| Safety
Read and understand the Material Safety Data Sheet (MSDS),
label and Technical Bulletin. All Polytek products can
be used safely if simple precautions are taken as recommended
in these sources of information which are provided with every
product. All products should be used with good ventilation.
Skin and eye contact, ingestion and breathing of dusts and
vapors should be avoided.
Use necessary
or recommended equipment such as gloves, dust masks, eye
protection, closed shoes, adequate clothing and (rarely)
respirators equipped with cartridges for organic vapors.
Follow directions.
All too often, projects are spoiled because in enthusiasm
for completing a project, important directions were not followed.
Please read all instructions thoroughly and call if you have
any questions, before starting your project.
Uncured Polytek
compounds may cause skin or respiratory irritation or sensitization
if improperly handled. Avoid skin and eye contact with
uncured material. If skin contact occurs, remove with waterless
hand cleaner or alcohol, then soap and water. In case of eye
contamination, flood with plenty of water and call physician.
Use only with adequate ventilation such as a large open room
with air movement. If there is any doubt about adequacy of
ventilation, a respirator with cartridges for organic vapors
should be used. Polytek products are not to be used where
food or prolonged body contact may occur.
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Physical
Properties Nomenclature
The following terms describe important characteristics of
the products.
Viscosity describes whether a liquid is thick or thin.
It is reported in centipoises (cps.). Water is low viscosity
with a viscosity of 1 cps., pancake syrup is higher - 1000
cps., while honey may be 10,000 cps., depending on temperature
of course. Temperature affects the viscosity of most of our
products. Low temperatures cause higher viscosities. For best
flow into detail, we want our materials to be warm, at least
room temperature so the viscosity is low.
Rheology
is how a liquid flows. A liquid is Newtonian if it flows and
levels even if moving very slowly. Pourable mold compounds
should be Newtonian. Brush-on mold compounds may be thixotropic,
that is they flow when brushed or troweled, but as they move
more slowly they become static and stay where they are placed.
Pour time, working
time, pot life or gel time give the user an idea how much
time they will have to work with a material from the time
mixing begins until it gels. Most materials should be in place
well before the end of this time to allow good flow into detail
and air bubbles to rise and break.
Demold time
is the soonest a curing product can be removed from the mold
if curing has been at recommended temperature. Generally,
longer time in a mold improves chances of obtaining a distortion
free piece.
Cure time
is often longer than demold time, sometimes even though a
product feels cured and can be demolded, curing may continue
for up to a week.
Shrinkage
is a reduction in size which can occur with some resins during
cure or with some rubbers after prolonged use. Casting materials
draw oil-like materials out of the rubber causing it to shrink.
Most Polytek products that stay cool during cure do not shrink
while curing.
Products that develop heat during cure may gel while warm
and as with nearly all materials, shrink as they cool, thus
the amount of shrinkage in this case depends on the temperature
reached during cure. Some resins get warmer in the center
than against the cool mold surface and tend to cause the still
liquid resin against the mold to sink. This can be corrected
by using warm molds or resins that develop less heat during
cure in the mass you are casting.
Density
is the weight of material that fills a given space. Water
has a density of 1.00 and a pound of water takes up 27.5 cubic
inches. Thus a pound of material with a density of 2 will
only fill half the space or 13.75 cubic inches. When buying
mold rubber or casting resin you must consider the price per
volume, as the price per pound can be misleading. If the product
is dense a pound will not fill as much space as a pound of
lighter material and molding and casting materials are usually
used to fill a space!
Hardness
is measured with an instrument called a Durometer. It pushes
a needle-like probe into the rubber as it is pressed against
the specimen to be tested. The farther the needle penetrates
into the specimen the lower the reading. The Shore A scale
is used for rubbers and a Shore D scale is used for plastics.
Both scales go from 0 to 100. A rubber with a Shore A hardness
of 0 is about as hard as warm chewing gum. Shore A-10 to 20
is about as soft as any mold rubbers can be. Shore A-50 is
about as hard as a car tire and above Shore A-80, rubbers
begin to feel more like a plastic, which may measure on the
low end of the Shore D scale. Shore D-90 is about as hard
as plastics get.
Tensile strength
is the force required to break a piece of material when pulled.
It is reported in pounds required to break a one inch square
specimen of material.
Elongation,
reported in percent, is the length the material stretches
before breaking.
Tear strength
is reported as the force needed to tear a split one inch long
in a piece of material. Some mold rubbers, particularly silicones,
tend to tear very easily if a split is started.
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Model
Preparation
Porous surfaces such as wood, terra cotta or plaster must
be sealed to prevent rubber or resin from penetrating the
pores. Several coats of paste wax, allowed to dry and polished
or melted paraffin, petroleum jelly, lacquer, shellac, paint,
PVA (polyvinyl alcohol solution), and potters soap on plaster
all work well for certain surfaces and mold rubber or resin
combinations. Some rubbers (Poly-Fast 72-40 and Poly Sulfides)
contain materials that will dissolve or soften lacquer and
paints. For them, wax or shellac are often used as sealers.
Poly Urethane rubbers bond tenaciously to shellac however,
so if shellac is used as the sealer, release agent must be
very carefully applied over it.
Bare plaster
is best sealed with potters soap (Murphy's Oil Soap also
works well) lathered into the damp surface of the plaster
with a soft brush, rinsed and repeated several times, then
polished with a soft brush or cloth. Soap is only to be used
on plaster, it is not suitable for sealing any other material.
If the plaster is dry, it should be wet for several seconds
under running water prior to soaping.
Moist water
clay is another special case. It can be sealed and released
by using Pol-Ease® 2350 or by spraying on a 10% solution
of petroleum jelly in mineral spirits, made by warming and
melting the petroleum jelly and stirring in the mineral spirits,
then applied using a plant spray type bottle, and allowing
the mineral spirits to dry. This prepares the water clay for
pouring of most mold rubbers. If the water clay is completely
dry, it should be sealed and coated with release as for terra
cotta.
Release agent
like Pol-Ease® 2300 must be applied to nearly every surface
before applying or pouring liquid rubber or resin. It should
be sprayed evenly and then gently brushed out with a dry brush
to pick up any excess and to spread the release over any spots
missed by the spray. The brush should be wiped with a paper
towel periodically to prevent too heavy a coating being left
on the surface. Too much release can cause pinhole defects
in the surface of the liquid material poured against it. The
coating of release should be allowed to dry for about fifteen
minutes prior to pouring. Silicone-based release agents like
Pol-Ease® 2300 may interfere with the cure of silicone
mold materials. When pouring silicones, Pol-Ease® 2350
should be used as a release on surfaces that the liquid silicone
will contact.
In every case
where there is any question about the compatibility between
the rubber and the prepared model surface, a test cure should
be made on an identical surface to determine that complete
curing and good release is obtained. Some materials such
as sulfur-containing plasticenes and wood knots, inhibit curing
of some rubbers and resins.
Porous models
must be vented from beneath to prevent trapped air from
forming bubbles in the rubber. A hole at least 1/4 inch diameter
should be drilled through the base board into the porous model.
Of course, the base of the model must be sealed around the
perimeter with plasticene or glue to prevent liquid from leaking
out under the model and through the vent hole.
Side boards
or shells should be securely fastened and sealed to the base
to prevent leakage and all side boards and shell interiors
should be well sealed and released. Petroleum jelly is excellent
for most non-critical surfaces like these, unless the material
gets warm enough during cure to melt the petroleum jelly.
Pol-Ease® 2300 is more heat resistant, but is not self-sealing,
so surfaces beneath must be well sealed.
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Mixing
& Curing
Have all materials at the same temperature. Warm room
temperature, 70-85oF, is best. Remember, it may
take 24 hours for a five gallon pail of material to warm up
to room temperature in the winter.
Have all materials
and equipment clean and ready. You do not want to have
to go searching for something after you have already mixed
the material because time is critical to obtaining good results.
Stir individual
components before use if recommended. Some materials separate
and will not cure properly if separated material is used.
Weigh and measure
accurately. Weighing on an accurate scale is best. Only
materials with a mix ratio of one to one by volume can be
measured by volume. We do not recommend trying to measure
any other mix ratio by volume.
Close containers
tightly after use. While most materials are usable at
least six months to a year after shipment if unopened, components
of polyurethanes, epoxys and some silicones can absorb atmospheric
moisture, thus should be used up as soon as possible after
the container is opened. Leaving caps off will cause deterioration
even faster, sometimes within a few days. Poly Purge
is a dry gas that can be sprayed into open containers of Polytek
Liquids before resealing to extend shelf life of these products.
See Polytek Accessories.
Time your actions
with a clock. Start timing when you start mixing. Try to have
material poured and in place before half of the working time
has elapsed so there is plenty of time for bubbles to rise
away from the mold surface.
Mix well, but avoid whipping air into the mix. Scrape
the sides and bottom of the mixing container thoroughly several
times while mixing. A Poly Paddle is invaluable for good mixing.
Sometimes, to insure that no unmixed material is clinging
to the sides or bottom, the mix can be poured into another
clean container and mixed again for a minute or two before
pouring. For large mixes, over thirty pounds, a Jiffy Mixer
on a variable speed drill may be helpful, but care must be
taken not to whip air into the mix and a mechanical mixer
does not scrape the sides and bottom of the container as well
as a Poly Paddle.
Avoid being
rushed. Careful planning should allow a deliberate pace
without mistakes.
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Pouring
The Mold
Avoid air entrapment. Most molds can be poured by simply
pouring in a steady stream into one corner of the mold box,
allowing the liquid to flow over the surface pushing air out
ahead of it. In some cases, where there is exceptionally fine
detail, some moldmakers feel that applying a small amount
of mixed rubber or resin to the surface and brushing or blowing
it into the detail with low pressure air before pouring the
bulk of the mix helps to assure that the liquid pushes all
the air out of the crevices. Caution must be taken that brushing
does not actually push the liquid through the film of release
agent on the surface, causing sticking, or that release does
not float to the top of the brushed liquid, preventing adhesion
between the poured material and the brushed material.
If a super smooth back is desired, a light spray of Pol-Ease®
2300 on the top surface of the liquid just before it gels
will help most of the surface bubbles to break.
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Curing
The Mold Or Casting
Cure at the same warm temperature that all your materials
were when mixed. Temperatures below about 65oF
will lengthen the time required for proper curing and may
spoil the cure of some materials. Placing the poured mold
or casting in a warmer area than the materials were when they
were poured, can cause problems because changing temperatures
while the material is setting can cause bubbles or distortion.
Demold carefully
as the material is still more tender than it will be a few
days later. Bending or forcing a material while it is still
only 90% cured can cause distortion that may not recover.
Obviously, the longer the material can cure before demolding
the better.
Store molds
and fresh castings properly. They can be left in the mold,
mother mold, box or on a flat surface that will stress them
the least. If rubber is left in a distorted shape for any
length of time it can take a permanent set and may never recover
to its original shape. Molds should be kept out of sunlight,
which can degrade the surface and should be kept in a cool,
dry area.
Plaster shells should be sealed on the inside with shellac
to prevent the plaster from absorbing any material from the
rubber.
Most mold rubbers will last ten or more years if properly
stored. An exception is Poly-Fast 72-40 which may degrade
after several years to an unusable liquid. Molds of this material
should be discarded before degradation becomes a problem.
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Using
The Mold
Using rubber molds with attention to the following points
will prolong mold life and produce better castings.
More rubber molds
fail due to handling mistakes than by wearing out. Proper
design and careful handling and attention to detail will prolong
mold life.
Plaster castings
will be free of bubbles if the rubber mold is wet with
Pol-Ease® Mold Rinse or with a 1% detergent (e.g. Ivory
Liquid) solution in water when the plaster is poured. Wet
the mold by dipping or spraying, do not allow to dry. Pour
the plaster on the wet surface. Please note that detergent
and soap are chemically different. Do not wet the mold with
soap, Ivory Liquid is a detergent.
Pol-Ease®
2300 is an excellent release for Poly Urethane and Epoxy resins
in Poly Urethane and Poly-Sil® silicone molds. Release
agent is not always needed in Poly-Sil® silicone molds.
Pol-Ease® 2300 should be applied as a light even spray
then carefully brushed with dry brush to pick up any excess
and cover any missed spots.
PVA is a barrier
to plasticizer and chemical migration. Poly Sulfide and
Poly-Fast 72-40 rubbers contain strong plasticizers that can
soften resin surfaces producing soft or sticky castings. If
resins must be cast in molds of these rubbers, a spray of
PVA on the rubber allowed to dry, followed by a light spray
of Pol-Ease® 2300 will often act as a barrier to the
plasticizers. PVA can be washed off the casting with soapy
water. PVA also prolongs the life of Poly Urethane molds when
casting polyester resins.
For long mold
life, avoid exposing molds to strong solvents, oils or cleaners.
All rubbers are affected by such products. Sprayed release
agents reduce solvent exposure as compared to brush application.
Store molds in their original shape undistorted, out of direct
sunlight, in a cool, dry area. Molds can be stored in their
mold shells, but porous shells such as plaster should be sealed
with shellac to prevent absorption of oils from the mold by
the plaster.
Do not allow
molds of one type of rubber to remain in contact with those
of other rubbers as migration of oils or plasticizers
from one to another can cause swelling, shrinkage, or distortion.
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Clean
Up
Paper towels for wiping up are a must. Tools should
be wiped clean before plastic or rubber is hard. Denatured
ethyl alcohol (shellac thinner), acetone or MEK are good cleaning
solvents, but are highly flammable. Work surfaces can be waxed
or coated with Pol-Ease® so hardened material can be
removed.
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