h. Pour out a small amount of resin, add catalyst and mix thoroughly, using a cutting motion rather than
stirring. Use no fibers.
i. Using the tip of a putty knife or fingertips, fill the hole to about 1 /16 inch above the surrounding surface
with the gel coat mixture.
partially cured.
k. After trimming the patch, immediately place another small amount of gel coat on cut edge of the patch and
cover with cellophane. Then, using a squeegee or other suitable tool, squeegee level with area surrounding the
patch, leave the cellophane on patch for one or two hours or overnight, for complete cure.
l. After repair has cured for 24 hours, sand the patched area using a sanding block with fine wet sandpaper.
Finish by priming, sanding and applying color coat.
4-53. FIBERGLASS FRACTURE AND PATCH REPAIRS.
a. Remove wax, oil and dirt from around damaged area with acetone, methylethylketone or equivalent.
b. Using a key hole saw, electric saber saw, or sharp knife cut away ragged edges. Cut back to sound
material.
c. Remove paint three inches back from around damaged area.
d. Working inside the structure, bevel the edges to approximately a 30° angle and rough-sand the hole and the
area around it, using 80 grit dry paper. Feather back for about two inches all around the hole. This roughens the
surface for a strong bond with patch.
e. Cover a piece of cardboard or metal with cellophane. Tape it to the outside of the structure covering the
hole completely. The cellophane should face toward the inside of the structure. If the repair is on a sharp contour
or shaped area, a sheet of aluminum formed to a similar contour may be placed over the area. The aluminum
should also be covered with cellophane.
f. Prepare a patch of fiberglass mat and cloth to cover an area two inches larger than the hole.
g. Mix a small amount of resin and catalyst, enough to be used for one step at a time, according to kit
instructions.
h. Thoroughly wet mat and cloth with catalyzed resin. Daub resin on mat first, and then on cloth. Mat
should be applied against structure surface with cloth on top. Both pieces may be wet out on cellophane and
applied as a sandwich. Enough fiberglass cloth and mat reinforcements should be used to at least replace the
amount of reinforcements removed in order to maintain the original strength. If damage occurred as a stress
crack, an extra layer or two of cloth may be used to strengthen the area.
i. Lay patch over hole on inside of structure, cover with cellophane, and squeegee from center to edge and to
remove all air bubbles and assure adhesion around edge of hole. Air bubbles will show white in the patch and
they should be worked out to the edge. Remove excess resin before it gels on the part. Allow patch to cure
completely.
j. Remove cardboard or aluminum sheet from outside of hole and roughen the patch and edge of hole.
Feather edge of hole about two inches into undamaged area.
k. Mask area around hole with tape and paper to protect surface. Cut a piece of fiberglass mat about one inch
larger than the hole and one or more pieces of fiber cloth two inches larger than the hole. Brush catalyzed resin
over hole, lay mat over hole and wet out with catalyzed resin. (Use a daubing action with a brush). Then apply
additional layer or layers of fiberglass cloth to build up patch to the surface of structure. Wet out each layer
thoroughly with resin.
l. With a squeegee or other suitable tool, work out all air bubbles in the patch. Work from center to edge,
pressing patch firmly against the structure. Allow patch to cure for 15 to 20 minutes.
m. As soon as the patch begins to set up, but while still rubbery, take a sharp knife and cut away extra cloth
and mat. Cut on outside edge of feathering. Strip cut edges of structure. Do this before cure is complete, to save
extra sanding and allow patch to cure overnight.
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
STRUCTURES
1F6
Issued: FEBRUARY. 28, 1989
