REFLECTOR: Epoxy and Hardener

Tue Sep 7 09:58:53 CDT 2004

Chuck's explanation seem to be about as good as you can get.

I will add the following two items.  These I picked up from discussions
with Scott Swing.

1) The yellow-brown color comes from a dye in the hardener.  Without it
the epoxy would be clear and can cause problems trying to determine if
the glass is 
properly wet out.  I have used the Velocipoxy to wet out glass.  It is
nearly clear.  I can say that it was not easy to tell if it was
under/over saturated.  I also thought that if the lay-up was thick
enough, lots of layers, it would be very difficult to tell.  The dye
helps.

The dye is sensitive to light.  It turns darker with prolonged exposure.
The color of the dye apparently does not play a part in the integrity of
the epoxy.  In other words, the epoxy can be a very dark brown and still
be just fine.

What seems to matter more is the styrene content.  It is the primary
stink agent in the epoxy.  If you are mixing a batch and your eyes and
nose get a little sting then its probably good.  The hard part is to
notice that the strong smell is not there.  The styrene will evaporate
over time.  Every time you use it the odor might become imperceptibly
less.

As I understand it the styrene helps to soften/etch the glass you are
laying up on.  You notice this most when you put micro-slurry on the
blue foam.  The foam gets soft.  The styrene evaporates as the epoxy
cures and the foam gets hard again.  If it isn't there then the bond is
considerably weaker.

2) The hardener will become thick.  This appeared to be crystallization.
I put the whole bucket in the warmer over night.  The next day it flowed
better but not nearly as well as when it was fresh.  This did not change
the styrene situation.  It was still unusable.

At OSH this year I purchased all the EZ-84 hardener that Wicks had
brought with them.  Left them with four cans of resin.  The guy looked
at me kinda strange and even said "you know you don't have any resin
here?"  "Yeah ... I know"  It came in 1 Qt cans (each half full).
Supposed to go with a full quart of resin.  The cans made immediate
sense to me.  They are completely opaque.  They are very well sealed.  I
don't believe the styrene was going to evaporate by osmosis through the
sides of the can.

I don't know enough about the white plastic buckets the stuff is shipped
in from the factory.  Can the styrene evaporate/penetrate the sides over
time?  It is only a theory, but it makes sense to me.

For now I'm opening the hardener cans one at a time, only as I need
them.  I'm keeping the unused cans in the refrigerator.  I don't know if
the fridge is helping, but the directions say a "cool, dry place."  I
have already used one can that sat in the fridge for a month.  It isn't
doing any harm as the epoxy was great.

I don't have an epoxy pump.  I use a digital scale that reads in grams.
I keep the hardener in a water bottle that has one of those dish soap
bottle type closable caps.  I keep it at room temperature.  I keep the
resin in the warmer.  Keeping the hardener in the warmer seemed to
promote the styrene evaporation.

My two cents.  Well maybe 1.5,

Andy

P.S. Ronnie, do you save all the e-mail on the reflector or just the
gems that I post?  :)

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Chuck Jensen
Sent: Tuesday, September 07, 2004 9:29 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: RE: REFLECTOR: Epoxy and Hardener

John,

Seems like a fair request but its not easily answered, since the shelf
life of many of these materials are dependent on environmental factors
such a light exposure, temperature and humidity.  If the manufacturer
makes the "shelf-life" so short that they cover the worst case scenario,
large volumes of perfectly good epoxy will be thrown away.  On the other
hand, if they extend the shelf-life to reflect perfect storage
conditions, some will proceed using an epoxy that is marginal or worse.

We use tankers full of polymer epoxy for solidification of nuclear
waste. As part of our Process Control Program (PCP), we do test
solidifications with the neat (raw) binder materials.  If the observed
behavior, such as exotherm (if appropriate), cure time and cure state
(dry and hard) is acceptable, the epoxy and all of the hardners and
diluents are then considered to  also be acceptable.  You can do the
same thing.  If the end product is good, you can be assured that the
ingredients are good.  If the end product is garbage, one or more of the
ingredients is garbage.  

Someone more experienced in structural epoxy use may correct me, but if
the cure and end product meets all the visual and physical checks, its
can be relied upon to be a good product.  In other words, the end
product is unlikely to have latent, hidden flaws due to bad ingredients
resulting in a sub-standard product, if all outward signs are
acceptable.  No?

Chuck

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of John Dibble
Sent: Monday, September 06, 2004 10:17 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Epoxy and Hardener

With something as important as the long term structural integrity, I
think an iron clad statement from the factory or the epoxy manufacturer
concerning the effect of age on the epoxy ingredients is in order.

Jim Sower wrote:

> Can't imagine why not.  IIRC someone on the canard list checked with 
> the factory and they said if you put the cap back on the jug it will 
> be good forever.  If years per jug is an issue, I'd have to be a 
> sloooooow builder.  Now if you was to put it in an open bucket and 
> leave it out in the rain ... Let your conscience be your guide .... 
> Jim S.
>
> Ronnie Brown wrote:
>
> >Jim,
> >
> >Does MGS have shelf life of greater than 1 years after opening?
> >
> >My EZ poxy hardener was fine for one year, then started getting dark,
then
> >like molasses.
> >
> >Ronnie
> >

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