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).