Wax Injecting issue

Ok to start off I have to say I am totally new to casting I have
been practicing and I am having a issue with injecting wax into my
rubber molds. I use a hand pump to inject the wax ( The cheap wax
injector from swest) anyway when i inject the wax there’s a place
where some raised letters are. These do not fill with wax. so I get
a wax model that looks good but the letters are mostly missing. What
can I be doing wrong? I also have alot of trouble with the wax
sticking like glue to the rubber. Any help would be greatly

First of all, you need to use a mold release - traditionally, people
use talcum powder (unscented baby powder, in the drugstore, maybe) -
there is also a silicone mold release in a spray can. We use either
or both. Get a small, soft paintbrush and put some powder in a
shallow bowl, and just dust the inside of the mold. Most people slap
the two halves together to knock off the residue - you just want a
"dusting" , not more. This will help you in two ways - it will stop
the wax sticking - and the wax will flow better than you might think

  • it actually lubricates the flow of the wax. I, too, have had
    models with lettering that doesn’t want to fill completely - it can
    be hard to do, depending on the model. Using powder might actually
    solve your problem. Otherwise - a mold is about plumbing - we call
    it sprueing, but it is plumbing. The wax is having to go forward,
    into the mold, and then move at a right angle to fill the letters.
    (The forward movement has to fill almost completely before the wax
    goes to the sides) Sometimes the body of the piece is chilling
    already, and is too bulky for the sideways flow to occur. Anyway, it
    can be a hunt for clues to solve it, sometimes. Possibles: first,
    make sure the letters were truly bonded in the model - look in the
    mold and make sure there are no flashings around the bases - if there
    are, get a hot tool and melt them back (if silicone mold you have to
    clip it) Make sure your sprue rod is big enough - you can melt or
    clip that bigger, too. And then, you can make the wax hotter (but
    don’t burn it), and/or turn up the pressure. Just remember it is
    plumbing: The sprue rod, then the main body becomes a “pipe” to fill
    the rest of the piece - think about how everything gets a flow of HOT
    wax - cool wax is a plug

I would bet that air is trapped in those letters, preventing the wax
from filling the space. When you’re new at cutting rubber molds, it
seem insane to take your scalpel and cut through part of your
design, but that’s exactly what you have to do to cut in air vents.
Try to choose a good location, such as the deepest part of the
design, or a sharp corner, but depending on the design, just a poke
with a supremely sharp blade in the right location will cure your

Good luck and enjoy! I’ll bet there’s not one caster/mold maker on
this entire forum who didn’t experience the same thing when starting

Tess Headley

In order to get raised letters to fill in it may be necessary to
vent the molds, Assuming that you are using either a Vulcanized mold
or the Ferris see through mold compounds , usually wax won’t stick to
Vulcanized or RTV silicone, try lowering your wax temperature and
increasing your pressure a bit. I remember when we still used hand
pumps that we also used mold clamps rather than trying to hold the
mold between pieces of 1/4 inch masonite or aluminum, We recently
experimented with a blue carveable injection wax from Rio Grande
that gave us lots of problems with sticking to nearly all our molds
even the silicone and temperature didn’t seem to have much effect. Rio
does make some clamps to hold your molds together and they work
reasonably well, but the first thing I would try would be lowering
your wax temperature, then vent the mold by cutting with your scalpel
several lines just cutting in to the edge near the top and out to the
sides cut about 1/3 to 1/2 way through the half of the mold then use
jewelers talcum power or in truth any un-perfumed talcum dusting
powder in these vent cuts. Another good wax that we Have used is the
westcast pink from Rio. Is has good memory injects nicely at moderate
pressure, and has a pretty quick set time we use it at about 135 to
145 and sot everything from thick conchos to Filigree brooches And
rings the only drawback to this wax I Have found is it’s a wee bit
hard to read for old eyes. First though I would check your wax
temperature, and do the vents also hold your pressure a little
longer. You can get a candy thermometer pretty cheap , just don’t try
to set your vulcanizer temp with it (they break)

Good luck
Ken www.chickasawsilver.com

If you can, turn over the mold while injecting the wax so the
letters will fill. If this doesn’t work, powder the mold surfaces
with corn starch or talcum powder to make a way to the air to get
out. Also you might try to pump a bit harder to force the air out.
If you are using a mold clamp ( your should) try not clamping the
mold so tightly. If all of this doesn’t help, you may have to cut
air vents from the letters to the outside edge of the mold to allow
the air to escape.

The powdering will help the wax to release. We use a shaving mug
soap brush to apply the powder but you can use any good small
bristled large brush or you can use a puff (relatively fine
mesh/weave bag with powder inside and just "puff/pat the mold
surfaces to dust). Some folks use a powder puff (body powder
applicator puff). Lightly blow off excess with breath or compressed

If you can get the air bubble problems fixed without the use of the
powder, a good spray on mold release (Smooth-on Universal Mold
Release for one, but there are MANY out there) can be used for wax
release. If you are using vulcanized molds, there seems to always
be a problem with the wax sticking in the tapered injection nozzle
hole. But I have found that if you use a type of washer called a
"fender washer" (a washer that is large compared to the size of the
hole, ie. a 1.25" washer with a .25" hole) available at a good
hardware or auto parts store, putting this washer on the mold where
the washer hole lines up with the mold filling hole and then putting
the injector nozzle in the washer hole and filling the mold with
wax, the wax doesn’t stick so badly in the filler hole. This works
best if you are using a spray release (often/usually a silicon
material) but be sure to always release the 2 sides of the washer or
the wax really will stick to it.

Also, some waxes work better than others for different applications.
I prefer Serria Red ( and just because somebodies wax is red doesn’t
mean it is the same as Serria Red. Many like more flexible waxes
that the SR but I like it for cleanup and if any rework is needed (a
well cut/made mold will keep this to a minimum, but the key words
here are “well cut/made mold”).

If you still have problems, re post or write me directly and we can
talk more as to what your problems may be and what to do about

John Dach

I have experienced injection wax not filling details. Instead of
sharp edges on the wax pattern I had rounded edges. My solution was
to inject at a lower temperature which is counter intuitive. You
would think hotter wax would flow better and fill the small details
better. Not so. Hotter wax will produce less detail and air pockets
on the surface of the wax.

The hotter the wax, the more it sticks to the mold. Do not allow
the wax to stay in the mold any longer then necessary. The longer
the wax stays in the mold the more it will stick.

I put talcum powder in an old sock. A couple of taps on the inside
of the mold with the sock will put some powder on the surface.
Residue powder can be blown out. I find it is best to have a heavier
powder coating on all the parting surfaces, (not the design
surfaces). I feel this provides minute gaps in the mold parting
surfaces to allow the air to be eliminated. The use of a small
brush, as mentioned on a previous post, to put powder on the parting
lines is a great idea. You learn something new from orchid every

I agree with Tess. You may have to cut lines into the design to
provide a path for the air to escape.

My 2 cents.
Lee Epperson

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I took all of your guy’s advice and lowered my wax temp to just above
melting and I also used talcum powder on the mold and they are now
comming out great. Thanks a ton. I never would have thought that
lowering wax temp would make a better model but it does. I guess i am
kind of a all out guy I tend to turn everything up to the max setting
and heat the hell out of it but in this industry that doesn’t exactly
work. Thanks again for all of your help folks.

1 Like

I read this thread and it covered almost everything I could think of
and add some. I never would have thought of lowering the temp of the
wax. I have lowered pressure and that has worked. Thanks Orchid for
new insights. Here are a couple of things that no one else mentioned
that I thought I might add to this very productive thread. 1. Use
corn starch instead of talc. Talcum powder is a mineral and cannot
be absorbed by the body. It builds up in the lungs just like coal
dust. Not good. Corn starch can be absorbed as it is organic. It
works just as well as talc. 2. I sometimes use a #62 drill bit to
vent a specific area that is giving real trouble. It leaves a little
nipple that is very easy to clean off . I find that knife vents can
sometimes lead to mold distortion if cut too deep. The drill vents
are less intrusive to the rest of the pattern and much more spot
specific, although they do need occasional cleaning.