Repairing a body scratch or gash

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 16.41Removing temporary moulds

Figure 16.39Applying chopped strand mat

Figure 16.40Rolling

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).

566Repair 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 16.42Finishing the laminate repair

Reinforced composite materials 567

Figure 16.44Refitting lower quarter panel by bonding (Lotus Engineering)

Figure 16.43Removing 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

568Repair of Vehicle Bodies

Figure 16.45Centring 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 16.46Wrinkling (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 16.47Pinholing (Scott Bader Co. Ltd )