Handout for Sculptural Methods Class. This one is "moldmaking"

1. spring 2010 Clay, Metal, and Casting, Projects Class (S.J Choi ) page 1 of 7
Mold making & Casting Handout(For chemical based materials)
* MOLD MAKING PAST & NOW
People have been making molds for thousands of years, dating back to ancient Egypt and
China. Through the years, a variety of materials have been used to make molds including sand,
wax, glue, animal fat, gypsum, alginate, metal, plastic, re-usable vinyl, gelatin and others.
Still use a variety of materials, but a majority uses one of four different flexible rubber products
for the following reasons: 1) these rubbers reproduce exact detail 2) flexibility allows for easy
removal (demold) from the original model and the cast piece, 3) they generally give long life,
allowing for multiple reproductions, 4) because they generally yield many reproductions, which
also makes them cost effective. These rubber products are latex, poly-sulfides, poly-urethanes,
and silicones.
* MATERIAL ADVANTAGE AND DISADVANTAGE
The next few paragraphs review these common mold rubbers along with advantages/
disadvantages of each.
I. Latex : To make this rubber usable as a mold material, the raw rubber is usually processed
with ammonia and water. Latex is almost always brushed onto an original model (not poured).
- ADVANTAGE: Natural, One-component system, Inexpensive, Thin-walled, Strong and exhibit
good abrasion resistance.. Latex molds are also good for casting wax and gypsum.
- DISADVANTAGE: Shrinkage (10 to 20%), Ammonia odor, Making molds with latex rubber is
slow and time consuming. Brush-on molds made with latex require as many as 20 brush coats,
with 4 hours of drying time between each coat. (* new latex products on the market with lower
shrinkage and no odor). Latex molds are generally not suitable for casting resins.
II. Poly-sulfide rubbers : Two-component systems (base plus curative; A+B), Available for
making molds that are poured or brushed on.
- ADVANTAGE : Soft, "stretchy" and long lasting (over 40 years), Good for making molds with
severe undercuts,fine detail. Not inhibited by sulfur or water based modeling clays, Minimal
model preparation. Good for casting wax (lost wax process) and gypsum plasters.
- DISADVANTAGE: Mostly offensive odor. Newly made poly-sulfide molds may stain plaster.
Poor abrasion resistance (not good for casting concrete, production casting of resins. Accurate
mix(A,B part system) by weight (scale required), Moderate cost; higher than latex and urethanes
but lower than silicones.
III. Silicone rubbers : Two-component systems (base plus curative; A+B), Available in a
hardness range of very soft to medium. Cured with either a platinum catalyst or a tin catalyst.
Available for pouring, brushing or spraying types.

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- ADVANTAGE : Best release properties of all the mold rubbers. Good for production casting of
resins (poly-urethanes, polyesters and epoxy). No release agent is required. No post-production
cleanup. Good chemical resistance and high temperature resistance (400°F / 205°C and
higher). Only suitable for casting low melt metal alloys (i.e. tin, pewter, lead).
- DISADVANTAGE: High cost . Sensitive to substances (sulfur clay for example). Thick (high
viscosity), Lot bubble.(* Using brush-on rubber mold, the time factor between coats is long
(longer than urethanes or poly-sulfides, shorter than latex). Accurate mix(A,B part system) by
weight (scale required). Shrinkage. No long library life.
IV. Polyurethane rubbers : Two-component systems (base plus curative; A+B), Low cost.
Available for pouring, brushing or spraying types.
- ADVANTAGE : Easy to use, Simple mix ratio by volume (i.e. 1A: 1B) - No scale required. Wide
hardness range. Low viscosity. No vacuum for bubble. Good abrasion resistance. Less expen-
sive than silicones and poly-sulfides.
- DISADVANTAGE: Worst release properties, Very adhere to anything. Need good model prepa-
ration ,Moisture sensitive, May bubble if exposed to moisture (working on humid day, for exam-
ple). Limited shelf life (effect from ambient moisture in the air.)
* PROCESS
Whether you choose a silicone, polyurethane or poly-sulfide, read the technical bulletin for that
product. Every technical bulletin has important information about that specific product's use
(most common applications), technical information (mix ratio, Shore hardness, viscosity, cured
strength, etc.), and much more. There is also information about safety, general mold making
techniques and how to get the most out of your cured mold.
These materials are safe if used properly and as directed. Follow these general safety
tips:
* Mold making and casting is not for children. Keep all materials out of the reach of children.
* Good ventilation is essential.
* Wearing rubber gloves and long-sleeve garments will help minimize skin contact. Uncured
rubber can be removed from working surfaces with WD-40,acetone,etc.
* Be aware of your temperature. The workshop and all materials (including your mold) should be
maintained at, or near, room temperature (77° F / 25°C). The colder the environment, the longer
mold rubber will take to cure and if the temperature is too cold, (50°F / 10°C), the rubber will not
cure at all. Warmer environments will reduce the amount of time you will have to mix and pour
or brush on rubber.
* Humidity should also be kept at a minimum. High humidity will react with polyurethane mold
rubbers .

3. page 3 of 7
* Working surfaces should be accessible from at least two sides and should be level in all direc-
tions. To protect the surface from spills and stains, cover the tabletop with news paper or brown
wrapping paper. Also, wear "disposable" clothing. These materials will permanently stain cloth-
ing.
* Don't risk a valuable model. . . Test the material in question on a similar surface before apply-
ing to the model(especially, between the mold rubber (sealer, release agent, etc.) and the model
surface
* Materials Needed For Making Mold and Casting
• Disposable clear containers
• News paper or Brown paper
• Modeling clay
• Mixing containers/Measuring Containers
• Mixing Sticks/ knifes
• Sealing agent
• Release agent
• Coddles
• Clamps(vinyl and latex)
• Cheap brushes
• Rubber band
• Glue gun
* Making A Flat-Back One-Piece Block Mold
Step 1: Start With a Model - Models can be made of virtually any material: wax, clay, plaster,
stone, concrete, paper, metal, bone, fabric, etc.
Step 2: Build a Containment Field - The purpose of a containment field is to prevent the liquid
rubber from leaking out the sides or bottom and contain it until the liquid turns to a solid, flexible
cures. The containment field can be something as simple as a paint can, cigar box, cake pan,
coffee can, etc. Or construct a " mold box."
For molding irregularly-shaped molds, the baseboard can be cut to the desired con-tour. Use
light gauge sheet metal, linoleum or cardboard for the side wall. Overlap and tape pieces to-
gether. Hold in position with cord and wedges.
Step 3: Secure the Model - Using silicone caulk, a glue gun, Instant epoxy, or clay, you must
secure the model to the baseboard. We have rolled modeling clay into thin beads and pressed
the clay around the back perimeter of the model. We then center the model in the mold box and
press firmly on the piece in all directions. This flattens the clay and creates a tight seal under the
model to prevent rubber from leaking underneath. You can also nail or screw the model to the
baseboard, but this damages the model. If the model is highly porous, it should be vented from
underneath to prevent trapped air from forcing bubbles in the rubber.

4. page 4 of 7
Step 4: Seal the Seams - To prevent the liquid rubber from leaking out the sides or bottom of
the mold box, all seams are sealed. You can use silicone caulk, a glue gun, Instant epoxy™ or
modeling clay. (Remember, if using silicone rubber for your mold, do not use silicone caulk.)
Step 5: Apply Sealing Agent - Models made of porous materials (plaster, stone, concrete, wood,
etc.) require a sealing agent to seal surface porosity. Clays that are water-based or sulfur-based
must also be sealed. Suitable sealers include shellac, paste wax, and petroleum jelly thinned
with mineral spirits.
Step 6: Apply Release Agent - After sealing the model's surface, applying a release agent will
allow a model to be easily released from the cured rubber. Use a release agent specifically
made for mold-making and casting. Using the wrong release agent will result in the mold rubber
sticking or bonding to your model or the mold rubber will not cure.
* Wrong Release Agents
Spray Vegetable Oil (Pam)
Mineral Oil
Petroleum Jelly
Motor Oil
Spray Lubricants (WD40)
* Right Release Agents
Universal Mold Release / Any kind of Release Products (Mann Ease Release Series)
Mold release agents come packaged in both convenient aerosol sprays or economical liquids
that can be brushed on or sprayed on using a non-aerosol sprayer.
Note: If using a silicone rubber, do not use a silicone-based release agent to release the mold
rubber from the model. It is not necessary. If releasing silicone rubber from silicone rubber (mak-
ing a two-piece block mold, for example), use special one (Mann's Ease Release™ 800 non-
silicone-based release).
* Proper Application Of The Release Agent
Warning! Failure to properly apply a release agent will result in the rubber completely sticking
to the model, or sticking in some places but not in others (spot sticking).
* The proper way to apply a release agent is to:
1) Apply a light mist coating over the entire surface of the model and surrounding forms
(any surface that will come in contact with the rubber). Do not over-apply!

5. page 5 of 7
2) Use a clean paintbrush to brush the release agent over the surface of the model and
surrounding forms. Make sure that intricate detail, undercuts and hard-to-reach areas
are coated as thoroughly as possible.
3) Apply another light mist coating and let dry for 10 minutes.
Do not soak your model with release agent. Over-applying release agent will result in
tiny bubbles on the working surface of your finished mold (pin-holing) and will be re-
flected in castings taken from the mold. Once "sealed" and "released," our model is now
prepared. The next step is to measure, mix and pour the mold rubber over our model.
* Release Agents Chart
Original ! ! Molding Compound ! ! Release Type Suggestions(#products from T.C.S)
Clay, Metal, Plastic ! Urethane Rubber! ! ! Silicone! ! UMR, 2251, 2300, 2601, 2910
Clay, Metal, Plastic RTV Silicone! ! ! Wax/Teflon! ! 500, 2310, 2831
Clay, Metal, Plastic! Urethane/Epoxy Plastic! ! Mixture! ! ! ! 200
Plaster! ! ! Urethane Rubber! ! ! Wax/Soap! ! 2310, 2831
Plaster! ! ! RTV Silicone! ! ! Wax! ! ! Sonite Seal, 2831
RTV Silicone! ! RTV Silicone! ! ! Non-Silicone! ! ! 800
Plastilina, Plaster! ! Polysulfide Rubber! ! Wax! ! ! Sonite Seal, 2831, PVA
Concrete! ! Urethane Rubber! ! ! Oil/Soap!! ! Castor Oil, In & Out
Aqua-resin! ! Silicone Rubber! ! ! None! ! ! (just use Kiril-B)
Aqua-resin! ! Alginate!! ! ! SEPR-8! ! ! ! SEPR-8
Aqua-resin! ! Latex Rubber! ! ! Parfilm, PVA! ! Polyester Parfilm, PVA

6. page 6 of 7
* Measuring Mold Rubber
As stated earlier, some mold rubbers require accurate weighing of components (A +
B). These include most silicones (Smooth-Sil series), poly-sulfides (FMC series) and
some poly-urethanes PMC series). If you are using a mold rubber that requires a scale,
use an accurate scale such as a gram scale or a triple beam balance.
* Mixing Mold Rubber
One of the most common reasons for mold rubber not properly curing is improper mixing. It is
imperative that you develop and practice a good mixing technique.
Mix Parts A + B for at least three minutes.
• Be Thorough, Not Fast! Most mold rubbers give you plenty of time to mix and apply.
• Do not whip the material or create a vortex -- this will introduce air into the mix that may result
in air bubbles on the working surface of the finished mold.
• Stir slowly and deliberately, making sure that you scrape the sides and bottom of your mixing
container several times.
When you think you have mixed the rubber enough, mix it again just to make sure.
* Pouring Mold Rubber
With the mold rubber thoroughly mixed, it is now time to pour it over our original model. Do not
pour rubber directly onto the model as this may entrap air. Instead, find the lowest point in the
mold box and pour the rubber there -- in a single spot and at a slow, constant rate. Let the rub-
ber rise up and over the model. This will displace air from the lowest point and help minimize air
entrapment.
You will notice tiny air bubbles rising and dissipating on the surface. You can further dissipate
these bubbles by lightly passing a heat source (hair dryer or heat gun) over the surface.
* Let the Rubber Cure...
The next step is easy . . . let the rubber turn from a liquid to a flexible solid (cure) overnight (16
hours) at room temperature (77°F /25°C).
* Accelerating the Cure
If you want to reduce the cure time of the rubber, you have two options:
1) Cure accelerator can be added and will reduce the cure time. Mostly added to Part B and
mixed thoroughly before adding Part A. Consult their Technical Bulletin for more information.
2) Apply Heat. Warmer temperatures will cause the rubber to cure faster.

7. page 7 of 7
* Demold
After the rubber has cured, it is time to remove our original model from the finished mold, or
"demold." If all went well . . . The rubber flexes easily and the original model should release
from the cured rubber. The mold should reflect every last bit of detail (down to a fingerprint) of
the original model.
* Casting Into A Finished Mold
There are a variety of materials that can be cast into a finished mold.
Wax - For candle-making, reproducing jewelry, and sculpture (the lost wax process).
Gypsum Plaster - For architectural restoration, reproducing sculpture.
Modified Gypsum - For making exterior or interior architectural elements, sculpture, metal cold-
casting.
Concrete - Statuary (ornamental) and architectural elements.
Modified Concrete - Exterior architectural castings, ornamental concrete, sculpture reproduc-
tions.
Urethane Resins - Reproducing sculpture, jewelry, special effects, tooling & prototyping, gen-
eral purpose interior/exterior applications, industrial parts.
Polyester Resins - Plastic castings, architectural elements, sculpture, laminations, reinforce-
ment.
Epoxy Resins - Vacuum form molds, production tooling, foundry patterns, forming dies, hard
rollers, industrial parts.
Urethane Foams - Arts & crafts, industrial uses and special effects. Straight casting, backfill-
ing, encapsulation, cushioning.
* Material Supply
- The Complete Sculpture ; On/Off line : 90 Vandam St, between Hudson St and Greenwich St/
www.sculpt.com/ 1-800-9-SCULPT
- www.smooth-on.com
- www.tekcast.com
- www.rubbermoldcompounds.com
- www.polytek.com

8. spring 2010 Clay and Casting, Projects Class (S.J Choi ) page 1 of 3
Making a Brush On Rubber Mold
The advantage of making a mold by brushing rubber onto the model is that it minimizes
the amount of rubber used, saving you material costs. Making a brush-on mold,
however, requires more time and labor vs. pouring rubber.
Brush-on rubbers come in different forms and may be mixed one-to-one by volume (ure-
thanes such as Brush-On 40t), or may require an accurate scale for weighing compo-
nents
Making A Brush-On Mold Step-By-Step
The process for making a brush-on mold is almost like making a pour-on mold.
Step 1: Build a dam(like coddles) around the model- Because of brushing on 3 Dimen-
sional model and flowing Rubber material, it needs a dam (like coddles) not to run down
during applying rubber. And it lays news paper or brown paper under the model. The
model should be accessible from all sides. A platform that rotates 360 degrees makes
brushing rubber onto the model very easy.
Step 2: Seal The Model - Some model out of clay that contains sulfur, it must be sealed
using spray shellac. Remember: Failure to seal the model may result in the mold rubber
not curing.
- Reminder: If you are using silicone rubber (such as Mold Max 30) to make your mold,
do not use shellac as a sealer. Instead use either Super Seal or acrylic spray.
Step 3: Apply A Release Agent - Universal Mold Release will make it releasing easily
and is absolutely necessary if shellac was used as the sealer.
* Proper way to apply release agent:
• Apply a light mist coating to all surface, forms and mounting platform.
• To ensure thorough coverage, use a soft brush to brush the release over the model’s
surface, into undercuts and over areas of fine detail.
• Apply a second light mist coating and let dry for 10 minutes prior to applying the mold
rubber.

9. page 2 of 3
Step 4: Measuring Mold Rubber
The mold rubber we will feature for this demonstration is “Brush-On” 40. Part A is a
liquid and Part B is a paste. When combined in equal amounts (by volume--no scale
required), Brush-On 40 self-thickens and can be applied to a vertical surface without
sagging.
Dispense the paste (Part B) into the measuring container. Using a spatula or stirring
stick, be sure to eliminate any air voids. Use a spatula to level off at the top and thor-
oughly empty contents into a mixing container.
Fill the same measuring cup to the top with the Part A liquid and empty into the the mix-
ing container. With Parts A and B now properly measured and dispensed into the mix-
ing container, proper mixing technique is used to blend the components.
Mix thoroughly for three minutes, making sure that the sides and bottom of the con-
tainer are scraped several times. Parts A + B should blend thoroughly to a uniform color
without any signs of streaking in the mix.
Step 5: Applying the Rubber
At least four layers of Brush-On 40 are necessary to build a suitable mold thickness.
Generally, 3/8”-1/2” (.95 cm - 1.3 cm) is adequate.
The first layer is generally known as the “detail coat,” and is applied thinly to the
model surface with short, dabbing strokes. Subsequent coats can be applied with more
fluid strokes and will give the mold strength and durability.
In applying the first coat, you should strive to cover every last bit of detail on the model
surface, and coat hard-to-reach areas and undercuts. In this case, care is taken to en-
sure coverage of all features, particularly the eyes, nostrils and in and around the ears.
The base is also covered.
Once the model is covered, it is allowed to dry for 30-40 minutes (at room tempera-
ture) until “tacky.” Tacky means that the rubber has started to cure and is no longer
“wet.”

10. page 3 of 3
It is sticky to the touch, but will not come off on your finger (use only a gloved hand or a
spatula to touch the rubber).
Note: Colder temperatures will prolong the cure time, while warmer temperatures will
accelerate it. Do not apply the second coat if the first coat is still wet!
Step 6 : Applying The Second Coat
When the first coat has become tacky, apply the second coat. The second coat is ap-
plied with longer, more fluid strokes and completely covers the first coat. Be care-
ful not to disturb the first coat.
After the model is covered (if you use small amount of pigment, this coat makes it easy
to determine when it is covered), the rubber is again allowed to become “tacky” prior
to applying the third coat.
Apply the third coat, unpigmented this time. Allow this coat to “tack up.”
Apply the final coat--with pigment.
Between third and final coat, attach the keys for holding the support shell on tacky
condition. It prevents for detaching rubber mold from support shell. The keys should be
used same material and can be prepared left over from first or second coat process.
After the final coat is applied, all coats are allowed to cure overnight (16 hours at
room temperature).
Step 7 : Applying The Support Shell
With the rubber fully cured and still on the model (do not demold yet!), a reinforce-
ment shell (mother mold) must be applied to the model.
Again, the purpose of the support shell is to maintain the shape of the rubber mold
when casting into it.
The support shell should be out of plaster, fiberglass, plastic, resin and some products
designed for the support shell.

11. Introduction of Fiberglass
(2010 Spring Class Demonstration)
Background
Fiberglass refers to a group of products made from individual glass fibers combined into a va-
riety of forms.
Glass fibers can be divided into two major groups according to their geometry :
1)continuous fibers used in yarns and textiles
(reinforcement material for molded and laminated plastics)
2)discontinuous (short) fibers used as batts, blankets, or boards for insulation and filtration.
(Fiberglass wool, a thick, fluffy material for thermal insulation and sound absorption)
Example : in ship and submarine bulkheads and hulls; automobile engine compartments and
body panel liners; in furnaces and air conditioning units; acoustical wall and ceiling panels;
and architectural partitions.
History : Artisans created glass strands for decorating goblets and vases during the Renais-
sance. A French physicist, Rene-Antoine Ferchault de Reaumur, produced textiles decorated
with fine glass strands in 1713, and British inventors duplicated the feat in 1822. A British silk
weaver made a glass fabric in 1842, and another inventor, Edward Libbey, exhibited a dress
woven of glass at the 1893 Columbian Exposition in Chicago.
Glass wool, a fluffy mass of discontinuous fiber in random lengths, was first produced in
Europe at the turn of the century, using a process that involved drawing fibers from rods hori-
zontally to a revolving drum. Several decades later, a spinning process was developed and
patented. Glass fiber insulating material was manufactured in Germany during World War I.
Research and development aimed at the industrial production of glass fibers progressed in the
United States in the 1930s, under the direction of two major companies, the Owens-Illinois
Glass Company and Corning Glass Works. These companies developed a fine, pliable, low-cost
glass fiber by drawing molten glass through very fine orifices. In 1938, these two companies
merged to form Owens-Corning Fiberglas Corp. Now simply known as Owens-Corning, it has
become a $3-billion-a-year company, and is a leader in the fiberglass market.
Raw Materials : The basic raw materials for fiberglass products are a variety of natural
minerals and manufactured chemicals. The major ingredients are silica sand, limestone,
and soda ash. Other ingredients may include calcined alumina, borax, feldspar, nephe-
line syenite, magnesite, and kaolin clay, among others. Silica sand is used as the glass
former, and soda ash and limestone help primarily to lower the melting temperature.
Other ingredients are used to improve certain properties, such as borax for chemical
resistance.
page 1

12. Fiber glass Forms
Fiberglass Mesh - Alkali Resistant Mesh for reinforcing casts or mother molds, reinforcing Winterstone
sculpture and setting mosaic tile. Cuts easily
(Mesh is white, the teal color in this picture is only the background for the picture.)
Fiberglass Veil. A super thin veil for reinforcing casts or mother molds. Ideal for applying to highly de-
tailed areas.
Fiberglass Mat. chopped-strand mat for reinforcing casts or mother molds.
page 2

13. A/R Fiberglass (Loose Strand)- Flexible for use in concretes, Winterstone and any alkaline base me-
dium
Fiberglass Cloth. Plain weave, 14mils thick. Use this fiberglass cloth to create high strength parts. It is
popular for lamination and high strenth casting. It is also, often used in fiberglass mold making.
AquaGlass (AQG) Chopped Strand - This fiberglass is specially design to work with Aquaresin as both
a reinforcement material and thixotropic additive. The flexibility of the fiberglass facilitates easy mixing
without and preliminary soaking. " Aquaglass is also ideal for any type of water-based application like:
plaster, hydrocal, ultracal, fgr-95, forton mg and matrix g. Not for Cement.
page 3

14. MAKING A FIBERGLASS MOLD
- The first step is to apply a gelcoat of Resin which will be the mold surface.
- The gelcoat should be in contrasting color to the surface of the part you will make. Since most
parts are light colored, black gelcoat is commonly used.
- If the gelcoat is to be brushed on, two coats must be applied, and the first coat must cure sev-
eral hours before the second coat is applied.
- When the gelcoat has cured so that it cannot be scratched off with the fingernail at the edge of
the mold, which takes from 2 to 4 hours to overnight in cool or humid weather, you are ready for
the “skin coat.”
- Between first and second coat, you can apply fiberglass mat.
- The resin should be applied with brush or a mohair roller until no white fibers remain.
- Be careful not to over-catalyze when laying up the glass. Above 75°F one 10-15 cc of hardener
to the quart will generally suffice. Below 70°F, 20 cc per quart. Do not work below 65°F.
- For a large mold, it is good to apply just one layer per day. After the “skin coat,” you can use
1! oz. mat for a faster build-up.
Generally, woven roving is not used in molds because the pattern transfers through the mold to
the gelcoat. If it is necessary to use woven roving for strength in a large mold, it is applied after
a thickness of 3 or 4 layers of mat has cured hard. The thickness required in a mold depends
upon size and shape and the number of parts to be taken off. For a dinghy mold to be used only
a few times, four layers of mat might be adequate.
page 4

15. The regulations of fiberglass operations
A number of regulations can apply to fiberglass operations. These regulations stem from the
types of products used and types of wastes generated by the industry. Table A lists typical fiber-
glass processes, products and wastes. The regulations, referenced in the table, protect worker
health and safety, community rights and the environment. (Table A -- Typical Fiberglass Processes,
Products Used and Wastes) "
- Worker Health & Safety
The state's Department of Labor and Industries implements worker health and safety regulations.
If you employ one or more people in your shop, you must ensure that:
•! Workers have access to appropriate safety and protective gear, like gloves and respirators.
•! Workers understand any hazards associated with their job. Hazardous products must be
identified and labeled, and information about the product must be kept on-site.
! •! Workers are not exposed to excessive levels of air-borne pollutants, like styrene.
- Resin -- Often Hazardous because it is flammable and contains styrene monomer.
"
- Initiators & Catalyst - Often Hazardous because they're flammable and explosive due to per-
oxide content.
Worker Safety -- Fire Risk : Local fire codes regulate flammable products, like acetone and
resins. Especially, peroxide catalysts must be stored in an explosion-proof cabinet.
Air Emissions : Fiberglass can create smog, damage the Earth's ozone layer, impact human
health and affect the environment.
Hazardous Wastes : Some fiberglassing wastes are regulated because they are hazardous. For
example, spent acetone is regulated because it is ignitable, and spent emulsifier is sometimes
regulated because it is toxic to fish.
page 5