How to Design Fiberglass Mold

Fiberglass molds are used to make several copies of the same object.

Imagine being able to make a car fender, holiday ornaments or even a small swimming pool. Building a fiberglass mold of your own design can be a rewarding and challenging skill. Fiberglass is a strong, durable, and lightweight material used for making everyday items. Making your own fiberglass mold is significantly cheaper than having it professionally done. Fiberglass molds allow you to make the same item repeatedly and will last several years.

Things You'll Need

• Styrofoam
• Bondo
• Molding wax
• Sandpaper
• Polyester primer
• Resin
• Tooling gel coat
• Fiberglass mat
• Fiberglass roller
• Wooden stick
• Paint brush

Instructions

How to Create the Mold

1. Design the plug you want to use for your mold on a piece of paper.

2. Carve a Styrofoam block according to your design. Using 180-grit sandpaper, sand the foam to smooth the rough edges.

3. Cover the Styrofoam with Bondo thoroughly and allow it to dry two to three hours. Once completely dry, sand the Bondo until it is smooth.

4. Spray on the polyester primer and allow it to dry. Once it is completely dry, sand the structure using 220-grit sandpaper. Continue to sand the structure using finer sandpaper until you are wet-sanding with 1000-grit sandpaper.

5. Leave the mold to sit for three days, adding a layer of wax each day. On the third day, add three coats of tooling gel. Once the tooling gel coat has a tacky feel, you are ready to lay the fiberglass.

6. Brush resin into the mold. Separate the fiberglass strands in the fiberglass mat and lay on top of the resin.

7. Run the roller over the fiberglass to smooth out the surface and eliminate any air bubbles.

8. Soak additional fiberglass in resin, and add a minimum of three layers of fiberglass to the structure. Allow the fiberglass to dry.

9. Run a razor blade across the surface to remove any fiberglass overhang. Use the wooden stick to remove the fiberglass object from the mold.

Tips & Warnings

• Use a blow dryer between the mold and fiberglass to remove the fiberglass faster.

• The chemicals used in this project can be harmful. Make sure to use gloves, eye protection, particle mask, and a long sleeve shirt at all times.

References

• Fiberglass Warehouse: Fiberglass Mold Making
• The Composite StoreL Making a Fibergalss Mold

Resources

• Eyeball John: Fiberglass Mold Making