Technical data

13773-001
51-20
Page 3130 Nov 2000
B. Repair Techniques
One or more of the following techniques will be used to repair the damage. Expose and prepare the
area as previously described under the section titled “Preparation for Repair”.
WARNING:
Always use twice as many repair plies as the original lay-up in order to assure
that the original strength is achieved.
(1) Outer Laminate Repair
(a) If required, repair the inner laminate and core. (See Figure 51-205)
(b) Determine ply count and orientation. (Refer to 51-20)
Note: The first ply is the smallest. The cover ply is always the last and largest ply.
Cut each ply in the required orientation. Keep template and ply together. If
available, cut a section of peel ply large enough to cover the last ply.
(c) Make a repair template for each ply being repaired. Make one additional template, offset
the outer edge of the taper by 0.75 to 1.0 inch. The additional ply is sacrificial, it covers the
entire repair and protects the repair plies during finishing operations. This ply will be called
the cover ply.
(d) If the core was repaired, lightly sand the cured filler paste to remove ridges, feather the
edges and prepare for bonding. If core section was replaced it may be necessary to sand
it down to the level of surrounding core. Small core gaps can be filled at this time with filler
paste; fill after the core area has been prepared for bonding.
CAUTION: Be careful not to cause separation between core and outer laminate when
sanding the outer laminate to a 50:1.
(e) Sand the edge of the outer laminate to a 50:1 taper using 80-grit sandpaper.
(f) Remove all dust and debris with clean oil free compressed air and a vacuum.
(g) Check for any separation of the laminate to the core. Continue to sand back until all sepa-
rated laminate is removed.
Note: Moisten cloth with cleaning solvent. Never pour solvent directly onto lami-
nate, allowing laminate to soak up cleaning solvent.
(h) Solvent clean bonding surfaces of outer laminate with isopropyl alcohol. (Refer to 20-30)
(i) Use MGS L418/418 resin and lay up repair plies. Transfer plies over center of puncture on
outer laminate.
(j) If required, install lightning protection (expanded metal mesh or EMM) with a 0.20-inch
overlap onto the adjacent EMM strips over the last repair ply installed. The original EMM
must be lightly sanded until it becomes shiny. Clean and shiny EMM will assure good elec-
trical continuity. (Refer to 51-00).
(k) Using 80-grit sand paper or finer, lightly sand the area until the EMM is exposed. Exposed
EMM will have a shiny appearance when sanded. During sanding, periodically clean the
area to ensure that the EMM is not being damaged.
CAUTION: Do not continue to sand EMM after it becomes shiny. The EMM is very thin
and can easily be sanded through.