The Windscreens of Change




Most car owners would begin to feel nervous if the guy about to replace their windscreen set himself up with a couple of sharpened screwdrivers, a rubber mallet; a length of waxed sash chord; some paraffin and an old car tyre.

“When I started in this trade – 32 years ago – you didn’t need much more than this” says Steve Allard, boss of Western Windscreens. He started as a trainee fitter just as the windscreen replacement industry was about to experience one of the biggest changes it has seen to date. And just as the trade was sweeping up the remaining fragments of shattered glass, dusting itself off and licking its lips at the advent of laminated windscreens, the idea of glazing glass directly to the car landed from the future and took everybody by surprise, whether they liked it or not.

Windscreen Removed

Bonded Windscreen Vauxhall Insignia VXR

In an inherently reticent trade, making room for new technology was never going to be easy and would always take time to bed in. But as the cantankerously cautious were closing up their cantilever tool boxes in fear of such changes, the proactive were prudently embracing what is now one of the most important safety features of a motor vehicle: the bonded windscreen. Modern cars now feature larger ‘directly glazed’ panels which form part of a car’s safety features as well as providing better efficiency. To help achieve this, the sandwich construction of glass and Polyvinyl Butyral (PVB) is now thinner than previous examples; some of the metal hardware (to hold condensation, light and rain sensors; active lane assist and road sign recognition cameras, etc) has been substituted for lighter plastic components, and microns have been spared from applying a finer coat of – black, UV inhibiting – ceramic paint to the inside of the glass. As the motor car itself has continued to evolve, chromed embellishers and ‘lockable’ rubber gaskets have been phased out and replaced with clip-mounted mouldings or extruded trims (but now even they are slowly disappearing to give modern day glass a more flush and seamless look on a car). With this has also come the need for a more refreshed mindset for the auto-glazier, and an entirely different set of skills which has transformed the task of fitting glass into something far more technical, yet paradoxically easier.

Today there is a much wider range of specialist tools than what Steve cut his teeth on over 30 years ago. But some innovations (thankfully) didn’t last very long. Like the transformer needed to ‘cook’ a heat sealing ribbon – Solbit – is about as extinct as the cars it was once used on, and such bonding materials no longer need to be stored in refrigerators to keep them at optimum workable temperatures. The first windscreen-specific Polyurethane adhesives (PUR) would need to be heated in order to promote flow and workability but advancement in PUR technology has since waned that wave of temperature-sensitive bonding material.  Gone too are the associated setting times, or Safe Drive Away Times (SDAT) which have gradually diminished from as long as 24-hours to a relatively pit-stop time of 30 minutes (airbag dependent). 

Windscreen Adhesive

Heated Rear Window Vauxhall VXR8

As older cars move into classic and vintage categories, the tools (and techniques) needed to work on them are becoming just as niche. Specific clip-releasing equipment has pushed chrome embellisher insertion tools firmly to the back of the drawer; bashers and dibbers now gather more and more dust as the two-man-teams – the brute force and strength – have almost been out-muscled by mechanically assisted equipment. Piano wire, braided wire and short lengths of beaten copper pipe have become part of a long legacy as a much safer, square-profile wire is the preferred method of cutting through PUR to release bonded glass from the vehicle.  

For every improvement made on fitting glass and windscreens, the trade has also developed better techniques to remove them, and as aware as we have become about ‘structural stiffness’ and as educated as we are of ridding contact surfaces and substrates of contaminants, the industry is still learning.  These developments in skills; those innovations in technology, and this continuous improvement to integrate – and harness – them into a specialist trade has turned the windscreen fitter of yesteryear into the automotive glazing technician of today. This refreshing attitude towards awareness has seen an encouraging interest towards achieving accreditation and certifying competency even though there is still no requirement.

Bonded Windscreen and Glass Roof

Volvo V40 Panoramic Glass Roof

It is estimated that there are approximately 700 windscreen replacement businesses listed as wholesale customers in the UK, from local one-man-bands to corporate powerhouses employing hundreds of staff covering all corners of the United Kingdom. There are thousands of technicians gainfully employed, many of whom are registered with the IMI’s own ATA scheme, as well as the similar work-based NVQ awards. Although neither scheme is compulsory, conscientious technicians are still keen to grow with the industry; they understand there is direction in the practice of maintaining and developing skills and expanding the knowledge required in their chosen field.

In a business fueled by safety which, in itself drives the need for technological advancement,  the desire for slimmer, lighter and above all safely installed glass, means that we, as industry professionals, must stay on top of the latest changes at all times. Our customers deserve better than a badly fitted windscreen, poor execution and even poorer customer service. We must strive to achieve and of course deliver, the best at all times – and reach beyond that.

Problems with a Porsche 993 Windscreen

The Porsche 911 993 windscreen is one of the most uncomplicated and straight forward windscreens to fit, yet they can give you many problems if not done correctly.

The Problems

It’s fairly common knowledge that the two most prolific issues which arise from the windscreen, or windscreen area of the car, are corrosion of the aperture (or pinchweld) and a very irritating vibration – or creaking – noise. Conceding that the former could well be attributed to a design flaw, both problems are usually traceable to human negligence, especially if the car has had its windscreen replaced. To identify and illustrate what these problems are, and just how bad they can get, I have chosen this 1995 car on the basis of its age, condition and comprehensive service history.

The Car

This 993 is extremely ‘clean’ and looks to be a fantastic depreciation-proof investment.  A C4 coupe 6 speed manual, she’s flawlessly finished in a Polar Silver metallic paint with an unmarked – and as new – gray interior; hard backed leather sports seats to boot. The car has been well maintained and between just three former keepers every mile, every turned nut and bolt, has been meticulously accounted for. The current owner wanted to address two annoying problems which first began to surface a few months after he’d bought the car: corrosion (on the scuttle below the windscreen) and, “it sounds like the pitter patter of rain” he said.

NB: I have covered the VIN in order to concentrate on the subject, and not on the car or its identity.

The Evidence

Like with any windscreen replacement, most car owners will see the finished product; in most cases, they start with a damaged window and when the work’s done, they’re presented with shiny new screen. If there are any issues in the finish, sometimes they’re immediately obvious but some problems will not manifest themselves until later. One of the most annoying scenarios is finding such a problem as the new owner of the car. The story with this car started with such a sketch.

Porsche 911 993 Windscreen

Porsche 911 993 Windscreen

To be fair to the current owner, it’s an easy detail to overlook when looking over an otherwise fantastically maintained – and presented – car. “It was only until after I got it home and wondered if it should be like that,” he said “I decided not to query it as I was so pleased with the car”. Some six months into his ownership, his ear ‘tuned in’ to the infamous creaking noise and like many other Porsche owners, he put it down to a dry bush or guessed that it might be a tightness in the dashboard somewhere. The car subsequently ended up with a Porsche independent who immediately spotted the gap in the damming rubber, which prompted him to look for other telltale signs. On closer inspection, there was no doubting the windscreen had been replaced. Underneath the outer trim, or ‘sealing frame’ was not a pretty sight.

Poorly fitted Porsche windscreen

creaking windscreen

Please also note that there may have been approximately a year (or more) between spotting these issues and having them corrected; the bubbling paint was not as bad when first noticed.

My remit was to remove the windscreen so that the bodyshop guys can tackle the corrosion. The following pictures tell their own story.

Porsche 911 993 Windscreen Problem

Chassis view window painted over!

Creaking windscreen

Rust underneath poorly applied adhesive

The windscreen was removed – intact – and whilst it was difficult to ascertain if had been fitted from new (or removed and refitted) there was no mistaking the attempts to cover up a multitude of mistakes.

Windscreen woes

Chassis view window cover-up

Creaking windscreen

Excessive corrosion to pinchweld

The Work

Leaving the bodyshop guys to deal with the corrosion (which pointed towards some over zealous use of a knife by a previous installer) the windscreen needed some extensive correcting of its own before it would be ready for refitting. My suspicion is that for whatever reason, the windscreen had already been removed and refitted. This may have been in a bodyshop (for paint.corrosion correction) or possibly even to rectify a replacement problem such as creaking, leaking or wind noise.

The Clean Up

Windscreen Clean Up


Windscreen Cleaned


There was a lot of making good to be done and found hidden beneath the mess was one of the reasons why these windscreens creak: silicon contamination. In order to obtain a more flush-fitting finish, the 993 front screen comes, from the manufacturer, ‘pre-encapsulated’ within the trim frame (like the one on the heated rear window, this is not available as a separate part). The plastic-coated frame is slotted onto the glass and provides a groove for the outer (rubber) trim to lock into. With the trim frame around the perimeter, a bead of Polyurethane adhesive (PUR) is applied over the line where the trim frame meets the glass. The idea is to bond these two parts together and in doing so, provide a raised profile to which fresh PUR is applied when fitting the windscreen to the car. A mistake many make is to cut into this pre-applied PUR. In this case, there was little left of the factory-applied PUR; the silk-printed ceramic frit had been obliterated with black adhesion promoter and the trim frame was loose. Given how contaminated the substrate was, the best policy was to cut right back to the ceramic coating; much of what was left of the existing PUR simply peeled off.

Creaking Windscreen

Not good enough

The next steps were crucial. Nobody likes doing preparation work; it’s boring, it takes time and you cannot see an immediate result.  However, the importance of prepping the substrate sufficiently couldn’t be more important in this case. This screen was riddled with silicon and had to be removed before we did anything else.

Porsche Windscreen

Removing contaminant

Creaking Porsche Windscreen

Clean as a whistle

With the contact surface neutralised, work began on getting the trim frame back on and bonded under fresh adhsive. There are a couple of points which I am purposely omitting at this stage under the banner of trade secrets but mainly because this is a very involved remove and refit of a 993 screen and that those particular details would probably not apply to the fitting of a new screen.

Creaking Windscreen

Trim Frame fitted and fresh PUR adhesive applied

With the fresh PUR applied, the windscreen is left in a cool, dry room to allow the adhesive to cure through to its core (brand, temperature and humidity dependent, this could take up to 84 hours). For your information, I use a Sika AGR OEM Approved PUR adhesive system. Once the PUR has cured, some trimming may be required to allow the screen to sit at the required height.

The Repainted Car

From the moment the fresh paint has been baked, the car must be allowed to cool down for 24 hours after it is removed from the oven. This is part of the paint curing process. Sika recommends a bonding process specifically for freshly painted cars and this process is followed according to their guidelines.

Creaking Windscreen Cure

Fresh Paint

993 Windscreen

Adhesion promoter applied

With the inner damming rubber in place, there are some minor adjustments to be made before the windscreen can be bonded back into place. These tweaks are made from ‘dry’ fitting the screen and ascertaining the where correct position is in relation to where – and how – the screen will sit on freshly applied PUR. Some final preparation touches are made before setting the screen into position. And she’s in:

Creaking Windscreen

View from inside – antenna no longer visible.

The final step is to make sure this problem doesn’t creep back in years to come.

And Finally

Some shots of the finished job.

Porsche 911 Windscreen993 Windscreen

Windscreen Porsche

993 C4S Windscreen Remove and Refit: Done.

I invite, and welcome your comments.