CONSTRUCTING A SIMPLE MOULD BOX

General Overview

The purpose of a mold box is to contain the liquid rubber (after it is poured over and around a model) until the liquid turns to a solid.  A mould box does not have to be a complex structure – depending on the size and configuration of your model, often a coffee can, cake pan or plastic bucket will suffice.   If you make moulds of flat – two dimensional models on a regular basis and require a mold box there are a number of advantages in constructing your own mould box.

Advantages of Constructing A Mould Box 

• Easy To Construct
  
• Minimal Assembly Required
• Reusable
• Adjustable (to adapt to different size models)

Materials Needed

Original Model Used In This Presentation:  Terra Cotta Cameo Decorative Plate.
Dimensions:  15” long  x  10.5” wide  x  1” tall  (38 cm x 27 cm x 2.5 cm)

Flat Baseboard: (Plywood or Acrylic Sheeting) Dimensions - 20” long x 16” wide  x  ½ “ thick  (51 cm x 41 cm 1.3 cm)

Retaining Pieces:
(4)  2” x 3”   (5 cm  x  7.6 cm pieces of wood or acrylic)              
(4)  2” x 22” (5 cm x 56 cm pieces of wood or acrylic)

Screws:
1” (2.5 cm)

Clamps

Silicone Caulk,
Modeling clay or hot melt glue gun, 5 minute epoxy adhesive 142

Assembly

Step 1

Cut and Assemble Retaining Walls

To accommodate our model, we have constructed retaining walls out of  ½” (1.3 cm) thick acrylic strips.  We selected acrylic because most mould rubbers release easily from acrylic.  Wood can also be used.  Four pieces measuring 2” x 3” (5 cm x 7.6 cm) were cut for the shorter side of the retaining wall and four 2” x 22” (5 cm x 56 cm) pieces were cut for the longer side of the retaining wall.  These pieces were then assembled together in an “L” shape with    1” (2.5 cm) screws.  (Figure One).

Step 2

The baseboard should be at least twice the size of the original model to allow enough “working space”.   Secure the model to the backboard by applying a bead of silicone caulk or hot melt glue around the perimeter of the reverse side of the model.  Press model firmly onto baseboard and create a tight seal where the model meets the baseboard.  This will prevent liquid rubber from leaking underneath the model.

Step 3

Assemble Retaining Walls Around Model

Place retaining pieces around the model, making certain there is at least a  ½” (1.3 cm) clearance (gap) between the cameo and retaining wall.  This ½” (1.3 cm) gap will equal the wall thickness of the cured rubber mold. (Figure Two)

Step 4

Fasten the retaining walls together with C-clamps and apply silicone caulk to any seams where the liquid rubber may leak out.  This includes seams where the retaining walls meet the baseboard and also where retaining walls meet one another.  Important:  Mold box seams not properly sealed will result in rubber leakage — which equals lost time, dollars and material.  (Figure Three)

Step 5

Apply Sealer To Model ( Shellac or water based sealer undercoat )

Being made of terra cotta, the cameo and any other porous model must be sealed.  Models made of water/sulfur based clays must also be sealed as well.  Apply 2 coats of Sealer to entire model and surrounding forms  

Step 6

Apply Release Agent   ( Pol-ease   2300 or 255a )

For easiest release, apply Release agent after  sealer is dry.  Spray a light mist coating over surface of model and surrounding forms.  Brush over surface and into areas of detail.  Follow with another light mist coating and let dry for 15 minutes before applying rubber.

Step 7

Mix and pour mold rubber onto model and let cure.  Be certain that the liquid rubber levels off at least ½” (1.3 cm) above the highest point on the model.  Let rubber cure overnight.

Step 8

Removal of Retaining Walls

Finally, after rubber has cured, remove the retaining walls away from the cured mold and flex rubber mold to remove original model.  (Figure Four)

Step 9

 Remove cameo from the cured rubber.