Date: Wed, 7 Feb 2007 12:24:15 -0600
Reply-To: Max Wellhouse <maxjoyce@IPA.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Max Wellhouse <maxjoyce@IPA.NET>
Subject: Re: Comments on plastic repair/Epoxies in General(a little long)
In-Reply-To: <1EDB3731-9FB2-4858-B367-1A48501C357A@knology.net>
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Jim and Listees: I have posted anecdotally on several occasions
about this strain of adhesives. Although I'm not a chemical
engineer, part of the confusion with this stuff is that people call
anything with a two-part mixing step "epoxy", whether it comes in a
black or clear syringe, two metal cans, or a block of putty you mush
together to get it to kick.. The Plastic Welder series of adhesives
are based on a compound call methyl-methacrolate and yes it does
stink. If you are unsure of whether you are buying a plastic welding
glue or epoxy, read the fine print on the back of the placard in
which the syringe is stored. If it mentions Amines etc, it's more of
an epoxy. If it mentions, methacrolate or methyl-methacrolate, well.....
The Plastic Welder Jim used so successfully is marketed by several
different companies, but the most accessible is the Devcon Plastic
Welder sold(and sometimes mis-stocked) at Wal mart. to the casual
observer/shopper at WM, these syringes pretty much look all the
same. More on that later. The 50cc syringes are a whopping $2.27
each!! Napa/AutoZone/Checker/etal as well as Walgreens etc. sell
this stuff under various brand names, but charge considerably
more. This product claims to have a breaking strength of 3000#, 90%
of which occurs after 30 minutes of curing. Full cure in 24
hours. Clamping/pressure/weighting the bond can improve the bonding
strength for sure. You have to work quickly with it, especially in
hot weather, so mixing only what you will use in 5 minutes is the
key. It doesn't hurt to sand slick surfaces and clean foreign
material from the bonding surfaces as well. My guess is that the
methacrolate actually melts part of the bonding surfaces and that's
where the "weld" part of the product description comes into
play. The super duper expensive version of this stuff is made by a
company in New England and is called Plexus. For those of you
needing a color match on your repairs, the Plexus is a gray color,
but not worth the extra cost for my needs. I uasually travel with a
syringe of the Devcon stuff even though it's so readily
available. My 50cal. metal ammo box holds all my other epoxy and
kevlar repair stuff.
At some point I intend to experiment with some resin colorants I have
for my Gougeon Brothers epoxy by mixing them into the Plastic welder
to see if coloring the adhesive weakens it's bond. I pretty much
know the answer to that before I do it, but my supplier says 1-2% by
volume is all you should use with polyester/vinylester, and epoxy
resin systems, and I have a feeling even mixing all 50cc of the
Plastic Welder even for a small repair, adding just .5 cc of resin
colorant would be hard to measure and likely wouldn't change the
color substantially anyway. Black may be an exception. Really small
amounts I would think to be impossible.
I have successfully bonded 1.5"x4" polycarbonate plates (with 1.5"
metal D-rings in the middle of them) to the vinyl interior skins of
ABS and kevlar/fiberglass canoes. In the years in which I outfitted
whitewater boats for a second income, I never had one of these plates
pull up and they took some serious stress(anchoring thigh straps) and
taking major trauma when the boat struck rocks beneath the water's
surface(hull flexing, not actually having the rings on the outside of
the boat!!)..
As for the other adhesives called epoxies, there are some caveats as
well. The "5 minute epoxies" set up quickly, but read the fine print
on most of their packages, most of the quick setting epoxies are not
waterproof. Even my beloved Gougeon Brothers epoxy doesn't tolerate
high temperatures. I tried to repair a steam gun for a clothing shop
once and the steam pretty much melted the epoxy down. It was a
plastic repair, but prior to me discovering the Plastic Welder
stuff. I would've loved to try the PW on the high temp
application. As a general rule, the epoxies and fiberglass resins
you buy off the shelf have to compromise bonding strength for shelf
life. Polyester and vinylester resins require a really nasty
catalyst called Methyl Ethyl Ketone Peroxide(MEKP). Not only does
the resin have an offensive odor, but the MEKP finds its way into
your eyes, you can go blind. The epoxies cost more, but usually bond
better and most don't have the odor issues. Without adequate
ventilation, a respirator should be worn regardless of odor or
not. The Gougeon engineers test their resin for shelf life and have
samples from 20 years ago that still have 90% bond strength, they
just get more viscous with time and wetting out densely woven cloths
becomes difficult getting all the air bubbles removed. The hardeners
tend to absorb moisture from the air and with time and change color,
but their shelf life would still be adequate. I have hardener that 5
years old and severely discolored, but still kicks when its supposed
to. If I have a repair that needs to be clear, I'll use fresh hardener.
None of these adhesives will bond polyethylene, as it needs to be
"welded" with a "hot air" plastic welder and I never got the hang of
that. Old Town Canoes sells both a "repair" kit and a "grunch pad"
kit for its Discovery line of cross-linked polyethylene canoes, but
that urethane-based resin system is very expensive, has a very short
shelf life, and kicks very quickly after mixing. You also have to
"polarize" the plastic surface to be bonded with the brief passing of
the inner blue cone flame of a propane torch to get the urethane to
bond to the poly. I hated fixing those boats!! Cheap to buy, but
expensive to repair
The last item I'd like to mention is that the polyester and
vinylester resins are really difficult to tell when they're "over the
hill". By that I mean their shelf life has come and gone. I once
used old polyester to try to fix something and even though I used 4%
MEKP, 6 hours later the repair is still gooey at 60 degrees F. The
point is, you can't look at it and tell whether it's still good or
not and cleaning up all that gooey crap and starting over again just
isn't worth it. Hopefully you novice"bonders" out there know a
little more about all this stuff now.
.
So much for that epistle.
DM&FS
10:08 AM 2/7/2007, Jim Felder wrote:
>For those of you who have tried to used epoxy to repair broken
>plastic items, you've probably been underwhelmed at the results,
>especially when gluing together chipped and broken pieces (bonding
>one flat surface to another usually works fine, it's the pieces that
>crack through and need repair that seldom hold).
>
>Yesterday, a four-legged passenger jumped into a front seat and
>damaged an open cup holder. As much as the OEM holders cost, I
>thought I'd pick up some epoxy and give it a try, but I didn't expect
>much as I had not had good success in the past when the pivots broke
>off of the lower part of the holder.
>
>One of my FLAPS had something called NAPA Plastic Welding Systems.
>Don't use it in a room you're going to be breathing in! It REAALY
>stinks. It is a 2-part epoxy, of course, and it dries a milky white,
>so I used as little as possible on the black cup holder.
>
>In a couple of hours came the moment of truth... would the repair
>withstand being forced over the protruding hinge pins? It did. I put
>a little silicon lube in the joints and on the metal spring plates,
>and the original "snap" came back the holder, all ready to go back in
>today.
>
>For stuff like repairing heater vent covers and broken off heater
>valve cover pins, where strength is required but not much bonding
>surface is available, it looks to be the stuff.
>
>Jim
>
>
>
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