1 Where damage takes the form of a scratch
which may or may not penetrate the skin of the
car, the two main requirements are to replace
the lost panel strength and fill the damage flush
with the original surface.
Figure 16.41 Removing temporary moulds
Figure 16.39 Applying chopped strand mat
Figure 16.40 Rolling
9 Impregnate each layer with resin, and roll
with a split washer roller to pack down the
fibre glass and resin (Figure 16.40).
10 Allow the repair to cure and then remove the
temporary moulds (Figure 16.41).
11 Clean up the area of repair, removing all surplus
resin and glass and trimming and smoothing
any raw edges.
12 File and sand the repair smooth and, if necessary,
finish with a proprietary polyester filler.
Normal car painting procedure is then carried
out (Figure 16.42).
566 Repair of Vehicle Bodies
2 The damage will generally extend for some distance
around the scratch, and this must be
removed.
3 Again the edge of the cut-out should be scarfed
and, as the repair will be carried out from the
inside of the body, scarfing should be on the
outside.
4 When repairing relatively flat surfaces which
are near vertical, it is easier to impregnate the
chopped strand mat with polyester resin on the
bench. Lay down a piece of cellophane slightly
larger than the patch and paint this with resin.
Place the glass fibre mat into the resin and complete
impregnation by stippling on more resin.
5 Extract air from the laminate while still on the
bench, using the split washer roller. When
removing them from the bench, lift the cellophane
and the laminate together.
6 Use self-adhesive tape to cover the cut-out area
from the outside of the body. A smoother surface
will be obtained if this is backed by a solid
flexible former. Paint resin on to the mould
from inside the body, ensuring that it fills the
scarfed edge completely.
7 Apply the laminate complete with cellophane
to the inside of the repair and press into contact
through the cellophane (the cellophane should
be left in position until the repair is cured).
8 After curing, strip off the cellophane and the
former and adhesive tape from the outside of
the body. The repair is completed by filling
imperfections with polyester resin, after this
has cured, by normal smoothing, flatting and
painting.
Repairs to a blind panel
On occasion it is impossible to reach both sides
of a damaged panel. In such a case repair is more
difficult but can be still carried out. When removing
the damaged section of laminate, cut the
panel back to form a rectangle. Prepare a separate
moulding larger all round than the rectangle
but still sufficiently small to pass through the
panel.
When this patch is cured, fix a loop of wire
through two holes in the centre. Apply resin and
chopped strand mat to the rough surface of the
cured laminate, leaving the centre free. Insert the
prepared patch through the panel, keeping hold of
the wire loop. Using a convenient lever, apply
pressure to pull the patch into contact with the
reverse side of the body panel and allow to cure.
Remove the wire loop and fill the repair flush
with the original body panel using chopped strand
mat and polyester resin. Finish off resin rich, and
cover with cellophane and squeegee to give a
smoother finish. After cure, remove the cellophane
and proceed with normal filling, flatting
and painting.
Replacing part components
The techniques for freeing composite body components
and for replacing part of a component are
shown in Figures 16.43 and 16.44. Special clamps
are available for holding composite body panels in
alignment while they are under repair and being
bonded in place (Figure 16.45).
Important points in reinforced
Composite material repair
1 The strength and ultimate surface finish of a
repair will depend to a great extent on thorough
preparation of the damaged area.
2 If either the damaged area or the repair materials
are at all damp, the strength and life of the
repair will be seriously affected.
Figure 16.42 Finishing the laminate repair
Reinforced composite materials 567
Figure 16.44 Refitting lower quarter panel by bonding (Lotus Engineering)
Figure 16.43 Removing lower quarter panel on
Lotus Elan (Lotus Engineering). Before removing the
lower quarter panel it will be necessary to remove the
boot lid, rear top shell and rear transom.
1 Using a router, cut through the rear of the lower
quarter panel just above the undertray.
2 Carefully rout along a line 40 mm above the
undertray and following the rear wheel arch to the
B-post cover.
3 Using the appropriate Lotus panel tool, separate
the lower quarter panel from the B-post cover and
discard.
4 Using the Lotus panel tool, separate the
remaining section of the lower quarter panel from
the undertray.
5 Using a 36 grit paper and mechanical sander,
remove all old adhesive from the undertray and
B-post cover.
stand at least overnight, or longer if the weather
is particularly cold.
4 The glass fibre reinforcement provides the
strength of the repair, and either chopped
strand mat or cloth must be used to achieve
the required strength. It is not sufficient to
embed layers of glass tissue in polyester
resin.
16.10 Common faults in moulded
laminates
Many complaints concerning the appearance and
performance of these mouldings stem from the
basic cause that the resin is undercured. There
are, however, several problems in the form of visible
flaws or other defects, the remedies of which
will become apparent from the analysis of the
causes.
Wrinkling
This is caused by solvent attack on the gel coat by
the monomer in the laminating resin due to the fact
that the gel coat is undercured. Wrinkling can be
avoided by ensuring that the resin formulation is
correct and the gel coat is not too thin, and by controlling
temperature and humidity and keeping the
work away from moving air, especially warm air. If
the workshop is equipped with hot air blowers,
these should be directed away from the moulds
(Figure 16.46).
3 Many repairs are ruined by attempting to
smooth off or polish before the resin is thoroughly
cured. Any repair should be allowed to
568 Repair of Vehicle Bodies
Figure 16.45 Centring and aligning composite
components using special clamps (Lotus
Engineering)
(a) Side components (front wing, front and rear
door external panels, rear wing) are centred
and aligned with respect to each other, using
tools available in the form of a kit.
(b) Kit comprises: six flat plates, two profiled plates.
(c) Function: vertical adjustment by means of the
shape of the profiled plate fitting in the recess
between the parts.
(d) Clearance 5.5 mm, obtained by the diameter of
locking pin (1) with the components in contact
with one another.
(e) Alignment obtained by the flat of plates (2).
Reinforced composite materials 569
Figure 16.46 Wrinkling (Scott Bader Co. Ltd)
Figure 16.45 (continued)
(f) Fitting and locking: each component is locked
in place on the side of the component which is
not replaced (3) (except when replacing a rear
door panel with a rear wing). Leave the adhesive
to harden for 30 minutes before removing the
tools.
Do not open the door or doors when the tools are
fitted on them: there is a risk of damaging the panel
or the tools.
Pin-holing
Surface pin-holing is caused by small air bubbles
which are trapped in the gel coat before gelation. It
occurs when the resin is too viscous, or has a high
filler content, or when the gel coat resin wets the
release agent imperfectly (Figure 16.47).
Figure 16.47 Pinholing (Scott Bader Co. Ltd)
