By Karl Kirschenman, ALLDATA Collision Product Manager
Did you hear the one about the vehicle that collided with a
collision shop? No joke… It really happened in Texas in early
2014. An SUV demolished a collision shop’s wall and ended up on
its roof inside a storage area. No word on whether or not that
particular shop was selected for the repair.
Most vehicles probably do not enter your shop in such a dramatic
fashion. But what IS dramatic is the way vehicles are being
constructed these days. Cars and trucks built with new materials
– advanced steels, aluminum, carbon fiber, and plastics have
replaced those heavyweight steel models that used to rule the
You have, no doubt, heard of the enormous ‘plastic islands’ –
huge concentrations of plastic waste – that are found in the
world’s oceans. Ford® is helping relieve the situation a bit by
collecting millions of clear plastic bottles – not to turn in for
nickels, but to recycle as vehicle components. For a few years
now, manufacturers have been incorporating recycled materials
into their cars. The Ford Focus®, for instance, has seats made,
in part, from those recycled bottles (about 22 per vehicle). But
many other components are also plastic.
These are a few plastics that shops like yours have to deal with:
Thermosetting plastics – Cannot be remolded and require a
2-part adhesive for repair.
Sheet-Molded Composites – A type of thermosetting plastic,
which Ford uses in fenders, hoods and liftgates.
Thermoplastics – Can be remolded repeatedly by reheating, and
are used as interior trim components, wheel flares, body side
cladding and bumper covers.
Polyolefins – Thermoplastics with an oily or waxy feel when
sanded or ground. Adhesive materials and paint will not stick to
polyolefins unless an adhesion promoter is first applied.
Polyolefins are used in bumper covers, fan shrouds and wheel
Ford publishes a great deal of information on identifying and
repairing the plastics used in its vehicles. Here is just part of
Ford’s OEM information specifically describing a sheet-molded
composite (SMC) panel repair:
Always wear protective equipment including eye protection
with side shields, and a dust mask when sanding or grinding.
Failure to follow these instructions may result in serious
Always refer to MSDS when handling chemicals and wear
protective equipment as directed. Examples may include but are
not limited to respirators and chemically resistant gloves.
Failure to follow these instructions may result in serious
In deciding whether to repair or install a new component,
follow these guidelines.
Is a new part readily available?
Can the damaged part be economically returned to its
original strength and appearance, or will the labor cost
exceed the cost of a new component?
Will repair provide for the fastest, highest quality
Never apply solvents such as lacquer thinner or reducer
at any stage of plastic repair. Solvents, cleaners and water
are absorbed by many types of plastics and by the glass
fibers used for reinforcements. If this occurs, the plastic
may swell in the area of repair and cause the repair to fail.
Remove cleaners and water quickly and use air and heat to
speed up drying.
During the repair of many plastics and particularly
polyolefin plastics, an adhesion promoter must be applied to
the substrate to allow repair materials and paint to bond
correctly. Reapplication is required when grinding or sanding
through the sealer or primered layers.
NOTE: When possible, it is recommended to
carry out as much of the plastic repair as possible on the
vehicle. Parts mounted on the vehicle are held in correct
alignment throughout the repair. Attempting to repair the
part off the vehicle may cause misalignment. This could
lead to failure of the repair.
Always refer to the manufacturer’s label directions for
the type of repair materials, fillers and bonding agents
being used as they are material specific.
The following procedure applies to repair of structural
cracks and large gouges. If damage is cosmetic, use of
reinforcing cloth may not be necessary.
Panels to be repaired should be dry and at room
temperature 18 C (64.4 F) to 24 C (75.2 F) prior to carrying
out any repairs. Both sides of the panel must be thoroughly
cleaned before sanding or grinding.
Cover the break in the SMC (front and back) with masking
tape. This protects the damaged area from absorbing the prep
cleaner and eliminates wicking of the cleaner through the fibers
into the SMC.
Remove all waxes, silicones, dirt and road oils from the area
surrounding both sides of the damaged area with a plastics wax
and grease remover.
Remove the tape and sand the back of the repair area with
an angle grinder, D/A sander or by hand using 80-grit
sandpaper. Remove all dust with a vacuum and tack cloth.
Create a reinforcing patch using a piece of scrap SMC that
conforms well to the back of the damaged area or form a patch
from fiberglass cloth.
Cut a section of cloth large enough to cover the repair,
plus 25.4 mm (1 in) around the repair area.
Cut a section of plastic film backing approximately 25.4
mm (1 in) larger than the cloth. Lay the plastic on a smooth,
flat surface where it will be used to create a pyramid patch.
Follow manufacturer’s directions and apply plastic repair
adhesive to the plastic film backing and smooth with plastic
spreader to recommended thickness. Place the pre-cut fiberglass
cloth on the adhesive-coated plastic film. Cover the cloth with a
coat of repair adhesive and spread to the recommended thickness.
Apply the prepared patch to the backside of the panel and
compress. Follow manufacturer’s instructions for adhesive cure.
Remove plastic film after adhesive cures and sand as necessary to
Remove masking tape from the front side of damaged area and
grind down to the backing patch. Use an angle grinder with a 30
to 40-grit wheel. Make a gradual taper in the area. This will
prevent bull’s-eyes or read-through in the finished repair. Sand
prepared area with a D/A sander or hand-sand with 80-grit
Build a pyramid patch using fiberglass cloth or equivalent
and plastic repair adhesive. Following manufacturer’s directions,
apply patch to damaged area.
Rough-grind area to remove excess adhesive. Sand repair area
with 80-grit sandpaper, making sure to cut slightly below the SMC
finished surface. This will allow for a finish coat of plastic
body repair material.
Apply a finish coat of plastic repair filler material per
Finish-sand, prime and topcoat using Ford-approved paint
NOTE: This repair/service information is
excerpted from information published by the vehicle manufacturer,
and is intended for the purpose of promoting OE collision repair
information to trained, professional technicians with the
knowledge, tools and equipment to do the job properly and safely.
Before attempting any repairs described, refer to the complete
article in ALLDATA Collision
S3500. It is recommended that these procedures not be
performed by “do-it-yourselfers.”