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*** The information provided is a general guideline. The information
does not guarantee success. Any information used will be done at
the user’s risk. Fiberglass Warehouse can in no form be held
responsible for outcome of using this information. ***
Fiberglass Mold Making
Plug preparation
To make a mold, a plug is needed. A plug is the
exact shape and dimension that the final part will be. Many times,
a replica is being made of an existing part, such as a bumper for
a car or a canoe. Other times, modeling clay, wood, or sheet metal
is formed into the final shape. If the plug is porous, such as wood,
plaster, it will need to be sealed first with lacquer or resin.
The plug should be buffed and sealed with products such as TR-301
and TR-311. A coat of mold release will need to be applied. Partall
#2 is commonly used. Five coats is a good number to make sure it
is well coated, each time buffing afterwards. For security, Partall
#10, (Polyvinyl alcohol or PVA) is used. It is a plastic dissolved
in alcohol. It is sprayed (recommended) or brushed on, allowing
thirty minutes to dry. Three coats should be applied if you want
the best possible release. Spraying with a fine paint sprayer works
the best. The first coat should be a ‘mist’ coat and
the following 2 coats a bit thicker.
Gelcoat
Tooling gelcoat is used to give the mold surface
a strong, scratch resistant surface. Please see our Gelcoat Preparation
and Application page for details on how to mix and apply gelcoat.
Tooling gelcoat comes in black or orange to be able to tell the
difference between the part and mold. ***Do not use Gelcoat with
wax in it.*** Spray (recommended) a thick layer of gelcoat on the
plug. The layer should be between 15 and 20 mils. Let the layer
cure. (If the layer is not mostly cured, the styrene in the following
coat may cause it to wrinkle, also calling alligatoring.) Allow
to cure for 2 to 4 hours, or until the gelcoat can not be scratched
with your fingernail, but still tacky.
Fiberglassing
A layer of 1 oz Chopped Strand Mat should be layed
down as the first layer. General Purpose Polyester resin or ISO
Resin 75-200-319 is commonly used as the resin. The ISO resin is
a tooling resin which shrinks less than the GP resin. This may not
be a factor for most parts, but large molds or final parts with
critical dimensions should use the ISO resin. The resin should be
mixed with 1% to 2% MEKP. Wet the mat out with a brush or spreader.
Work the resin in with bristle roller. Afterwards, use a aluminum
roller to force out all the air. When you are done, there should
be no white fibers or air pockets visible. Allow the resin to cure.
When the resin is hard, but still tacky, it is time to put the next
layer on. Never cure multiple layers at one time because this may
cause warping, especially in large molds. Add additional layers
of mat and/or cloth to give the mold strength. An additional 3 layers
of 1.5 oz mat is usually sufficient, depending on the application.
Be sure to allow adequate curing time between layers.
Removing the Plug
Allow 2 or 3 days for the mold to cure completely.
Use a plastic wedge or sharpened paint stirrer (never use hard or
metal tools) to slide between the mold and plug. (If there is excess
resin or fiberglass hanging over the edge of the plug, the plug
will not be able to slide out. The excess will need to be cut off.)
Separate the entire edge of the mold from the plug. You should be
able to remove the plug from the mold.
Mold Preparation
It is time now to prepare the mold for use. Most
times, the mold will need to be sanded and polished. Sand the mold
by using 220 grit going to 600 grit. Afterwards use the TR 301 and
311 (or equivalent, Meguiars #1 and #3 will work also) to polish
and seal the mold. Wax and buff with Partall #2 and coat with Partall
#10. For the first 5 parts off the mold, use Partall #2 and Partall
#10 again. This should fully season the mold. Apply Partall #2 after
each part going forth.
List of Materials Needed
Sand Paper
TR 301 (or equivalent)
TR 311 (or equivalent)
Partall #2
Partall #10
Buffing Pad
Black or Orange Tooling Gelcoat
MEKP
1 oz Chopped Strand Mat
1.5 oz Chopped Strand Mat
Style 7500 Fiberglass Cloth (if necessary)
General Purpose Laminating Resin (or)
ISO Resin 75-200-319
Spreader or Squeegue
Bristle Roller
Aluminum Roller
Small Wedge
Stir Sticks
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