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.
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