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Does epoxy spoil?


#1

I have some two part epoxy I use on occasion for pearls. This last
time I used it the pearl came loose. I went back and examined the
mixing tray I used and it showed the stuff to be seperated and part
of it still wet after 4 days. Even the hardened part pulled right off
the plastic tray I mixed it on. I mixed a new trial batch and it
hardened but the hardened stuff pulled of the tray again in a mass.
Shouldn’t the glob also have been permanently glued to the tray? (I
just use the lids to old margerine containers as mixing trays). So
the question is, does epoxy spoil/go bad?
NET


#2

Yes they do go bad, some types faster than others. As to the stuff
not hardening, sounds like it wasn’t mixed well as a second try did
set up. A common rule of thumb on mixing this tort of stuff is “Mix
until you think it is mixed well enough then mix it again”. Also,
not getting enough catalyst will cause it to not set up. As to
peeling off of the plastic lid, the lid most likely had mold release
either in the plastic on on the surface. Silicone, teflon and many
oils are all pretty good releases for most epoxies.

John Dach
MidLife Crisis Enterprises
Cynthia Thomas Designs
Cynthia’s sculptures are at: http://www.mlce.net


#3

Your mixing tray is probably made from Polyethylene (PE). Epoxy does
not stick to PE. In fact practically nothing sticks to PE. It’s almost
as good (bad?) as Teflon in this respect. Yes! epoxy can go bad over
time, especially if you leave the cap off or expose it to high
humidity for a long time. It sounds like yours is still O.K. because
the last batch hardened. If there is any doubt, replace it with new
stuff. It can’t cost more than $2-3 . Regards …Bob Williams


#4
  1. Epoxy in sealed containers can stay viralent for many years.
    However exposure to the atmosphere can cause critical componets to
    evaporate in some brands.

  2. Epoxy has a hard time sticking to many plastics, especially if
    the plastic is very smooth like a platic lid. The same goes for glass
    in alot of cases. Epoxy works best on these surfaces if the surface
    is very well cleaned first, and then roughened with like sandpaper to
    give the epoxy something to grab onto.


#5

Hi–I’ve also recently had epoxy troubles. Stuff just wouldn’t
harden/set. I was told an oily residue somewhere in the process was
the likely culprit–since you’re using margarine containers, this
might apply to you. Maybe do a test with a diff. mixing surface? Make
sure your pearl is truly clean before re-attempting it, too. As for
the epoxy popping off th eplastic surface, this doesn’t surprise me at
all. Several brands of epoxy are sold with little plastic palettes &
mixing spatulas, which are designed to be used again and again because
when you bend the palettes the epoxy pops off. I haven’t re-tackled
my mess yet; hopefully we’ll both have better luck in the next,
oil-free, round. Regards, Andy.


#6

G’day Sharon; the quick snappy answer to your question is NO! - at
least not in a reasonable time; say a couple of years…

Epoxy does not adhere to a number of modern plastics such as
polythene, polypropylene PVC, PVA, and in fact any plastic with a
waxy/flexible feel to it. Or rubber. To mix your epoxy resins, use
a bit of tin lid, a piece of flat metal, a bit of window glass, etc;
the epoxy will stick to those, but not if greasy. But you can peel the
set ‘glob’ off the wax-like plastics and use 'em again. Does that
solve your problem? Oh yes, remember that you can colour epoxies with
many pigments and dyes,: I use those jars of powder of the type used
for children to paint with. I find the three primary colours plus
white and black will allow me to match any colour I need. I also use
wood sanding dust to colour epoxies for filling cracks in timbers.
Wood sanding dust also makes the epoxy more viscous, and less likely
to run. If you want it to set quickly, put it about 10 inches below a
table lamp. Or put it in the airing cupboard above the hot water
cylinder. (I start yeast off for home brew in there too!) Cheers, –
John Burgess; @John_Burgess2 of Mapua Nelson NZ


#7

Epoxy does have a shelf life. Usually a couple years. If it hardens
completely though, then it’s working fine. If part was soft and part
was hard, blame your mixing. Not mixed well enough. It’s easy enough
to miss a little bit on your mixing surface.

As to the margarine lids, while they’re a nice disposable surface,
epoxy won’t stick to it. Nylone, teflon, plastics like that, can be
hard to glue with epoxies… Plus, chances are, your lids are nowhere
near chemically clean. Through the dish washer, I’d expect films of
either soap or the water spot preventing rinse additives, for example.

Be aware, also, that many epoxies are quite sensative to having the
right proportions of the two resins. With some, that specify equal
parts, if you’re off by as little as ten percent, the bond strength
can be cut in half or more. The best bet, for critical joints, is to
weigh the glue. I use a small carat scale on the bench. Put a piece
of paper (I use 3 x 5 index cards) on the weighing platform, and tare
the scale. Dispense one resin, tare again, then dispense the second
resin in the same amount. since typically one resin is more viscous
than the other, it can easily appear that you’ve the same amount,
when in fact you don’t.

Hope this helps.

Peter Rowe


#8

The product we use requires accurate mixing, 1 part catalyst: 7 parts
resin by weight. To ease mixing, we pour the catalyst into a half pint
soft plastic bottle with a dropper spout and cap. The resin goes into
a quart bottle with an easy pouring spout and a good screw top. The
gallon cans are opened only when the bottles need refilling. Mixing is
done in a disposable plastic or paper shot glass. The glass is placed
on the tray of a digital scale set to an accuracy of .01 oz. The
weight of the container is tared out and the proper ratios are
poured. Thorough mixing is done with a clean spatula. Parts to be
joined are also meticulously cleaned. The glass is saved to check the
cure of what remains on the bottom. It is then discarded. Incidentally,
any epoxy can be made less watery (thixotropic) by adding finely
ground limestone (available at home centers and nurseries). It will
change the color to opaque white. Any powdered color can then be
added. If you are going to do this, first thoroughly mix the epoxy
then add limestone until the desired viscosity is achieved. Add a
little and stir, add a little and stir etc. Then add coloring powder
and mix again. Almost any viscosity can be produced. It can be made to
hold a shape, adhere to a vertical surface and even adhere to the
bottom of a horizontal surface - all without drooping. I’m sure some of
you will come up with new ways to use epoxy and with solutions to old
problems. I’ve learned an awful lot on Orchid. This is partial
payback. Thank you, Ray Grossman Ray Grossman Inc.