When accomplishing a repair on a vertical surface,
to the second chalk mark (fig. 4-12). This increases
use a plate on each side of the patch to hold the patch
the area to which the patch will adhere so that a
stronger bond may be obtained. The roughened
in place while it is curing. Cover these plates with
surface caused by the coarse abrasive provides a better
separating film so that they may be removed easily
bond between the old surface and the patch. After the
later. Hold the plates in place by taping, shoring, or
grinding has been completed, wipe away all the
bracing them with lumber (fig. 4-13).
sanding dust and clean the entire adjacent area with
If the underside of the damaged area is
acetone or lacquer thinner.
inaccessible, apply a resin-wetted backup patch about
The procedure just described is for preparing a
2 inches larger than the hole into the scarfed area on
damaged area for the application of a patch on one
the exposed side. This patch should be allowed to cure
side. The patch will generally be placed on the readily
(harden) to form a foundation for the patching
accessible external surface, because it provides greater
material. After the backup patch has hardened, lightly
resistance to external stresses. However, in instances
sand the surface to provide a better bond between it
where maximum strength is necessary in both
and the material to be added later.
directions, and both sides are readily accessible, it may
TAILORING THE REINFORCEMENT
be desirable to make a patch on both sides (view C of
MATERIAL.--To cut the glass reinforcement to fit
fig. 4-7). Both sides are prepared in the same manner
the repair, prepare paper templates for the innermost
as a repair to one side. Then, the patch must be made
ply that are slightly larger than the hole, and for the
on both sides. Repairs of this type are especially
outermost ply to barely overlap the scarfed area. Each
desirable for thick laminates (three-eighths of an inch
of the intermediate plies should be cut proportionally
and over). Apply the temporary backing plate to
larger than the preceding smaller ply. (See fig. 4-9 for
support the patch while it is curing (hardening). For
the approximate number of plies required for a given
small repairs on flat surfaces, the backing plate can be
thickness.) If the patch is being made from both sides,
a piece of heavy cardboard, plywood, or sheet metal.
two sets of plies should be tailored as described, one
For curved areas, a formed piece of aluminum or steel
for each side.
sheet metal is generally preferred.
Figure 4-12.--Scarfing operation.