Motor vehicle glazing systems
Since the introduction of legislation on the compulsory
wearing of seatbelts for front seat passengers
in the early 1980s, both the type and style of
glass fitted into windscreens have changed. Prior
to 1980, toughened glass, which shatters into tiny,
relatively harmless pieces when broken, and which
can dangerously obscure a driver’s vision, was used
by many vehicle manufacturers. This glass was
indirectly glazed on to the body and secured using
a self-tensioning rubber weather strip fitted to the
aperture. With the seatbelt legislation in force,
however, safety standards were improved, bringing
an increased use of laminated glass, which is the
type that remains in place when broken and therefore
allows the driver to continue the journey.
This resulted in a change in glazing methods,
with laminated glass being increasingly secured
by the process of direct glazing. This is a method
of fitting a glass unit to a vehicle by chemically
bonding it to the prepared aperture using specialized
compound sealants. This method provides two
definite design benefits. It gives an aerodynamic
profile, and also increases the strength of the windscreen,
thus making it safer and more weather
resistant. As well as being easier to fit on the production
line, the majority of direct glazing is now
done by robots. A direct glazed windscreen can
also be replaced to its original specification without
affecting the structural integrity of the vehicle.
Indirect glazed windscreen removal and
replacement
The two basic types of safety glass used in the
car windscreen are laminated and toughened.
Laminated glass is of a sandwich construction and
consists of two pieces of thin glass one on either
side of, and firmly united to, a piece of transparent
reinforcing known as the interlayer (Figure 14.103).
Although such a glass may crack, forming a spider’s
web pattern (Figure 14.104), it holds together and
the panel remains in one piece except under conditions
of the most violent impact. Toughened glass is
produced by the process of heating a solid piece of
glass and then rapidly cooling it so that its liability
to fracture is greatly reduced and its strength
increased to about six times that of untreated glass.
If fracture should take place, the resulting fragments
consist of very small comparatively harmless
particles (Figure 14.104).
In major accident damage, removal and replacement
of the windscreen is an essential feature of
the repair. Many windscreens and rear windows
are held in place by a rubber weatherstrip which
is usually of single-piece construction. Both glass
and any outside trim mouldings, if used, are
recessed into the weatherstrip. It also has a recess
which fits over the body flanges all round the
opening for the glass. It is this portion of the
weatherstrip that holds the entire assembly in
place.
Indirect types of glazing systems can be identified
for each specific model by referring to the
body section of the relevant manufacturer’s repair
manual. The rubber weather seals used are either
mastic sealed, dry glazed, self-sealing or push fit
(Figure 14.105). The self-sealing types are held in
Figure 14.103Laminated glass
Figure 14.104Characteristic breaking pattern of
laminated and toughened glass
466Repair of Vehicle Bodies
place by a removable centre filler strip and can be
either mastic sealed or dry glazed (Figure 14.105c).
All the systems are used with either a rubber
weather strip moulding with a sealing compound
(Figure 14.105a) or a rubber weather strip moulding
without a sealing compound (Figure 14.105b).
The rubber weather strip has two rebates, one
for the glass and one to seat over the metal
flange of the body aperture. It is the contact area
of the aperture that requires careful attention
whenever the glazing is disturbed or removed.
In all cases it is essential that the aperture is
Figure 14.105Indirect glazing system: (a) mastic-sealed (b) dry glazed (c) self-sealing (d) push fit
Major accident damage 467
correctly painted prior to refitting any of the
weather seals.
In order to remove a windscreen which is fitted
with self-tensioning weatherstrip, the following
procedure must be carried out. First cover the
bonnet to protect the paintwork. Then, working
from the inside of the car, remove any instrument
panel mouldings or trim which may interfere with
the removal of the windscreen. Also, working from
the outside of the vehicle, remove any windscreen
chrome mouldings which may be fitted into the
weatherstrip. Again working from the inside and
starting from one of the top corners, pry the rubber
weatherstrip off the body flange with a screwdriver.
At the same time press firmly against the
glass with your hand adjacent to the portion of the
rubber lip being removed, or bump the glass with
the palm of the hand; this should force the entire
assembly over the body flange. The windscreen
can then be removed from the body opening.
To replace the windscreen, first clean the glass
channel in the rubber weatherstrip to be sure
that all traces of sealer and any broken glass are
removed. Place a bead of new sealing compound
all round the weatherstrip in the glass channel.
Work the glass into the glass channel of the weatherstrip
and be sure it is properly seated all the way
round. Lay the windscreen on a bench, suitably
covered to prevent scratching, so that the curved
ends are pointing upwards and in this position the
pull cords used to seat the rubber lip over the body
flange can be inserted into the metal channel on
the weatherstrip (Figure 14.106). One or two cords
may be used. Where two cords are normally used
they can be pulled in opposite directions, which
will make the fitting of the windscreen easier.
Commence with one cord from the bottom righthand
side of the windscreen, leaving about one
foot-spare for pulling. Start the second cord from
the bottom left-hand corner and proceed to the
right, following round up to the top left-hand
corner. Apply sealer all round the metal lip on
the body aperture. Place the entire unit in the
windscreen opening with the cord ends hanging
inside the vehicle. An assistant can help by pressing
against the glass from the outside while each
cord is pulled out of the groove. As the cord is
pulled out, the rubber lip is seated firmly over the
body flange. A rubber mallet can be used to tap
the unit around the outside so as to seat the entire
windscreen assembly firmly in place. Any surplus
sealer can be cleaned off with white spirit.
The procedure for removing a windscreen fitted
with self-sealing weatherstrip is first to locate the
joint in the filler strip which runs right through
the centre of the weatherstrip. The strip is then
carefully eased up and pulled out slowly around
the entire assembly. This relieves the tension on the
glass which can then be lifted out of the weatherstrip
by easing one corner first. To replace this type
of windscreen the metal lip on the body aperture is
sealed with a sealer, the appropriate channel in the
weatherstrip is then placed over this lip and seated
all the way round the body aperture. The windscreen
is fitted into the glass channel on the weatherstrip
with the aid of a special tool which enables
the glass channel lip to be lifted, thus allowing
the glass to slip easily into position. A small brush
is used to apply a solution of soap and water to
the filler channel. This assists the filler strip installation.
A specially designed tool is used to insert
the filler strip into its channel.
Direct glazed windscreen removal
and replacement
The method of direct glazing of windscreens, also
known as bonding, is very popular with motor
manufacturers. This process involves the bonding
Figure 14.106Using pull cords to fit windscreens
468Repair of Vehicle Bodies
of glass into the aperture. Some of the advantages
claimed for direct glazing are as follows:
1 Increased rigidity and strength caused by integration
of the glass into the body of the vehicle,
reducing the need for supporting members and
improving visibility with enlarged glass areas.
2 Weight reduction.
3 Improved aerodynamics by the deletion of rubber
surrounds, aiding fuel economy.
4 A better seal against the weather, eliminating
the need for resealing.
5 Increased protection against car and contents
thefts.
Various bonding materials are used in direct glazing.
Some require heating to induce a chemical reaction
to create adhesion, whilst others will cure at room
temperature.
Polyurethane and silicone materials are usually
supplied as a pumpable tape. They are cold cured
and the material is dispensed on to the glass
through a specially formed nozzle out on the end
of a cartridge. This can be done with the aid of
a hand operated or compressed air cartridge gun.
These materials are highly viscous in their uncured
state, enabling a high degree of manoeuvrability
within the glass aperture to ensure a good seal.
The sealant itself is either one- or two-component
polyurethane. The latter contains an accelerator
compatible with the adhesive; this is applied evenly
to the perimeter of the windscreen (Figure 14.107).
Once this is achieved, the glass is placed into the
aperture using glass suckers and aligned before
securing. When a one-component polyurethane is
used the car can be driven away in four to six
hours: if a two-component polyurethane is used it
takes only 30 minutes to cure, allowing the vehicle
to be back on the road within an hour of the repair
starting.
To remove the glass from the vehicle, the bonding
material has to be cut. This can be achieved by
using a piano wire, a special cutter or a hot knife,
as follows:
Piano wire Before using this method of removal
there are certain safety precautions that should be
observed. Gloves should be worn to protect the
hands, and safety glasses or goggles should be
used for eye protection in the event of the wire or
glass breaking. When the finishers or mouldings
have been removed to expose the bonded area
of the glass, the wire has to be fed through the
bonding. This is done by piercing a hole through
the bonding and feeding the wire through with the
aid of pliers. Handles can be fixed to the ends of
the wire to allow a pulling action (Figure 14.108).
Pneumatic or electric cutter (oscillating) This is
an air or electric powered tool to which special
shaped blades to suit specific vehicle models
are fitted. The tool removes windscreens that
have been bonded with polyurethane adhesives
(see Figure 14.109).
Hot knife The hot knife can be used by one
person cutting from the outside of the vehicle.
It can cut round the average bonded windscreen
and clean off the excess remaining adhesive while
minimizing the risk of damaging the car bodywork.
Before use, all trim around the windscreen,
both inside and outside, should be removed (see
Figure 14.110). The cutting medium is provided by
a heated blade which is placed under the edge of
the glass and pulled around the perimeter, melting
the bonding to release the windscreen. It is used in
conjunction with an air supply, which constantly
blows on to the cutting area of the blade. This
prevents the heat dissipating along the blade and
gives a constant temperature as well as eliminating
smoke and fumes emitted from the cutting operation.
Overheating can result in toxic fumes being
given off and a charcoal filter mask should be worn
as a safety precaution. Before glazing can be
Figure 14.107Direct glazing with moisture-cured
urethane
Major accident damage 469
replaced, the bonding surfaces must be prepared
correctly. The residue of the original sealer left in
the aperture has to be trimmed to ensure there is
a smooth layer for the new sealer to adhere to, and
to allow the glass to seat in the correct position.
Various sealants for windscreen replacement are
available.
The surfaces are then prepared with the materials
included in the individual manufacturer’s glass
replacement kit, that is sealer application gun with
bonding material, suction cups and leak test equipment,
following the instructions provided. There is
little variation in the sequence of operations, which
is typically as follows:
1 Using a sharp knife, trim and level off sealer
remaining in the vehicle windscreen aperture.
Remove loose sealer. Areas where bare metal is
exposed must be treated with etch primer.
Figure 14.108Removing direct glazing using a
piano wire
Figure 14.109Electric windscreen cutter
(Fein/George Marshall (Power Tools) Ltd )
Figure 14.110Welwyn hot knife (Welwyn
Tool Co. Ltd )
470Repair of Vehicle Bodies
2 If the original windscreen is to be refitted, level
off the remnants of the old sealer. Take care not
to damage the black ceramic edging.
3 Apply the cleaning solvent provided in the
repair kit to the windscreen aperture and the
inboard edges of the screen, then wipe both
aperture and screen with a clean cloth.
Warning:when working with solvents and
primers, use PVC gloves or apply barrier cream
to hands.
4 Take the spacer blocks from the repair kit,
remove the adhesive backing, and fit them in the
original position on the windscreen aperture.
Ensure that the differently shaped blocks are
located correctly.
5 Fit the suction cups to the outer face of
the windscreen and place the screen in the
vehicle. Centralize the screen in the body
aperture. Take strips of masking tape and
attach them across the join between the
body and the screen. These strips afford a
guide when finally fitting the screen after
sealant has been applied. Cut the masking
tape strips at the glass edges and remove the
screen.
6 Shake the tin containing the glass primer for
at least 30 seconds. Then, using the felt swab,
apply the primer evenly along the screen
perimeter. When dry, wipe with a clean cloth.
Repeat the above process, this time by cutting
the applicator head and using it to apply a coat
of primer 17 mm wide (0.7 in) to the windscreen
aperture.
7 Immerse a cartridge of sealer in water at a temperature
of 60 °C for approximately 30 minutes.
Pierce the sealer cartridge in the centre of its
threaded end and fit the precut nozzle. Remove
the lid from the other end, shake out any
crystals present and install the cartridge in the
applicator gun.
8 Apply the sealer in a smooth continuous bead
around the edge of the windscreen. The sealer
bead should be 12 mm (0.5 in) high and 7 mm
(0.25 in) wide at its base.
9 Lift the screen using the suction cups and offer it
up to the vehicle, top edge leading. Carefully
align the masking tape strips, then lower the
screen into position. Remove the suction cups.
Testing for leaks, using either leak testing equipment
or spraying with water, may be carried out
immediately.
Caution: if a leak or leaks are detected, apply
sealer to the area and retest. Do not remove
the screen and attempt to spread the sealer
already applied.
10 If leaks are not present, fit the windscreen finishers.
Heat the windscreen finishers to 45 °C
and, commencing at one end of the screen
lower corners, press into position around its
entire perimeter. Remove the fascia’s protective
covering. Trim the lower spacer blocks.
Fit retaining clips as necessary.
11 Fit the windscreen wiper finisher panel and
air intake mouldings and the wiper arms and
blades.
Caution: do not slam the vehicle’s doors with
the windows fully closed until the screen is
fully cured.
Warning:the integrity of the vehicle’s safety
features can be impaired if incorrect windscreen
replacement bonding materials and fitting instructions
are used. The manufacturer’s instructions
should be adhered to at all times.
Water leak detection
The general principles for searching for the actual
location of where water leaks could potentially
occur on the vehicle are not specific to any particular
model and can apply to all vehicles.
First start by obtaining as much information as
possible from the customer as to when, where and
how the leak occurs, and also whether the water
appears to be clean or dirty. If these facts are not
known, considerable time could be spent checking
the wrong areas of the vehicle.
Tools and equipment
The following tools and equipment are
recommended:
Garden spray (hand pump pressure type)
Wet/dry vacuum cleaner
Torch
Mirror
Seal lipping tool
Trim panel removing tool
Small wooden or plastic wedges
Dry compressed air supply
Hot air blower
Sealant applicator
Ultrasonic leak detector.
Major accident damage 471
Locating the leak
Locating the source of the water leak involves a
logical approach together with a combination of
skill and experience. For the purpose of locating
the leak the vehicle should be considered in three
specific areas: the front interior space, the rear
passenger space, and the boot space. From the
information provided by the customer the body
repairer should be able to determine which area
is the right one on which to concentrate.
Having identified the area of the leak, the
repairer must find the actual point where the
water is entering the vehicle. An ordinary garden
spray, of the type which can be pressurized and
adjusted to deliver water in the form of a very fine
spray or a small powerful jet, has been found to
be very effective in helping to locate most leaks.
Using a mirror and torch will help to see into any
dark corners.
Testing
The sequence of testing is particularly important.
Always start at the lowest point and work upwards.
The reason for this is to avoid masking a leak
in one place while testing in another. If for example
testing was to commence around the windscreen,
water cascading down could leak into the car via
the heater plenum or a bulkhead grommet.
However, it could be wrongly assumed that the
windscreen seal was at fault.
The visible examination of door aperture seals,
grommets and weather strips for damage, deterioration
or misalignment, as well as the actual shut of
the door against the seals, are important parts of
identifying an area where water can pass through.
Leak detection using ultrasonic equipment
When the vehicle is in motion, the body shape may
produce eddy currents and turbulence which can
force air and water through the smallest orifice.
When the vehicle is stationary, it can be difficult
to reproduce these conditions to a realistic level.
The ultrasonic equipment works on the principle
of a transmitter creating ultrasonic waves which
penetrate the smallest orifice in the vehicle body
and are then picked up by a receiver fitted with
a suitable probe, which can in turn pinpoint the
exact leak point. The transmitter is placed in a base
plate which automatically switches it on via a
reed switch in the base of the transmitting body.
Ultrasonic waves will then penetrate out through
the unsealed area, including the front windscreen,
wiper spindle and washer jet fitment, roof seams,
bulkhead seams and grommets, A-post area, door
seals, front wheel arch seams and heater air
intakes, to the receiver.
An important feature of this equipment is the
incorporation of a sensitivity control which enables
the operator to check a wide range of fitments. For
example, a boot seal is a very light touch seal,
whereas a urethane screen fitment is at the other end
of the scale setting of the equipment and would need
a high setting to determine a leak.
To ensure satisfactory leak location and testing,
it is recommended not to use a leak detector on a
wet vehicle, which should be blown dry prior to
the test. As with any equipment it is important to
read the instructions to enable the equipment to be
used to its full potential.
Sealing
Having located the point of entry of the water, it is
then necessary to carry out satisfactory rectification.
Door aperture seals and weather strips should
be renewed if damaged or suffering from deterioration.
Alternatively the seals can be adjusted by
carefully setting the mounting flange after making
sure the fit of the door is correct.
Leaks through body seams should be sealed from
the outside wherever possible to ensure water is
excluded from the seam. First dry out with compressed
air or a hot air blower.
When leaks occur between a screen glass and
the weather strip, or in the case of direct glazing
between the glass and the body, avoid removing the
glass if possible. Use recommended sealers to seal
between the glass and the weather strip or the body.
If the vehicle is wet then it should be blown dry
prior to sealing. It is difficult to seal a wet vehicle
because, if a fault is found, it cannot be rectified
quickly before moving to another area.
14.4.11 Windscreen repair: Glass-Weld
Pro-Vac
This system of repair involves extracting all the air
from the damaged glass and replacing the void
with a resin which, when cured with ultraviolet
light, is optically clear and is stronger than the
glass that has been replaced. The system is widely
accepted, and repair to Glas-Weld standard would
472Repair of Vehicle Bodies
not cause the vehicle to fail the statutory Department
of Transport test for windscreens: 80 per cent
of stone damaged windscreens can be repaired by
this method (Figure 14.111).
When glass breaks, an air gap opens up. Some
times crushed glass may also be present. There are
also flat surfaces present inside the glass on either
side of the air gap. These three things result in the
visibility of the damaged area being affected. The
damage will eventually spread further as the temperature
changes and the vehicle flexes in normal
use (Figure 14.112).
The system works, as follows:
1 All foreign materials and crushed glass are
carefully removed from the centre of the damaged
area to open up an airway into the break.
Certain types of damage may need to be precision
drilled (Figure 14.113).
2 The patent Pro-Vac injector is filled with the
appropriate resin, depending on local temperature
and humidity, before being mounted on the
screen. The injector is then threaded through
the stand until the outer seal makes airtight
contact with the screen (Figure 14.114).
3 The Pro-Vac injector is capable of creating a
total vacuum within the damaged area, which
is essential for top quality repairs. Using alternating
vacuum and pressure cycles, all of the
air in the break is withdrawn and the void is
filled with resin. Once the damage is optically
clear, curing can commence.
4 Using a special ultraviolet lamp, the resin is
cured. Once the curing process is complete the
repair area is not only optically clear but also
structurally sound; in fact it is stronger than the
glass it replaces (Figure 14.115).