First we cut a piece of speaker grille cloth (or fiberglass-shaping material) that is large enough to cover the top of our enclosure. Drape it over the top.
In our last installment (August 2005) we created the frame for the top of our multi-composite enclosure. Now it's time to cover it with some fiberglass mat and resin. Unlike the bottom shell, where we had a solid surface to lay our fiberglass mat on, we only have a frame of "ribs" at this point. Although it is theoretically possible to apply fiberglass mat or cloth directly over this frame, the difficulty of doing so and the messy end result would leave much to be desired. To create a relatively smooth shape on our frame, we will stretch a "fiberglass-shaping material" over it, to which we can subsequently apply layers of fiberglass mat for strength.
What exactly is "fiberglass-shaping material"? Although this is subject to much debate, it can be a variety of different materials, as long as it's stretchable and absorbs fiberglass resin. There is no exact science to picking a material, and it doesn't need to be a particular blend of fibers. I've read false claims on Internet forums that the fiberglass-shaping material must be a 50/50 blend of polyester and cotton. As long as there aren't any chemicals in the material that prevent the resin from curing (I haven't seen one yet), the exact blend of fibers shouldn't make any difference. Popular materials are speaker grille cloth, t-shirt fabric, fleece, stretchable speaker box carpet and "custom mold fabrics." I don't recommend using thicker materials like the speaker box carpet because they soak up too much fiberglass resin and tend to warp. Fiberglass resin and "shaping material" without fiberglass mat (or other strengthening material) is brittle and prone to cracking. Using a fuzzy material should also be avoided because it can create a coarse texture when the resin cures, making it necessary to sand the entire surface smooth before reinforcing it with fiberglass mat. I highly recommend using a light colored speaker grille cloth (which just happens to be readily available in most car audio shops) or a thin, smooth material similar to it.
Start stapling the cloth to the frame, starting in the middle with the speaker ring. Make sure that the cloth is centered before starting.
Cut a piece of the shaping material that is large enough to drape over the top of the frame with several inches of overhang on each side. The shaping material is fastened to the frame using a pneumatic upholstery staple gun with 3/8" crown 22-gauge wire staples that are 3/16" tall. I highly recommend the Duo-Fast TI-3118A (now called the SureShot 3118) for the professional fabricators out there. You can also use an electric stapler, but they are much more bulky and difficult to use on some projects. It's important not to use staples that are thick or long, as they will crack the frame. With most projects, I work outward from the middle of the frame, starting with the speaker ring. Make sure that the shaping material is centered over the frame and there is enough material to cover the edges before you start. Staple around the ring in the groove that we previously created with our rabbeting router bit. The staples should be placed consecutively with very little space between them.
Once the ring is completely fastened, pull the shaping material at the outer edges of the frame and begin stapling around the perimeter. The shaping material should be taut, but does not need to be as tight as a drum. Stretching too tightly can cause the material to tear. Pull and staple the perimeter in sections from opposing sides so that the material is stretched evenly. Concave sections of the frame that don't make contact with the shaping material need to be fastened with additional staples, but convex sections that already make contact don't. Once everything is securely fastened, carefully cut off the excess shaping material with a sharp razor blade. Take care not to drag the blade across the staples as it will dull it immediately.
After everything is stapled down, carefully trim the excess with a razor blade. | 
Apply a light coat of resin to the cloth. Once it gels, add a second heavier coat of resin to fully saturate the surface. | 
Once the resin has dried, we can begin building up the layers of fiberglass mat. Laying the mat neatly will save grinding time later. |