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How To Make A
Silicone Mold
Safety and Precautions:
Please refer to the Material Sheet which accompanied your
shipment. All products should be used with good ventilation. Skin and
eye contact, ingestion and breathing of dusts and vapors should be
avoided. It is recommended you use gloves, dust masks, and eye
protection.
Types of RTV Silicone Molds:
Practice makes perfect! For first time
mold makers, we recommend you make a small mold for practice before
attempting to mold a valuable piece.
There are
four common types of molds ("Silicone Mold Types
and How To Make A Silicone Mold"):
- Block mold: one
piece with no negative drafts of undercuts. This is probably the easiest
mold to produce. The original part should be placed in the box so the
silicone is able to flow around it. If the part is simple, it can be
placed in a plastic cup, a disposable plastic container or a wooden box
(pine wood not recommended). If you choose a wooden box make sure to
seal it properly if it appears to be porous.
- Block mold-multiple piece:
This can be made exactly like a block mold and simply cut in half once
it cures to remove the part. If you prefer not to cut the mold,
partially fill the container and allow it to cure. Then apply a thin
layer of release agent, and finish pouring the mold. When the second
layer is cured, the mold should easily separate.
- Glove mold-brushed onto the
pattern: This requires a thixotropic agent which allows the
silicone to be brushed on an original piece without running off the
surface. The thixotropic agent can be supplied in the catalyst or as a
separate additive. This type of silicone is ideal for building
restoration. The silicone can be bushed on an original piece of crown
molding, allowed to cure and then be removed. The mold can then be taken
back to the mold shop where parts can be cast to produce replications of
the original molding. This type of molding is also becoming popular to
cast rocks or stones to create molds of fake rocks, rock climbing walls,
side walks and props for theme parks.
Silicone
Moldmaking Instructions!
- Cast Glove mold:
This is made by creating a void around the original part in a consistent
thickness. It is usually done by forming modeling clay around the
pattern and then forming a hard shell around the clay. The shell can be
made by using fiberglass, urethane or plaster. After the shell has
cured, the clay is removed; creating a void which can be filled by
silicone.
Supplies needed:
include gloves, mixing containers,
stirring sticks, a gram scale and a mold box.
There are several web sites which can explain how to build an actual
mold box. A brief summary of common mold boxes is listed in the section
entitled “Types of molds”.
Determine your Chemistry: There
are 2 types of moldmaking silicone materials.
Be aware of which system is best suited to your
application
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Basic
Information |
| |
CONDENSATION |
PLATINUM |
| Mix Ratio
|
10.1 |
10.1
|
| Pot Life & Demold Time |
Varies
depending on Catalyst
Not heat accelerated |
Room
temperature
or can be heat |
| Risk of Inhibition |
Not
likely |
YES
|
| Shrinkage |
Less
than .03% |
Less
than .01% / Nil |
| Durometer |
7 - 40 |
30 to
70 |
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Preparing
the Model:
Porous surfaces, such as wood, should
be dried and sealed. A clear acrylic spray lacquer is an acceptable
sealer. Also applying a release agent, such as petroleum jelly will aid
in easy release of a silicone mold. Because silicone can sometimes bond
to surfaces which contain silica, such as glass, cements and natural
stone; it is recommended to do a spot test for possible adhesion.
Mixing and
Curing:
Stirring individual components before
use is recommended. Make sure to weigh and measure accurately. Close
containers tightly after use. Products should be stored in their
original, sealed containers in an environment that does not exceed 90F.
Under these conditions, the product will achieve the expected shelf
life. Please refer to the individual products technical sheet to
determine the products expected shelf life.
The following procedure is an example of
a 10:1 mix ratio addition cure product. Please refer to the product’s
technical sheet for mix ratio information:
- Mixing: Charge 100
parts by weight of “Part A” and 10 parts by weight of “Part B” into a
clean, compatible metal or plastic container. The volume of the
container should be 3-4 times the volume of the material to be mixed.
This allows for expansion of the siloxane material as it de-gasses.
Mix thoroughly by hand or with mixing
equipment while minimizing air entrapment until a homogeneous mixture is
obtained. This will occur when the material takes on a uniform color
with no visible striations. Scrape the sides and bottom of the container
thoroughly several times while mixing. Once mixing * is complete it is
recommended that the material be de-aired 2-3 times by intermittent
evacuation for a few minutes to minimize any imperfections due to
bubbles in the cured material. Typically after releasing the vacuum 2-3
times the mass will collapse on itself at which time the vacuum should
be left on only 2-4 minutes longer
*Dispensing machine mixed material does
not normally need to be de-aired.
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Pouring the Mold:
To pour the mold, begin by pouring a
stream of silicone into one corner of the mold box. Allow the liquid to
push the air out ahead of it to avoid inducing air into the mold. If you
have a highly detailed mold, some moldmakers recommend applying mixed
silicones directly onto the detailed area and applying low pressure air
before pouring the remainder of the mold. |
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Demolding:
Please refer to the recommend time to
demold on the technical sheet for the individual products. Remember to
carefully demold at this point, since the mold has not yet achieved a
full cure.
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Storing the Mold:
It is best for the mold if it can be stored
in the original mold box or on a surface that will stress them
the least. If left in a distorted shape for extended periods of
time, the mold may not be able to return to the original state.
Keep of out sunlight and in a cool, dry area if possible |
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