The goal is to be cautious and develop good habits. Follow the manufacturer's instructions, check your measurements several times before mixing, work outdoors or in well-ventilated area and be aware of fire dangers that may be posed by fumes and by overheating the resin mixture.
FIBERS OF GLASS
Of course, resin is only half of the equation. The other component is the glass fiber reinforcement. Modern fiberglass design includes a wide range of exotic reinforcements such as Kevlar and carbon fiber, but I'll stick to the common materials that are widely available and reasonably priced.
Paul EsterleAbove is fiberglass mat. Below is fiberglass cloth (inside) and roving (outside).
Glass fibers are exactly that: molten glass spun into fine fibers that are then processed into different types of reinforcement. The first type is fiberglass mat. Strands of fiberglass are cut into short lengths and randomly compacted into a felt-like material. The strands of glass are held in place by means of a glue or sizing applied to the mat.
Chemicals in the resin dissolve the sizing, allowing the mat to conform to whatever it is applied to. The short length of the glass fibers makes it weaker than other types of reinforcement, but it adds thickness and stiffness to a molded part more quickly than other options.
Woven roving is another common type of fiberglass reinforcement. This material is like cloth, but made with extremely thick yarns. It is much stronger than mat, but working with it requires more resin and more effort. Typically, this course material is used in combination with fiberglass mat, which helps fill in the roving's rough surface and eliminates the possibility of air bubbles in the matrix.
Fiberglass cloth is also available in a variety of sizes and weights. It is usually measured in ounces-per-yard, as in "9-ounce-per-yard" cloth. It is available in pre-cut packs, as well as tape and rolls, with widths ranging from 1 to 50 inches. Weights can range from fractions of an ounce to nine ounces or more per yard. The cloth is stronger than mat and conforms to surfaces better than woven roving. A common use of fiberglass cloth is sheathing plywood boat hulls. The fiberglass eliminates problems with the plywood "checking" or cracking, and improves both strength and stiffness. Cloth is often used in moldings where higher tensile strength is needed.
THE APPLICATION
This first application will usually be a layer of mat. After cutting the mat to size, lay it in the mold and brush on a coat of resin. Use cheap, throwaway brushes because cleaning them will be nearly impossible. Work the resin into the mat until the mat turns translucent.
Make sure you work out any air bubbles from each layer. This can best be done with a grooved fiberglass roller. These rollers force air bubbles to the surface, and insure good contact with the layer below. After the initial layer, you can add more mat, roving or cloth to build the project up to its final thickness.
Pay attention to the resin-to-reinforcement ratio. Ideally, this should be 50 percent resin and 50 percent reinforcement. On a practical level, that ratio is nearly impossible to achieve without more advanced techniques, but make every effort to contain your enthusiasm for applying resin. Use just enough to completely wet the reinforcement and insure good contact. Often, you'll end up using more resin than is ideal, but try to minimize overuse as best you can.
Paul EsterleThe author created a jig to keep the project steady and to shape while he glassed.
On my refrigerator lid, I started by applying a small amount of fiberglass filler to the inside corners of the pan (I did not use gel coat). I smoothed these out with the end of a popsicle stick and immediately applied a coat of resin, followed by a layer of two-inch wide fiberglass tape. This stiffened up the pan and sealed up the edges.
The upper edges of the pan were a little floppy and bowed. To keep things straight, I clamped pieces of plywood to each side and placed each side of the pan down on a piece of waxed paper as I glassed the sides. I was more interested in stiffness than looks, so I built up each side and bottom with several layers of mat, rolled with my grooved roller. This resulted in a stiff, strong pan that I then bonded to the teak frame of the lid.
FINISH WORK
Keep in mind that projects involving a temporary mold will not give you a finished surface, and you'll have some work ahead to complete your project and make it pretty.
