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Working with Epoxy |
‘shop talk
Steve Condon
Working with Epoxy
In this installment of ‘shop talk,
I will describe a few tricks for mixing, thickening, coloring and applying epoxy resin.
Mixing Epoxy Resin
The first important question is what to
mix your epoxy in. A package of 4 ounce paper cups from Price Club can nearly last a
lifetime and the cups are a very good size for mixing small quantities. If you are using a
fast cure epoxy and want to get as much working time out of it as possible, it is best to
spread it out so it won't get hot and go off so quickly. A paper bowl works well for this
(also available at Price Club in mass quantities for a good price).
Another good thing to have on hand is a
good supply of popsicle sticks for mixing. I bought a box of 1,000 at Smart & Final
years ago for a couple bucks and still have about 700 left!
The two most important things about mixing
resin are to get the proportions right and to mix it thoroughly. To get the proportions
right, I use a gram scale for small quantities or the 5 to 1 pumps that work with the West
System resin for large amounts. If you don't have a gram scale or the measured pumps, the
1 ounce plastic cups that you can buy at the hobby shop will allow you the more accurately
"eyeball it."
To ensure a thorough mix job, stir it
until the color and air bubble content are uniform throughout. Then, stir it for ten more
seconds just to be sure! If you plan to add a thickening agent, mix the resin thoroughly
first, then add the filler.
Thickening Resin
There are many choices when it comes to
thickening agents for resins. The first thing to do when choosing what to use is to ask
yourself a series of questions about the application. Is it to fill for contouring, to
create a fillet, or bond for strength? Will you need to sand and fair it in?
For strength, milled glass fibers or
cotton flox will make epoxy very strong when mixed together.
A very common thickening agent Cabisil or
Colloidal Silica, although pretty strong, is really not best for structural support. Use
this when you need to fill for contouring.
West Systems makes a Microlight Filler
material that is designed for use as an easy-to-sand/shape filler. It makes a mixture that
looks like a chocolate shake and when mixed really thick, can create a formable gel. Great
for filets!
Another material that is a good, strong
filler is balsa dust or other sawdust. If you have an orbital sander with a dust
collector, you can save the dust for filling jobs. This works especially well for
repairing boo boo's on natural wood finishes!
Pigmenting Resin
If you want the color of your repair jobs
to match your models color or if you just want to try something different, try mixing some
pigment into the resin (again, after the initial mixing).
I have been successful at blending-in
repairs on pre-colored molded models by pigmenting the resin the same color. This way you
can glass on the outside and it will barely show-up.
Pigments are available as a paste or dry
powder. The dry powder seems to be the most opaque in my experience, although the white
paste pigment sold by West Systems can be mixed for a very opaque result. The powdered
pigments are more difficult to find, but should be available from the stores that sell
resins, fiberglass cloth and fillers, like Diversified Materials (464-4111) in La Mesa or
Squires-Belt Materials (232-8188) in San Diego.
Applying resins
Un-thickened Resin Application
You can use darn near anything, as long as
it's clean. Foam brushes work well for most applications. Cheap paint brushes or
"epoxy" brushes (imagine that!) work well. I don't recommend trying to clean
them when finished; it's simply not worth the hassle or the waste of cleaning agents. Buy
the cheapies and toss ‘em when you're done. For many applications (like sealing a
wood-skinned wing) simply pouring the resin out of the cup and spreading it around with a
squeegee or paper towel works great. For these methods of application (well all of them,
really) I recommend wearing surgical gloves--another good thing to get when you're at
Price Club buying mixing cups.
Thickened resin
There are really four applicators that I
have used successfully for thickened resin:
Popsicle stick. The crudest but
easiest of all application methods since usually that's what you mixed the stuff with, and
it happens to be in your hand. The crudest but
easiest of all application methods since usually that's what you mixed the stuff with, and
it happens to be in your hand.
Plastic syringe. The most precise way
to apply it, but also the most expensive. Hobby shack sells a Monoject plastic syringe
with a slightly hooked nose for about $2.50. They work great and can be cleaned (after the
epoxy dries) and reused many times. The most precise way
to apply it, but also the most expensive. Hobby shack sells a Monoject plastic syringe
with a slightly hooked nose for about $2.50. They work great and can be cleaned (after the
epoxy dries) and reused many times.
The next time you're at the dentist, see
if he or she will give you a few of the same Monoject syringes which they use for a
variety of things.
Baggie with the corner precisely
cut-out. This method follows the technique bakers use to put frosting on cakes out of a
bag. Cut as big of a hole as the bead you need and twist it up and squeeze as you go. This
works best when dispensing large amounts. with the corner precisely
cut-out. This method follows the technique bakers use to put frosting on cakes out of a
bag. Cut as big of a hole as the bead you need and twist it up and squeeze as you go. This
works best when dispensing large amounts.
Your finger with, or without a glove
(depending on how perfect you want it) will make an excellent fillet. Try wetting your
finger with a little isopropyl alcohol to do a final smoothing. with, or without a glove
(depending on how perfect you want it) will make an excellent fillet. Try wetting your
finger with a little isopropyl alcohol to do a final smoothing.
Some final words
Finally, the most important thing to
remember when using epoxy resins is to keep the mess contained and/or clean-up right away
so you don't: 1) glue your mixing cup/stick to the work surface or 2) glue your wing to
the workbench!
And, always remember to have fun and be
safe in the shop.
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