The Basics Of Fiberglass Fabrication - How To

Starting in the middle with the cloth centered, staple the material down with a pneumatic upholstery staple gun and 31/48" crown 22-gauge wire staples that are 31/416" tall. You can also use an electric stapler, but these are more bulky and difficult to use in some projects. Don't use staples that are too long or thick as they'll crack the frame. Staple around the ring in the rabbeted groove that we previously rabbeted. The staples should be close together.

With the ring fastened, pull the material at the outer edges and staple down the perimeter. It should be taut but not as tight as a drum, which can cause it to tear. Pull and staple opposing sides in sections so the material is stretched evenly. Concave sections that don't make contact with the material need to be fastened with additional staples, but convex sections don't. Cut off extra material with a sharp razor blade.

Mask off the speaker ring, sides of the enclosure and any other area that should be resin free. Apply a light coat of resin over the shaping material. After the first coat dries, apply a second thicker coat, which allows the material to be fully saturated and creates a stiff surface. Once dry, smooth out rough spots and bumps with 50- or 80-grit sandpaper.

Brush a coat of resin over the material and layer on shredded fiberglass. Wet it out with a 2" bristle brush and continue, putting down a full layer at a time in order to keep track of them and apply them evenly. If the resin kicks in and the shell begins to heat up, stop applying the mat and wait for it to cool before starting again.

When finished, let the shell harden and cool, which will take two to three hours.

Even though the shell isn't fully cured, apply fiberglass-reinforced filler to the resin and filler can both cure overnight. Knock down rough spots with 36- or 50-grit sandpaper and mix filler with cream hardener. Different brands require different amounts, so with a new brand, use a stopwatch to see how long it takes to set with the amount of hardener you added.

Use a plastic spreader to fill in any low spots or rough areas with the body filler.

Now you can save some sanding time by waiting for the green stage. After the filler sets and completes its exothermic reaction, it reaches a stage where it can be sanded easily using 36-grit sandpaper. If it rolls off with the paper, wait until it grates like Parmesan cheese.

After waiting overnight for the piece to cure, use an angle die grinder with a 3" and 2" 24-grit Roloc disk to grind down rough edges, high spots and spreader marks until it's close to your desired shape. For areas with more than 0.25" to fill, use more fiberglass-reinforced filler.

For low spots less than 11/48" deep use Rage Gold body filler, which will also smooth out the rest of the surface. Premium body fillers like Rage Gold help create better results with fewer pinholes and are definitely worth the cost.

Lightweight body fillers generally require less hardener (approximately less than half) than fiberglass-reinforced fillers. Do a test batch if you aren't familiar with working with body fillers. A thoroughly mixed batch of filler has a completely uniform color.

Try to get all of the filler on the piece first and then smooth it out rather than smoothing as you go and having unused filler harden on your mixing board. This takes practice.