How to Make a Mold for Fiberglass Using Foam
Fiberglass is a great medium to use to create a casting mold, but before you can make a mold you must have an object that you want to replicate. You can use an already existing object or create a new piece of artwork. Creating a new piece allows you to have complete creative control over your project. One of the best choices for making this initial piece is foam. Foam is easy to work with, light enough to use even for large-scale pieces and, most attractive of all, it's cheap.
Things You'll Need
- Foam crafting block
- Clay sculpting tool kit
- 2500-grit sandpaper
- air compressor (optional)
- Acrylic sealant
- Thin scrap wood
- Wood glue
- Molding clay
- Razor blade
- Disposable gloves
- Mold release wax (both liquid and paste)
- Buffing cloth
- Low viscosity resin
- Fast hardener
- Colloidal silica filler
- Graphite powder
- Large plastic cup
- Stir stick (Popsicle stick)
- Disposable glue brushes
- Coarse weave glass
- Scissors
- Half-face respirator with HEPA filter cartridges
- Rotary tool and a reinforced cut-off wheel
Instructions
-
-
1
Set the foam crafting block on a flat surface and carve it into the shape you want to mold with the clay sculpting tools.
-
2
Sand the foam sculpture and blow any remaining foam particles off with a strong breath or compressed air.
-
-
3
Cover the foam in acrylic sealant to prevent any moisture from penetrating the sculpture.
-
4
Make a "U" shape with three pieces of scrap wood. The "U" should be big enough to fit the sculpture within the center. Glue the scraps together to create a single solid structure.
-
5
Set the "U" upside down so the legs are on either side of the sculpture and the squared off end of the "U" is above. Hold it in place with molding clay. This structure is called a parting board.
-
6
Seal over any openings around the sculpture with molding clay. Cut away all excess clay with a sharp razor blade.
-
7
Put on disposable gloves and apply wax mold-release paste to the entire outside of the piece including the parting board. Wait one to three minutes for the wax to get tacky, then buff to a shine.
-
8
Repeat Step 7 least three, preferably five times to make sure that the coats of paste have covered the entire outside of the sculpture. Drip liquid wax release into any areas that you are having trouble getting your fingers into.
-
9
Mix equal parts of low-viscosity resin and fast hardener in a large plastic cup. Add 1 teaspoon of graphite powder and then add colloidal silica filler until the mix is about the thickness of ketchup. This creates a slow-curing epoxy.
-
10
Brush the mixture over the sculpture and parting board until it is completely covered.
-
11
Mix in three teaspoons of colloidal silica filler and spread a second layer of the mix over the sculpture.
-
12
Cover the surface of the epoxy-covered sculpture with strips of coarse-weave fiberglass. Press down on the glass to make sure it follows the contours of the sculpture as this will be the part of the mold that retains its rigidity. For small spaces cut pieces of the glass weave to give it more flexibility. Let this dry for 30 minutes.
-
13
Mix a new batch of epoxy in the same manner as before and apply it over the glass weave. Place a second layer of coarse weave glass over this layer of epoxy. Let this sit overnight.
-
14
Pull the mold apart and remove the sculpture and parting board. Don the respirator. Trim off any jagged edges of the mold with a rotary tool equipped with a cut-off wheel. Your mold is now complete.
-
1
Tips & Warnings
For larger pieces you may need to use more layers of coarse-woven glass.
Always wear a respirator when cutting fiberglass.
