Apply Fibreglass and Tapes
Fibreglass cloth is applied to surfaces to provide reinforcement and/or abrasion resistance, or in the case of some timbers, to prevent grain checking. It is usually applied after fairing and shaping are completed, and before the final coating operation. It is also applied in multiple layers and in combination with other materials to build composite parts.
Fibreglass cloth may be applied to surfaces by either of two methods. The "dry" method refers to applying the cloth over a dry surface. The "wet" method refers to applying the cloth to an epoxy-coated surface often after the wet-out coat becomes tacky, which helps it cling to vertical or overhead surfaces. Since this method makes it more difficult to position the cloth, the dry method is the preferred method especially with thinner cloth.
1. Prepare the surface as you would for bonding (Surface Preparation).
2. Position the cloth over the surface and cut it several inches larger on all sides. If the surface area you are covering is larger than the cloth size, allow multiple pieces to overlap by approximately two inches. On sloped or vertical surfaces, hold the cloth in place with masking or duct tape, or with staples.
3. Mix a small quantity of epoxy (three or four pumps each of resin and hardener).
4. Pour a small pool of resin/hardener near the center of the cloth.
5. Spread the epoxy over the cloth surface with a plastic spreader, working the epoxy gently from the pool into the dry areas. Use a foam roller or brush to wet out fabric on vertical surfaces. Properly wet out fabric is transparent. White areas indicate dry fabric. If you are applying the cloth over a porous surface, be sure to leave enough epoxy to be absorbed by both the cloth and the surface below it. Try to limit the amount of squeegeeing you do. The more you "work" the wet surface, the more minute air bubbles are placed in suspension in the epoxy. This is especially important if you plan to use a clear finish. You may use a roller or brush to apply epoxy to horizontal as well as vertical surfaces.
Smooth wrinkles and position the cloth as you work your way to the edges. Check for dry areas (especially over porous surfaces) and re-wet them with epoxy as necessary before proceeding to the next step. If you have to cut a pleat or notch in the cloth to lay it flat on a compound curve or corner, make the cut with a pair of sharp scissors and overlap the edges for now.
6. Squeegee away excess epoxy before the first batch begins to gel. Slowly drag the spreader over the fabric at a low (almost flat) angle, using even-pressured, overlapping strokes. Use enough pressure to remove excess epoxy that would allow the cloth to float off the surface, but not enough pressure to create dry spots. Excess epoxy appears as a shiny area, while a properly wet-out surface appears evenly transparent, with a smooth, cloth texture. Later coats of epoxy will fill the weave of the cloth.
7. Trim the excess and overlapped cloth after the epoxy has reached its initial cure. The cloth will cut easily with a sharp utility knife. Trim overlapped cloth, if desired, as follows:
a) Place a metal straightedge on top of and midway between the two overlapped edges.
b) Cut through both layers of cloth with a sharp utility knife, being very careful not to cut too deeply.
c) Remove the topmost trimming and then lift the opposite cut edge to remove the overlapped trimming.
d) Re-wet the underside of the raised edge with epoxy and smooth into place.
The result should be a near perfect butt joint, eliminating double cloth thickness. A lapped joint is stronger than a butt joint, so if appearance is not important, you may want to leave the overlap and fair in the unevenness after coating.
8. Coat the surface to fill the weave before the wet-out becomes tack free. Follow the procedures for final coating in the next section. It will take two or three coats to completely fill the weave of the cloth and provide a thick enough coating to allow for a final sanding that will not affect the cloth.
A variation of this method is to apply the fabric after a wet out coat has cured thoroughly and the surface has been prepared for bonding. This method assures a thorough wet out of the substrate and fabric, and the fabric can still be positioned easily while it is being wet out.
An alternative is to apply the fabric or tape to a surface coated with wet epoxy. As mentioned, this is not the preferred method, especially with large pieces of cloth, because of the difficulty removing wrinkles or adjusting the position of the cloth as it is being wet out. However, you may come across situations, such as applying fabric on vertical or overhead surfaces, when this method may be useful or necessary.
1. Prepare the surface for bonding (Surface Preparation). Pre-fit and trim the cloth to size. Roll the cloth neatly so that it may be conveniently rolled back into position later.
2. Roll a heavy coat of epoxy on the surface.
3. Unroll the glass cloth over the wet epoxy and position it. Surface tension will hold most cloth in position. If you are applying the cloth vertically or overhead, you may want to thicken the epoxy slightly with filler, then wait until it becomes sticky. Work out wrinkles by lifting the edge of the cloth and smoothing from the center with your gloved hand or a plastic spreader.
4. Apply a second coat of epoxy with a foam roller. Apply enough epoxy to thoroughly wet out the cloth.
5. Remove the excess epoxy with a plastic spreader, using long overlapping strokes. The cloth should appear consistently transparent with a smooth cloth texture.
6. Follow steps 7, 8 and 9 under the dry method to finish the procedure.
Any remaining irregularities or transitions between cloth and substrate can be faired by using an epoxy / filler fairing compound if the surface is to be painted. Any additional fairing done after the final coating should receive several additional coats over the faired area.