device to roll the air bubbles out of the
laminate.  You'll hear them crackle as they get past the repair
cloth.  If you masked off the area for the repair, be sure to roll
the resin down to the thickness of the masking tape and not leave a
thick ridge there or you'll be sanding a lot more than needed.  I
usually mask several widths out so the excess resin doesn't get
rolled on to a good part of the bumper.  Once you have the air out, I
like to sprinkle baby powder over the Saran Wrap so I can run my hand
over the surface feeling for small imperfections or high spots the
roller may have left.  I built my roller out of a $7 rubber sanding
spindle and a homemade handle.  The cheapie wood ones that roll
screen into frames are okay for small stuff, but will quickly give
lousy results especially if you have a lot of air under your
bag.  Onvce the resin cures fully, you can remove the bag (Saran and
Glad don't bond to the epoxy) and any masking you did and lightly
feather the edges in.  If the surface is too shiny for you, take a
burgundy or gray Scocthbrite pad and dull it down or use steel wool

Remember that all of this procedure has a time limit on it depending
on the resin your use, the ambient air temperature, and the
temperature of the resin.  The last thing you want to have happen is
the resin either getting warm in the mixing container(exothermic
heat, sort of) and not giving you the time to wet out the cloth and
work out the air in the patch.

This process works well if you have relatively smooth curves or flat
surfaces to work on and not so well on areas with multiple ridges or
90 degrees bends.  The process is simply called contact bagging and
is similar to the aerospace technique called vacuum bagging without
the need for suction and manifolds etc.  There's probably a You Tube
video on how to do it somewhere and if not, maybe I should make one.

Well, that was longer than I planned it to be!!

At 06:45 PM 8/25/2007, Max Wellhouse wrote:

>YOur mistake was using an over the counter resin system like
>polyester or isothalic.  MEKP is nasty stuff for the amatuer and
>those store resinshave additives to make them have longer shelf life
>and that translates into weaker bonds and the incomplete curing you
>speak of.  Most likely, you didn't use enough catalyst(MEKP) and it
>may never fully set up.
>
>I would start from scratch and either use a good quality
>epoxy(Gougeon Brothers, System 3 etc.) and then your repair will be
>stronger than the rest of the bumper.  Ask Mike Cullom about my
>kevlar and Gougeon Brothers repair.
>
>DM&FS
>
>At 11:54 AM 8/25/2007, Jeff Lincoln wrote:
>
>>Ok so I finally got around to fixing my cracked bumper. Problem is I don't
>>think I mixed enough of the hardening compound with the other stuff. So it
>>has been two days and it is still a bit tacky. So tell me is this stuff
>>going to set eventually or did I screw it up completely? If I did screw it
>>up what can I do to fix it - just sand it all back off?
>>
>>I tell you this was my first adventure in fiberglass/bondo - it didn't go
>>real good. Oh well I am just hoping it can be fixed or undone in some way.
>>My prep work was beautiful though - I love the Dremel!
>>
>>--
>>Thanks,
>>
>>Jeff
>>90' Carat (Grover)
>>86' (We call this one Parts)
>>85' GL (Preparing for reanimation)