Straight edged and pinked tapes are available. The pinking  provides greater surface area for adhesion of the edges and  a smoother transition into the fabric covering. Only tapes  approved in the STC under which work is being accomplished  may be used to be considered airworthy.  Finishing tapes from one to six inches in width are used.  Typically, two inch tapes cover the rib lacing and fuselage  seams. Wing leading edges usually receive the widest tape  with four inches being common.  [Figure 3-33]  Bias cut tapes  are often used to wrap around the curved surfaces of the  airframe, such as the wing tips and empennage surface edges.  They lay flat around the curves and do not require notching.  Finishing tapes are attached with the process adhesive or  the nitrate dope sealer when using a dope-based process.  Generally, all chordwise tapes are applied first followed by  the span-wise tapes at the leading and trailing edges. Follow  the manufacturer’s STC or AC 43.13-1 instructions. The sealer coat in most fabric covering processes is applied  after all finishing tapes have been installed unless it was  applied prior to rib lacing as in a dope-based finishing  process. This coat saturates and completely surrounds the  The FAA-certificated mechanic must strictly adhere to all  instructions for thinning, drying times, sanding, and cleaning.  Small differences in the various processes exist and what  works in one process may not be acceptable and could ruin  Fabric primer is a coating used in some approved covering  processes that combines the sealer and fill coatings into one.  Applied to fabric after the finishing tapes are installed, these  fabric primers surround and seal the fabric fibers, provide  good adhesion for all of the following coatings, and contain  UV blocking agents. One modern primer contains carbon  solids and others use chemicals that work similarly to sun  block for human skin. Typically, two to four coats of fabric  primer are sufficient before the top coatings of the final finish  are applied.  [Figure 3-34] With the sealer coats installed and dried, the next step  provides protection from UV light, the only significant cause  of deterioration of polyester fabric. Designed to prevent UV  light from reaching the fabric and extend the life of the fabric  indefinitely, these coating products, or fill coats, contain  aluminum solids premixed into them that block the UV rays.  They are sprayed on in the number of cross coats as specified  in the manufacturer’s STC or AC 43.13-1 instructions under  which work is done. Two to four cross coats is common.  Note that some processes may require coats of clear butyrate  before the blocking formula is applied.  fibers in the polyester fabric, forming a barrier that keeps  water and contaminants from reaching the fabric during  its life. It is also used to provide adhesion of subsequent  coatings. Usually brushed on in a cross coat application for  thorough penetration, two coats of sealer are commonly used  but processes vary on how many coats and whether spray  coating is permitted. Figure 3-32.  A strut fitting and cable guide with reinforcing fabric  gussets cemented in place.  Figure 3-33.  Cement is brushed through a four-inch tape during  installation over the fabric seam on a wing leading edge. Two-inch  tapes cover the wing ribs and rib lacing. Coating the Fabric 3-22