similar techniques for the most common types of face sheet  materials, such as fiberglass, carbon, and Kevlar$^{®}$. Kevlar ®  is often repaired with fiberglass.  [Figure 7-54] A temporary repair meets the strength requirements, but is  limited by time or flight cycles. At the end of the repair’s life,  the repair must be removed and replaced. An interim repair  restores the required strength to the component. However,  this repair does not restore the required durability to the  component. Therefore, it has a different inspection interval  and/or method. A permanent repair is a repair that restores  the required strength and durability to the component. The  repair has the same inspection method and interval as the  original component.  A potted repair can be used to repair damage to a sandwich  honeycomb structure that is smaller than 0.5 inches. The  honeycomb material could be left in place or could be  removed and is filled up with a potting compound to restore  some strength. Potted repairs do not restore the full strength  of the part. Potting compounds are most often epoxy resins filled with  hollow glass, phenolic or plastic microballoons, cotton, flox,  or other materials. The potting compound can also be used as  filler for cosmetic repairs to edges and skin panels. Potting  compounds are also used in sandwich honeycomb panels  as hard points for bolts and screws. The potting compound  is heavier than the original core and this could affect flight  control balance. The weight of the repair must be calculated  and compared with flight control weight and balance limits  set out in the SRM. Note: the following steps are not a substitution for the aircraft  specific Structural Repair Manual (SRM). Do not assume that  the repair methods used by one manufacturer are applicable  to another manufacturer. Thin laminates can be visually inspected and tap tested to  map out the damage.  [Figure 7-55]  Thicker laminates need  more in-depth NDI methods, such as ultrasonic inspection.  Check in the vicinity of the damage for entry of water, oil,  fuel, dirt, or other foreign matter. Water can be detected with  X-ray, back light, or a moisture detector.  Water needs to be removed from the core before the part is  repaired.  [Figure 7-56]  If the water is not removed, it boils  Step 2: Remove Water From Damaged Area Step 1: Inspect the Damage Damage Requiring Core Replacement and Repair  to One or Both Faceplates Sandwich Structures Damage Classification Minor Core Damage (Filler and Potting Repairs) L I $_{B}$E R T Y 2 0 8 Tap test with tap hammer Instrumented tap test Coin tap test External Internal Scarf Patch Adhesive Composite skin Core Core splice adhesive Repair core Repair plug Figure 7-54.  Typical repairs for honeycomb sandwich structure. Figure 7-55.  Tap testing techniques. 7-34