How To Make Fiberglass Part - Part 2

How to Make a Fiberglass Part from a Mold

Creating a fiberglass part from a mold requires careful preparation, application of materials, and attention to detail. This guide outlines the steps needed to ensure a successful fiberglass casting, from mold preparation to final part removal.

Safety Precautions

Before beginning, always follow these safety guidelines:

• Wear skin and eye protection when working with resins.

• Work in a well-ventilated area away from open flames.

• Use breathing protection if required.

Step 1: Inspect and Prepare the Mold

1. Check for Defects: Inspect the mold for air pockets or bubbles that could affect the final part. If making multiple parts, repair these imperfections with gel coat, sand, and buff them.

2. Apply Mold Release:

   • Use Part-All paste wax to wax the mold as you would a car.

   • Allow the wax to dry for 1–2 minutes before removing it with a soft cloth.

   • Repeat this process at least three times, waiting 1–2 hours between coats.

Step 2: Prepare the Fabric

1. Pre-Cut Fabric:

   • Matte fabric can be torn into properly sized pieces as needed.

   • Modified twill fabric should be pre-cut to match the mold’s shape.

2. Position the Fabric:

   • Drape the cloth over the mold and smooth it out.

   • Make necessary cuts to ensure the fabric lays flat.

   • Mark the fabric for orientation during application.

Step 3: Apply PVA Mold Release

1. Spray a Light Film:

   • Use a Preval sprayer to apply a light film of PVA mold release.

   • Allow it to dry completely before proceeding.

Step 4: Apply Gel Coat

1. Choose Gel Coat Color:

   • Use white gel coat or mix a pigment with neutral gel coat for color customization.

2. Catalyze and Stir:

   • Follow manufacturer instructions for catalyst ratios.

   • Stir well to ensure proper curing.

3. Apply Gel Coat:

   • Pour the gel coat into the mold and rotate it to distribute evenly.

   • Avoid getting gel coat on the flange.

   • Use a brush to control the flow and remove excess.

   • Vibrate the mold to eliminate air bubbles.

4. Curing Time:

   • Allow the gel coat to cure for 45 minutes to a few hours, depending on temperature and catalyst ratio.

Step 5: Apply Resin and Fabric

1. Choose the Right Resin:

   • Use Bond Coat Laminating Resin for its long working time and cost-effectiveness.

2. Prepare the Work Area:

   • Lay a plastic bag or disposable surface near the mold.

3. Apply Mat Fabric:

   • Mix the resin according to directions.

   • Wet out mat pieces on the work surface.

   • Apply them in an overlapping pattern, ensuring full coverage.

   • Extend fabric past the mold edges but avoid bending it over.

4. Eliminate Air Bubbles:

   • Use a dabbing motion with a brush (not strokes).

   • Small disposable rollers work well for this step.

5. Apply Modified Twill Fabric:

   • Lay fabric dry to absorb excess resin from the mat.

   • If needed, wet out the fabric before applying.

6. For Extra Strength:

   • Add additional layers of reinforcement.

   • Use a surface-curing agent in the final layer for a tack-free cure.

Step 6: Trim and Cure

1. Check the Curing Stage:

   • Check the resin every 15 minutes.

   • Wait until it reaches a leathery stage (firm but slightly flexible).

2. Trim Excess Material:

   • Use a sharp razor knife to cut excess material.

   • If done too early, fabric may shred; if too late, grinding may be needed.

3. Allow Full Cure:

   • Let the part cure completely before removal.

Step 7: Remove the Part from the Mold

1. Break the Bond:

   • Use a plastic or wood wedge to loosen edges.

   • Avoid metal tools that may scratch the part or mold.

2. Pop the Part Out:

   • Apply slight leverage until the part releases from the mold.

3. Wash Off PVA Residue:

   • Use water to remove any remaining green PVA mold release.

Final Tip

Before working on a large or critical project, experiment on a small scale to familiarize yourself with material behavior and techniques.

By following these steps, you can successfully create a strong and well-finished fiberglass part from a mold.