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9/8/98 AC 43.13-1B deterioration with fabric at least equal to that used by the original manufacturer. If the qual ity is not known, intermediate-grade fabric, meeting TSO-C14b specification, is accept able. Fabric may be installed in sections with a 1/2 inch edge overlap without covering the overlap with finishing tape. Fabric may also be installed with the edges butted together, and the seam covered with a minimum 1-inch wide finishing tape. The seams may be oriented in any direction, in reference to the line of flight. However, overlapped seams, not covered with a finishing tape, should be oriented rearward. Fabric should be wrapped completely around a wing’s leading and trailing edges and other components, where possible, to provide fabric to-fabric continuity around all edges to avoid a poorly-bonded fabric edge from peeling from the plywood surface causing serious aerody namic consequences. a. After the plywood surface is pre- pared, and the two pre-coats of clear dope have dried as recommended in para graph 2-6 g, the fabric is pulled snug and bonded with clear dope around the perimeter of the fabric section. The fabric is then wetted with distilled water to remove fold creases, in the same manner described for fabric panel ar eas. After the water has evaporated, a heavy coat of low-viscosity clear dope is brushed firmly through the fabric to soften the under lying dope pre-coat, insuring a good bond. Brushing techniques should be accomplished by moving the brush from one side across to the opposite side to remove all air bubbles and thoroughly saturate the fabric. This is indi cated by the plywood grain being easily visible through the translucent fabric. Except for very small imperfections or small dents in the ply wood surface, voids are not permissible be tween the fabric and plywood surfaces. Voids may allow the fabric to balloon from the ply wood surface, creating adverse handling char acteristics. b. After the first dope coat has dried at least 1 hour at 70 °F, a second heavy coat of clear dope is applied by brush to fill the fabric weave and prevent pinholes. The installation of finish tape around the perimeter of the ply wood surfaces, leading edges, and other wear points, is optional but recommended for wear and chafe protection. The application of alu minum-pigmented dope coating, sanding, and finish coats will be the same as that specified for fabric panel areas. Reinforcement grom mets are not required on drain holes through plywood surfaces. 2-23. COAT- ING APPLICATION DEFECTS. a. Blushing. The appearance of light shaded dull areas on the surface as dope dries is the result of moisture in the atmosphere condensing on a surface due to the cooling ef fect of the fast-evaporating components of dope thinner escaping from the coating. Blushing can occur at any temperature when the humidity is above 65 percent. There are several ways to remedy this problem. The drying time may be slowed by adding up to 1 quart of blush retarder to 1 gallon of dope or by increasing the temperature of the dope room and eliminating any cooling draft from blow ing across the surface. Blushed surfaces may be reworked by spraying several, closely-timed coats of a 50/50 blend of blush retarder and dope thinner to soften and return the dope sur face to the original liquid state. Blush retarder, mixed with dope, may delay the full drying time by several days, but will eventually es cape from the dope film if the room tempera ture is maintained an average of 70 °F. b. Pinholes. Voids between the fabric threads that are not filled with the first coats of dope are called pinholes. They may be caused by fabric contamination, such as oil or finger Par 2-22 Page 2-29PDF Image | AFS-640
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