HOW TO MAKE HOLLOW PRODUCTS BY
SLUSH CASTING PLASTIC RESINS
Hollow cast plastic resin allows lighter weight
castings and saves material costs.
By slush casting plastic resins you
• Make hollow, lighter weight products.
• Reduce the amount of expensive
plastic resin that you use.
• Reduce the amount of expensive
fillers that you use.
• Achieve many different “looks”, such
as metal, wood, marble, granite, etc.
The "cold cast bronze" effect
The "wood resin" effect with some
casting with plastic resin is very similar to slush
casting with plaster, so you may want to read the
previous section on slush
casting with plaster. The principal is the same -
you build up thin layers of the casting material against
the inside walls of the mold until you get the thickness
you want. With plastic resin, two or three coats of
resin are usually applied, one right after another. The
finished casting is hollow and can be very lightweight.
Or you can fill the interior with an inexpensive
material like plaster to give the casting more weight.
should use a rubber mold for slush casting plastic
resins. The cured plastic resin will be hard and rigid,
so you want to use a flexible mold. Be sure and use the
proper release agent on the rubber mold so that the
plastic resin does not stick to the mold. The companies
that provide your plastic resin and/or the companies
that provide your moldmaking material should be able to
recommend the best release agents.
plaster, most plastic resins will not "stay put" against
the walls of the mold or the previous coat of resin. As
soon as you stop rotating the mold, the plastic resin
will run off, leaving only a very thin coat behind. For
this reason, a quick setting resin such as polyurethane
plastic, or "5 minute epoxy", is normally used for slush
casting. You must keep rotating the mold until the resin
gels. As soon as the resin gels, you can prepare another
batch of resin and give the mold another coat.
advantage to using plastic resins is that you can put
various types of decorative fillers in the first coat of
resin. The first coat of resin will form the outside of
the finished casting, and will normally be the only part
of the casting that people see. You do not need to use
filler in the second or third coats of resin, since no
one would see the effect anyway. This can save a lot of
money in materials, since some fillers, especially metal
powders, are very expensive.
powder is one of the most popular types of filler used
in this way. The finished castings are usually referred
to as "cold cast bronze". To make cold cast bronze, mix
your plastic resin, then add as much bronze powder to
the resin as you can, while still keeping the mixture
thin enough to flow. A consistency a little more liquid
than honey is about right. Use this mixture of bronze
powder in resin as your first slush cast in your mold.
Tip, turn, and rotate the mold until all surfaces are
coated with the bronze-filled resin, and keep rotating
the mold until the resin gels and does not flow anymore.
m ake one or two more slush casts with plain unfilled
resin inside the first slush cast.
all the resin has cured, remove the casting from the
mold. At this point the casting will look dull and
lifeless. You won't be able to see the bronze because it
is covered over by a thin layer of plastic. Take some
very fine steel wool and rub over the entire surface of
the casting. This removes a thin layer of plastic and
reveals the bronze underneath. When you are satisfied
with the look, dust off the casting completely, and
apply a coat of spray sealer such as "Krylon" clear
acrylic to protect and preserve the finish.
marble" is also very popular, and the slush casting
technique can enhance the "marbled" look greatly. The
basic filler to make cultured marble is calcium
carbonate, also known as "marble dust". Make two or
three batches of cultured marble resin, but with a
different color pigment in each batch, such as white,
gray, and pink. Then put all the batches of resin into
the mold at the same time to make the first slush cast.
The colors will mix together and streak in unpredictable
ways while you rotate the mold, similar to the coloring
in real marble.
you need a way to make many slush castings to produce
some sort of commercial product, there are machines
available called "rotational casting" machines. These
machines work by automatically rotating the mold while
the resin gels. Using a machine also allows you to use a
plastic resin (such as polyester resin) that doesn't set
quickly, but is less expensive than the resins that do
a PDF source list
Includes 26 suppliers of all mold making and
casting materials mentioned in ALL the demonstrations on
this web site, including silicone rubber, polyurethane
rubber, latex rubber, polyurethane plastic, epoxy resin,
polyester resin, molding clay, foam board, release
agents, pottery plaster, Hydrocal, metal powders, other
plastic resin fillers, and gelatin molding compound.
With company names, addresses, phone numbers, and web
sites. Downloads to your computer as a PDF file.