How to Build a Fiberglass Box
In many instances, the correct box or shape for a project is unavailable. If you want an exact size and color in a box, making one on your own the best way to go. Fiberglass is a good material to use for this purpose. This simple project takes a little time for the components to dry, but will yield a good-looking product precisely suited to your needs.
Required Materials
- foam
- Bondo
- fiberglass mat and strips
- paint
- resin
- resin colorant
- sandpaper 400-4000 grit
- polyethylene two-part construction grade form
Required Tools
- orbit sander
- serrated kitchen knife
- handfuls of brushes
- mixing sticks and mixing dish
- small chisel
- measuring tape
- pencil/paper
Instructions
- Layout - If your box is going to be inserted into some other space such as a dashboard, measure the space that you are going to be inserting into. Draw a plan with dimensions and in 3D if you are able.
- The Mold - Carve out the shape that you will be constructing in foam. If a box, make sure that the edges are exactly straight and at perfect degrees. This is important because no matter how careful you try to be, fiberglass seldom forms a perfect 90-degree corner. Once the basic foam shape is made, give it three coats of paint. You are painting the foam because it does not react well with Bondo; the paint acts as a barrier. Use Bondo to finish the shape using thin layers.
- Finishing the Bondo - Once the Bondo is built to the desired shape, let it dry, but not to a hard finish. Use a file to get the piece fairly close to the finished project size. Make sure it is fairly smooth. Now allow it to dry to a hard finish. Paint the Bondo with any type of paint and let that layer dry - this will let you see any imperfections. Sand the Bondo to a smooth finish.
- Applying Fiberglass - Apply the fiberglass by coating it with resin and laying it over the mold. Thinner strips work best for corners or smaller pieces, and sheets work best for longer and wider projects. Try to keep wrinkles, pits, and defects to a minimum. If a defect is left on the project, it will spread throughout the project and look bad. It will also make sanding a problem later on.
- Sanding - Sanding is where everything comes together, and it is also the stage that it is often not done well enough. When it comes to sanding a fiberglass box, there is never enough sanding to be done. Begin with a 400-grit paper on your orbit sander. Do not use other sander types as they will leave deep scratches in the final project. As you sand, make sure to keep the project clean of the sanded fiberglass waste. In some instances, the waste can leave a good-sized pit in the finish. Work your way up to 4000-grit sanding materials. At a level of 2000 grit, you should be able to see yourself in the finish.
- Remove the Mold – The next step would be to remove the mold. If it does not want to come out, gently chip away at the foam and Bondo until you can remove it.
- Paint It - The best way to paint it would be to use a paint gun. If you want a piano finish then use only resin, if you want an opaque finish then mix the pain with a coloring agent. Either way the idea is to get a smooth finish.