Things You Should Know
1.) Gloves: You're always going to want to have latex gloves
on while working with rubber, resins, and pouring molds.
2.) Be Carful, don't spill: Of course, no brainer, right? Well, this is just
a heads up because none of us want resin to cure on our garage floors or the
wife's extra table that you're using to pour your molds. :)
3.) Ventilation: Remember that we are working with chemicals and inhalation of
emmited fumes in an enclosed area is not good for you. Open your garage or shed
doors, and if you really want to be safe have a fan going.
Tips for Successful
Once you’ve selected the correct material and determined
how to properly use it, you’re on the way to making good
flexible molds with silicone rubber. The following recommendations
will further insure your success.
De-airing is recommended for all silicone moldmaking rubbers
when not using automatic dispensing equipment. The small air
bubbles that result from hand mixing can become trapped in the
mixture and, if not removed by de-airing, can interfere with
exact surface reproduction.
Because the mixture of base and catalyst will expand during
de-airing, it is important to use a container that is between
3 and 5 times the volume of the material itself. The lower-viscosity
silicone moldmaking rubbers such as Dow Corning HS III RTV high
strength silicone rubber and Dow Corning 3110 will expand the
most, up to five times. The higher viscosity silicone rubbers
such as Silastic E, J, M-2, and L will expand the least, approximately
2-3 times the volume.
The mixture can be quickly and easily de-aired in a standard
vacuum chamber. This important step usually takes just a few
minutes. Place the mixed silicone under vacuum at 29 inches of
Hg and hold it there until it completely expands and recedes
to it original level. Time required to complete de-airing depends
on the size of equipment being used.
Thinners can be used with all Dow Corning silicone moldmaking
rubbers. Dow Corning 200 Fluid acts as a thinner of viscosity
for the unmixed silicone. It will have a tendency to slightly
lower the hardness of your cured silicone system a little bit.
The 200 Fluid can bleed from the cured rubber if too much is
added to the silicone, therefore we do not recommend exceeding
10%. The 200 Fluid will decrease the viscosity of the rubber
and make it easier to pour.
Mold Life Extension
Reconditioning. The 200 Fluid can also be used to
rejuvenate the mold surface to extend the mold life of the rubber.
Casting resins will eventually dry out the oil that is within
the silicone moldmaking rubber and by wiping a thin coat of the
200 Fluid into the mold prior to it completely breaking down,
it is possible to rejuvenate the mold surface and extend the
life of the mold. Rub the mold surface with the 200 Fluid and
then wipe the mold surface dry with a clean cloth to remove any
excess. Let the mold sit overnight.
Bake Out. A “bake out” is recommended
to remove the hardeners, plasticizers, and other materials that
leach out of the casting materials and are gradually absorbed
into the silicone molds. A slow, gradual bake out at 200F for
eight hours or a rapid bake out at 400F for two hours can be
used. This will draw silicone oil from within the mold back to
the surface extending the life of the mold.
Release agents are sometimes required for easy removal of some
types of pattern materials that may occasionally stick. Silicones
typically only stick to other silicones and will not typically
adhere to any other materials. Dow Corning recommends using a
thin layer of melted Vaseline to prevent adhesion between silicones
and other difficult to remove pattern materials. Do not use
a silicone mold release for it will act as a primer and promote
adhesion to another silicone or your pattern.
Tips for Successful
As with all chemicals, you should always read and follow all
of the safety precautions prior to working with the materials.
Read all the safety precautions found on the Material Safety
Data Sheets, printed on the bottles, and in this catalog before
working with the materials.
Keep Alumilite out of the reach of children, do not
take internally, and do not use in any way other than it’s
intended use. Even though it has very little odor, we still
recommend using Alumilite in a well ventilated area. Safety
Before mixing make sure you know the proper mix ratio of the
material you are using. All of the casting resins are 1:1 by
weight and/or by volume.
You must mix at least a half an ounce of each side to ensure
you have a proper mix ratio. If you measure out 1/4 of an ounce
of A in one cup and 1/4 ounce of B in another and dump the A
into the B you will be off ratio due to the residue left in the
A side cup. In larger amounts of resin batches, this will not
be enough to throw off the mix and cause an issue with the resin
setting up. But with small amounts of resin (1/4 oz of each side)
this will be enough to effect the mix ratio and will typically
result in parts that appear darker in color and remain soft (never
Once the materials have been measured out in separate cups,
the preferred method of pouring one into another, to decrease
the amount of air introduced, is to pour the A side into the
After the materials have been poured together, mix vigorously
(keeping the stir stick in contact with the bottom of the cup
- reduces air from being introduced into your resin) for approximately
15-25 seconds. Make sure to scrape the sides and the bottom of
the mixing cup.
Once the material is thoroughly mixed, pour the resin slowly
down the side of your mold cavity. Tilting your mold will prevent
the resin from splashing in the bottom of your mold and creating
unwanted air bubbles that would then need to find their way to
the top of the mold. Similar to tilting your glass as you pour
a beverage rather than letting it splash off the bottom creating
Squeeze the brim of the cup to form a point. This will allows
you to pour a smaller stream of resin into your mold controlling
the flow and reducing the chance of unwanted air bubble entrapment
against the surface of the part.
If your mold has undercuts, pour enough resin into the mold
to fill it half way. Then, tilt and rotate the mold in the opposite
direction of the undercut to allow the air to escape up the side
of the mold. Squeezing or burping the mold at the same time will
also help relieve the air trapped in the undercut and allow the
bubbles to release from the mold surface. Once you see air bubbles
come to the surface of the resin and you can be confident you
have removed the air from the undercut, simply top off the mold
by pouring the remaining resin into the mold.
To increase the open time of Alumilite resins, simply place
the “A” side in the refrigerator for approximately
30 min. before pouring. This will increase your open time by
30-60 seconds. When cooling your resin, you must preheat your
mold to ensure a proper cure.
Miscellaneous Tips For Moldmaking & Casting
Demolding Silicone & Resin.
To aid in the release of silicone rubber from your mold box
or your original, use a small amount of rubbing alcohol. The
rubbing alcohol will make the cured silicone rubber very slippery
and will help separate the silicone from the other surface. After
you remove the original, dry out the excess rubbing alcohol with
a paper towel or dry cloth. Be sure to warm and dry out the mold
completely before pouring resin into the mold to avoid the alcohol
from contaminating and effecting the resin.
You can also use rubbing alcohol to assist you in removing resin
pieces out of a silicone rubber mold. Use the same process as
mentioned above for removing your mold from the original and
the mold box.
When pouring RTV silicone moldmaking rubber against any non
silicone surface, mold release is not required. If you are pouring
RTV silicone moldmaking rubber against itself, you must use a
mold release. Use Alumilite’s Rubber to Rubber release
or smear a thin layer of Vaseline anywhere the silicone will
come in contact with the already cured RTV silicone rubber. If
no release is used the RTV silicone will bond to itself and you
will have a solid chunk of silicone. You will then have to cut
the silicone to remove your original.
Alumilite’s coloring dyes can be added to Alumilite’s
casting resins to achieve any color you desire.
The dyes should be added into the “A” side of
Alumilite’s resin for compatibility reasons. The dyes are
reactive which means they will crosslink and become part of the
cast piece. The dyes will crosslink with components on the “B” side
and that is why we recommend for shelf life reasons to add the
dye to the “A” side.
As a rule of thumb, the dyes can be added up to 5% of the weight
of the “A” side to reach a desired color. Adding
less dye will achieve a lighter color.
Alumilite casting resins can be filled with any dry filler of
your choice. Dry fillers are used to reduce the amount of resin
needed to cast a part making it more economic, add characteristics
such as weight, feel, or texture, and also to add physical properties
such as strength, heat resistance, and durability.
If your filler contains moisture your part will foam due to
the reaction with the moisture in the system. Use dry fillers
if you wish to avoid foaming in your part.
The Shelf Life of Alumilite casting resins are 1 year in a sealed
unopened container. The material will remain useable as long
as moisture does not contaminate the resin. For extended storage
periods, store in a cool dry place.
Bonding Alumilite is best when the material is still curing
shortly after demolding. The best adhesives for bonding Alumilite
are ones that promote a chemical bond. Adhesives that work include
but are not limited to: MMAs, epoxies, CAs (super glues), one
part silicones, one part urethanes, and hot melts.