Skin Coat (Brush On) Mold
this How To we are going to demonstrate the process of making
a brush on mold using Dow Corning’s HS II silicone rubber
and a rigid mother mold using Alumilite’s Skin Coat Rigid
for a quick and cost effective alternative to pouring block molds. We
will then show you how to make beautiful hollowed out cast replicas. Here
we are making a mold of a paper mache hand sculpted decorative
pumpkin that can be hung either indoors or outdoors.
original was made out of Ave’s Paper Mache and is hollowed
out on the back side. They are hung primarily indoors because
of the sensitive nature of the paper mache.
To over view the process, we are going to mount the original
to a board, paint a silicone mold over the original, and then
make a rigid mother mold using Alumilite's Skin Coat Rigid urethane.
Once the mold is complete, we will then be able to brush the
Skin Coat into the rubber mold to make extremely durable exact
replications of the original work of art. Here's how it will
the pumpkin to a flat board.
sure to seal the bottom edges of the pumpkin to the board. This
will make for a straighter edge and cleaner mold.
Alumilite’s UMR release, spray the mold and wood to ensure
a good release.
initial coat of our silicone rubber will be straight HS II mold
making rubber from Dow Corning. The HS II is a flexible rubber
with great tear strength.
used approximately 1.5 lbs of base and .15 lbs of catalyst to paint
on our initial skin coat. The HS II has a mix ratio of 10:1
the rubber thoroughly until absolutely no swirls are seen in the
rubber or along the sidewalls of the bucket.
thoroughly mixed, begin to paint the silicone over the master.
the silicone into the detail of the master with the brush, making
sure every bit of detail is coated with a thin layer of rubber. This
initial coat ensures the detail is picked up in the rubber mold. The
next steps are to add thixotropic additives to the following coat/s
to build thickness behind the initial thin coat which will add
durability and toughness to the paint on rubber mold.
to paint on the initial thin coat of rubber until the entire piece
and 1-2" of flange area is covered.
your next step mix up approximately double your first coat and
now add some HS II Thixotropic Additive to make the consistency
of the rubber thicker. This will enable you to paint on a
thicker layer of silicone to build up your wall thickness of your
mold. Start by adding only a few drops of the Thixotropic
Additive to the mixed silicone rubber. This will only make
the mixed rubber thicker and does NOT affect the work or cure time
of the rubber.
recommended percentage is .5% Thixotropic Additive which is difficult
to measure. Therefore start with a few drops, mix it, and
evaluate the consistency.
its not thick enough to build your wall thickness, add a few more
drops and mix it in.
this process until you achieve your desired consistency of the
rubber that will allow you to paint on and build up your silicone
rubber wall thickness.
are now ready to start painting on your build up layer/s.
sure to cover all of the surface area with at least a ¼” of
soon as you are done painting on your build up layer, place some
locators (here we used some small cut up sections of old HS II
rubber molds) on the back side so the mother mold will properly
line up with the silicone brush on mold.
the silicone cures, trim the excess flange area off with a knife. This
will make a cleaner and straighter flange for the mother mold to
some pieces, it may be difficult to remove the rigid mother mold
from the original without first peeling the silicone rubber from
the original to release the surface tension. Therefore, work
the silicone up around the edges and peel it up off of the original
on one side and then the other.
simply lay it back down into place over the original. Make
sure all sides are released. This will make the removal of
the rigid mother mold much easier.
painting on the Skin Coat to make your mother mold, spray the UMR
to allow for an easier release between the silicone brush on mold
and the rigid mother mold. You can also use Stoner Mold
Release if available.
is a good idea to seal the wood base where the Skin Coat will come
in contact with Vaseline to ensure an easy release.
equal amounts of the Skin Coat Rigid A and B side and immediately
start to mix.
15 seconds of the two parts coming in contact with one another,
the material will start to thicken. As it thickens, it is
not curing but rather building thickness to a brushable consistency.
are now ready to start brushing on the Skin Coat Rigid over the
silicone mold. Be sure to cover the entire area evenly. We
used two coats of approximately 3 lbs each to cover and complete
the mother mold. Be sure to only mix enough material that
you can work with in the 8 minute open time allowed.
until the entire part and flange area is covered.
the material cures, set and paint in a couple of wood blocks that
can be used as a stand or mounting area.
mounting blocks will help you keep the mold flat when you flip
it over and prepare to make your first reproduction.
the Skin Coat Rigid has cured, using a putty knife, pop the mold
and part off of the wood base.
you can see inside the back of the hollowed out original.
working the edge around the mold and part to release the mold from
you’ve worked the part lose, simply pull the original out
of the rubber mold. This will be fairly easy since you’ve
already peeled the silicone off of the original before painting
the Skin Coat on.
should be able to remove the original with very little damage. The
silicone will not affect the paint or any part of the original
as long as the original is not porous and does not allow the liquid
silicone to soak into the surface of the original.
brush on silicone rubber mold comes out of the mold very easily. It
lays right back into place and the silicone square chunks we put
on the back are perfect locating pins to make sure the rubber mold
and Skin Coat mother mold line up perfectly.
clean the edge of the mother mold, use a hand saw, ban saw, trimming
shears, or a sharp knife to trim the flange.
silicone brush on mold and mother mold are now ready to start producing
lease call us toll free if you have any questions
regarding your mold making or casting project. 800 447-9344