Unskilled Windscreen Fitters



Many windscreen fitters say they’re experienced, but what kind of experience that really is will show in the end product or in the way they do their job. A windscreen fitter can be judged on how he or she fits a windscreen.

Bonded windscreens: applying the adhesive. 

How Wide?

Compressed, the Polyurethane adhesive (PUR) bead wall usually (should) end up about 10-15mm wide. This can be achieved using a trim and (or) appropriate spacers/paking blocks/bump stops dependent on the application. A ‘V’ shaped cut in the nozzle (of the extruder) will stand the bead up to about 12mm but this is variable depending on the regulation of extrustion, angle of extruder (it should be perpendicular, to the substrate BTW) and generally the combination of the aforementioned togethered with the speed in which you get the whole thing around the glass or frame to which it will be bonded.

BMW E36 Compact

Whoever fitted this BMW E36 Compact windscreen did not get any of that memo, obviously. There’s just no excuse for it.

Why should anyone be concerned about this? There are some technical details which I’ll spare (unless anyone really wants to know) but at some point in the car’s timeline the windscreeb will need replacing, and to do that someone has to come along and cut this windscreen out. And when, in your mind, you think the job will only take you *so* long, and it ends up taking twice as long because Mr Numpy Balloonhead stood the bead up as high as a prison wall, then squashed it down by pushing the windscreen FLAT against the pinchweld leaving barely a millimeter of PUR sandwiched between the two surfaces, your opinion of some [alleged] windscreen fitters is reinforced.

A few sweary words were shouted during the removal of this windscreen.

All this fitter had to do was give a flying proverbial. it would have been easier to whack a couple of rubber blocks against the bead to allow the windscreen to bed evenly.


Helping You Understand the Ballocks and the Bullshit


Have you had your windscreen repaired recently? How did the attempt turn out? Was the repair good, bad or indifferent? Were you confused about what you were told (by the repairer) at any stage? If you were, the chances are you had the wool pulled over your eyes.


Excuses for Poor Workmanship.



“Please understand: The largest misconception regarding chips is that they will disappear once repair has been done on the chip. The sole purpose of a stone chip repair is to maintain the structural integrity of the windscreen. Any aesthetic improvements are considered a bonus.”


Take a moment to comprehend what the message conveys.  The first part of the statement is true; repaired chips (or cracks) don’t disappear. There will always be some evidence of the repair. It’s not magic. How much you can see after the attempt to repair usually indicates how good – or not – the repairer is. The rest of the statement makes no sense, “The sole purpose of a chip repair is to maintain the structural integrity of the windscreen”. This sounds very technical and anyone with a damaged windscreen would be sitting up and taking notice. However all of this is undone with the closing line: “any aesthetic improvements are considered a bonus”.  In effect, you might as well say you rubbed your hand over the damage, so it should be fine. The very fact that there is a technical process in attempting to repair a damaged windscreen means, by definition, that there must be a discernible difference if that attempt is successful?

Some technical background to this is in order.

A windscreen repair technician should know how to repair a break , or what the likeliest outcome from his or her assessment of the damage. Understanding the science behind windscreen repair can help the repairer not only perform successful repairs but also educate their customers about the process instead of conning them of their money. Claiming that the break has been ‘filled’ or ‘sealed’ despite it looking the same after the process than it did before the technician started is probably the most common excuse. Most of these guys probably wouldn’t know what a good repair looks like never mind know how to go about achieving one


Preparing the Damage

To attempt a successful windscreen repair, you must rid the damage of air, contamination and moisture. Any loose debris must also be removed. This process alone debunks the ‘any aesthetic improvements are considered a bonus’ line, and shows how easily you can be fooled by someone purporting to know what they’re doing under their professional guise and pitch. The next step is to fill all areas of the break with resin. This may seem pretty straightforward, but it is not as simple as it sounds; to induce repair resin sufficiently requires different skills depending on the type of break. Time to ask Mr Aesthetic-Improvement-is-a-Bonus how to tell the difference between damage with resin in it and one without, perhaps?

Understanding the Break

There is usually an impact point although damage can still occur below the glass surface. This can be as small as a pinhead or a much larger impact crater which can extend from a couple of millimeters to way over the repairable limit (determined by the injector diameter). Behind the impact will be a circular shape (sometimes appearing to be dark or black) or a conal appearance in the glass. This is a basic cone – or part cone – damage and arguably the easiest to repair as most of the ‘bullseye’ or ‘half-moon’ appearance (if filled adequately) will be reduced to a slight watermark appearance once the process is complete. Small cracks or ‘legs’ radiating from the damage center form the more complex breaks and are generally more difficult to fill (and come with a slightly higher risk factor attached; the more legs, the greater the chance of one of them extending or cracking off). An experienced and properly trained repair technician will know how to manipulate the different types of damage in order to get the resin to flow (there are variables on this too). Irrespective of the type of damage you must remove any trapped air to allow the resin to flow. Ideally, you should remove any air from the break before any resin comes in contact with the damage. There are times that air must be drawn out during the repair; this has to be pulled through the resin by way of vacuum and pressure cycles (the force acting upon the air must be stronger than the surface tension of the resin in its way).

The Resin

The most important quality of a repair resin is its performance. First, the resin must be able to enter and reach all areas of the damage; product viscosity and by this, velocity (under applied pressure or vacuum). The cured resin should also have enough tensile strength to withstand any flexing, expansion or contraction that the windscreen may be subjected to.

Repair resin also needs to correspond to the same tensile strengths or have enough strength to withstand the expansion and contraction of the glass around it. Two characteristics make up the total tensile strength of the resin: adhesive strength and cohesive strength. Adhesive strength is the ability of the resin to adhere to the glass, and cohesive strength is the resin’s ability to hold itself together.

Another equally important characteristic is the resin’s refractive index after it has been cured. The refractive index determines how much a light wave ‘bends’ when entering and leaving the surface of the resin. Ideally, it should be the same as that of the windscreen, so that any light passing through the resin – and glass – acts the same as if it were passing through glass only. This makes the resin in the damage about almost invisible, upping the game from being considered a bonus as our friend suggests.

Curing the Resin

Resin cures as the result of a photochemical process in which monomers harden or cure upon exposure to ultraviolet radiation. A specifically formulated monomer will bond with other monomers – or polymerize – when it is exposed to UV light and isolated from oxygen molecules. This UV ‘curable’ monomer has a photo initiator which absorbs UV energy and initiates a polymerizing reaction in the monomer. In order for this reaction to take place, the UV radiation must be in the correct wavelength (usually 365 to 380 nanometers) and be of sufficient intensity to completely polymerize the resin within a few minutes if not seconds when using a high powered lamp. Any aesthetic improvement is considered to be a bonus, or does he mean a fluke in his case?

As Far as Misconceptions Go…

While many claim that windscreen repair is not an exact science, the facts prove otherwise. In simple terms, if the damage looks the same after the attempt to repair it, it has not been repaired. Decades of research and development into what some people have even referred to as a black art confirms that anyone rolling out piss poor excuses and statements like the one above is insulting your intelligence. The aim of this post is to arm you with some basic facts so that you can challenge the bullshitters and if, as a result, you can use these to prove how your perfectly repairable windscreen has now been condemned as a result of incompetence, well, this in itself would be considered the real bonus.

Leaking Windscreens are NOT Covered.




A trade customer – an independent garage – had a car in for service. They were also asked to look at a water leak in the front of the vehicle which turned out to be a poorly fitted windscreen. Water was dripping into the cabin from above the rear view mirror. The garage called me in to remove and refit the windscreen.

After a quick pre-inspection, there was also another problem: the windscreen itself was delaminating and was showing severe separation (of the sandwich construction). The glass was also extremely brittle (light pressure on the outer layer was displacing water from within the glass and PVB layers). Whilst the successful removal and refitting of the windscreen was still viable to eliminate the leaking issue, the glass itself was not fit for purpose, and thus unsuitable for reuse. A recommendation that glass should be replaced was relayed back to the vehicle owner.

The car owner contacted his insurer and explained that his car had a leaking windscreen. He claimed that they (the underwriters) were sympathetic and said they would ‘honor’ him with a new windscreen in the circumstances. Unless he has something exclusively written into his policy which covers him for the poor workmanship of a previous windscreen installer (before or during his ownership) leaky windscreens are not construed as damage, and therefore, not covered.

The following day the garage called to let me know that the windscreen was about to be replaced by the car owner’s insurer (or their nominated repairer).

My guess is that the call (from the car owner) to the insurance company would have been diverted to the nominated repairer. If the owner did state that the windscreen is leaking, is the repairer acting fraudulently? Was the onus more on the owner not to initiate contact with his insurer for an issue for which he was not entitled to be indemnified? Or was the insurer negligent?
On paper, the car owner got a new windscreen (worth well over £700) and the repairer delivered according to their service level agreement. However, the windscreen was not damaged. It was leaking. Leaking windscreens are not classed as damage, and therefore not covered by insurance.

Who’s to blame in this instance?

(Insurer’s name, the car owner’s name and the VRN have not been revealed to avoid litigation).

The Cost of Someone Else Paying Your Excess




Insurance companies implemented a policy excess system in order to deter gratuitous claims. However now there is a culture which could be using this deterrent to encourage the very thing it was designed to curb.

How somebody else paying your excess could be costing you.

In insurance, the policyholder contribution, or the ‘excess’, is the amount you have to pay if you make a claim. Without an excess, claims would increase dramatically and, ultimately, the cost of insurance would rise. It is a studious measure to deter people from making frivolous or unnecessary claims for minimal damage which would, invariably, inflate the cost of insurance. It is also helps to prevent fraudulent claims. This article focuses on that small, yet significant aspect of car windscreen (and glass) claims: the excess.

Who pays?

Windscreen Excess Amount

Cash Notes

In a nutshell, a windscreen repairer offering to pay your excess is vying for your business. By offering to cover a policyholder’s contribution, they are trying to attract custom, plain and simple. However, given that the average excess amount is circa £75.00, the amount would seem too great to write off; it would need a claw-back somewhere, surely. Where does the buck stop? If the billing is carte blanch, the repairer might simply add the ‘waived’ amount to the final invoice before billing the insurer. There may even be some creative billing whereby fictitious constituent clips, peripheral parts or out of hours charges will be added to cover the shortfall created by offering the insured party a freebie. Some busier (or even desperate) repair companies may even absorb the impact based on either the volume of work this kind of marketing might be generating, or that it is seen as something doing (and better than standing around scratching their proverbials). Whichever way you want to look at it, or any business attempts to justify it, knocking off around 50-quid distorts the market and ultimately alters the true value of repairing or replacing a windscreen. Per contra, windscreen repair and replacement companies are not the only culprits of this perfidious practice.

Secondhand car sellers.

Selling a car with a damaged windscreen or poorly repaired stonechip could prove to be a deal breaker. It may also take a huge chunk out of the seller’s profit margin as the cost is usually not covered by their car trader policy. Some sellers for example will offer a £50.00 discount suggesting that the buyer could claim for a new windscreen on their insurance after buying and subsequently insuring the vehicle. Others might even promise to pay the excess when – or if – the windscreen is (eventually) replaced. Of course, morality aside, to initiate an insurance claim for damage which occurred before policy inception is tantamount to fraud. The system however, is open to this kind of abuse and much of this type of activity goes on undetected.

Overall, the motor insurance industry is extremely competitive; motor insurance providers are relying more and more on high volume sales which in turn enables them to offer cheaper rates to the consumer. Conversely, every change in an individual’s circumstances will have a bearing on the cost of their insurance; age, car type; postcode, usage, where the car is kept; previous claims; driving convictions and more. These are all significant factors in calculating the cost of insuring motorists. An increase in the number of claims made will also be collated to profile different motorists, and calculate the risk of insuring them based on that data.

Is your claim necessary? If it is, ask yourself what the overall implications would be if someone was distorting the claim amount for their own gain. It would be incredibly short sighted to satisfy your thinking if the answer was for fiscal reasons. If you are saving the excess payment; the repairer is gaining the claim amount, and the insurer ultimately is indemnifying the loss, there can be no complaints when there is a premium hike when the policy lapses. Now rethink the previous statement in reverse. Is the insurer subsidising a transaction?

Ask yourself, would you still be making the claim if you were paying the excess yourself? Better still, ask the repairer why they would ‘lose’ or waive a significant part of the final bill in replacing a broken windscreen. If you’re not paying, who does?


Wrong Windscreen Fitted to Car.




Some things are not seen as a problem until they affect us directly. Try to imagine how you would feel if, after buying the car you’ve coveted for a while springs a very wet surprise as you drive through the rain for the first time: a leaking windscreen.

If the car came with a guarantee, the issue will be addressed; but what if it didn’t? What if it has lapsed? What if the warranty does not cover glass and seals? Or perhaps the previous keeper had the windscreen replaced at some point during their ownership, and the guarantee – as it usually is in most cases – ended when the car was sold. Whatever it is, someone is going to have to take the hit; fast forward: remove and refit the windscreen. And this is where the problem goes from bad to worse. Much worse.

The windscreen is removed, and the leak is attributed to poor workmanship by whoever fitted it previously. However, on removing the glass, something doesn’t look right. It’s the headlining; it’s not straight, and looks like there’s something ‘bulging’ between it, and the roof (there is also a rounded cut-out to one side of it on the leading edge).

Wrong Windscreen

What’s this, hidden by the previous installer?


Further investigation revealed what appeared to be the end of a wiring loom.

Wiring for windscreen rain sensor

Wiring for windscreen rain sensor

There were in fact, two multiplugs stuffed behind the headlining. At this point, it still did not suggest anything sinister. After all, many car manufacturers will install every car with one ‘fits all’ wiring loom but not the features it supplies (which may be variable options between different models). These two plugs suggest at least a rain sensor and possibly for a photochromic – or self dimming – rear view mirror). One way would be to plug into the car’s computer to see if there is a fault showing as a code on the system. Or, a quick glance at the car itself might tell its own story.

Windscreen Auto Lights Sensor

Auto Lights Option

The ‘auto’ lights setting on the switch all but confirms that the car should have a different windscreen to the one fitted.

Automatic Wiper Control

Auto Wipers

Affirmative. The car is definitely equipped with an auto lights-on feature, as well as a rain sensor. However, and unfortunately for the current owner, the windscreen itself does not correspond with this criteria.

No Rain Sensor Mounting

No Rain Sensor Mounting

The image above shows a basic mirror mounting plate (or boss). The ribbon, or tab above it is the ground for the heater elements within the windscreen (heated windscreen) and the break in the line cutting below it is the reason this windscreen was letting in water. A very awkward conversation ensues with the car owner, “Would you like to hear the good news first, or the bad?”

At this point, two questions beg to be answered:

1. How – or why – did this happen? It could be that the previous installer had the wrong windscreen and simply took a chance by decommissioning (and defenestrating) the ancillary device(s). In this example, something a bit more contrived appears to have taken place as the mirror is the correct one (perhaps this car was de-fleeted stock, or at a car hire company and the installer simply raided other cars for the mirror, or even took it from his own van!).

In some cases, the unscrupulous types may have even fitted a cheaper windscreen (cheaper than what the correct screen the insurance company – for example – thought they were paying for).

2. Who pays to put it right? The recommendation is not to refit this windscreen; it’s not the right one for the car and besides, the car’s computer would have registered faults after self-diagnosing that components are missing and wiring has gone open circuit. The windscreen remains ‘quarantined’ and the car has been declared VOR until it is rightfully decided who pays to replace the missing parts.

Your views please.


Botched Windscreen Repair.



Yet another example of the level of incompetence which is rife in windscreen repair. And it’s not rare to see such poor standards. In this instance, the act is nothing but a con.

From a customer, via email:

“He used a heat gun, and it looked alright when I signed it off but when I got in the car later it looked so much worse.”





He also says it looks worse now than it did before the insurance nominated windscreen repairer’s technician ‘attempted’ to repair it. His insurer would have been billed for it after he was duped into signing the repairer’s job-sheet. The job-sheet, signed whilst the screen was still hot, is a common trick used by many in the trade. Is it ignorance, or negligence? And who to blame, the employee or the employer?

VW Golf R32 Windscreen Replacement



You’ve gone through the car with a fine tooth comb and it’s faultless; the HPI report comes back all tickety boo and you exchange money for the keys – and V5 – before hitting the road home. It’s your new pride and joy. But there’s something not quite right, and you won’t know just what that is until it shows up as a costly problem to fix.

Windscreen before removal

Windscreen before removal

Kicking a tyre won’t find a defect just as much as knocking on the windscreen reveal if it’s been replaced or not. Seeing a ‘VW’ logo merely tells you that the glass is a genuine part; it doesn’t tell you if it is the original factory fitted (OEM) one. In all fairness, if the car has a windscreen free of chips, cracks or scratches, the chances are you’ll spend more time looking through it, than at it. Your attention will not be drawn to the glass itself unless there’s a problem with it, and it’s the windscreen that can be hiding those potential issues. One of the most common, is damage caused by a careless windscreen fitter.

Windscreen Removed

Windscreen Removed

A widespread misconception about what the adhesion promoter (in a windscreen bonding kit) is that it is to ‘paint over any scratches’. Even the adhesive manufacturer technical data sheets do not state this, yet this mistaken advice is finding its way into many conversations, “make sure he paints over the scratches!” they will say. Bizarrely, not many people understand that not scratching the paintwork in the first instance is (obviously!) the correct approach. In the image above, it looks as though there’s just a bit of black paint on the paintwork. As innocuous as it might appear, experience has taught me that it is usually there to cover up a mistake. And it will go unnoticed, because the average windscreen fitter (from the cheap, cowboy independent to the ‘insurance approved’ uniformed ‘technician’ representing a national brand) will not see anything untoward about it. I used a fine Scotch-Brite hand pad, and gave it a bit of a tickle…

Black primer removed

Black primer removed

There are many polyurethane adhesives on the market, some are excellent and some are sold purely on being the cheapest on the market. Sika manufactures the best product I have used, and thus, the only PUR I have used in almost a decade. Quoting directly from their Product Data Sheet is a description of when and where the ‘black primer’ should be used:


Areas of Application
Sika® Primer-206 G+P is used to give improved adhesion in adhesive bonding applications on substrates such as glass, ceramic-coated glass and painted surfaces. Sika® Primer-206 G+P can also be used on other substrates such as plastics and some metals.
This product is suitable for experienced professional users only. Tests with actual substrates and conditions, especially boundary temperature conditions have to be performed to ensure adhesion and material compatibility.



It is not a rust inhibitor, and it certainly is not formulated to cover scratches and protect the metal exposed as a result poor workmanship. By using an appropriately sized chisel and with the correct technique, damage to the pinchweld and surrounding paintwork is minimal, if any at all. If any bare metal is exposed, an appropriate treatment process should be followed. Scratches are caused by carelessness, and the use of inappropriate tools such as long blades, Stanley Knife tools and surgically sharp chisels with removable blades.

Cutting Back PUR

Cutting Back PUR correctly

Rust remover treatments, etch-primers, paints and polishes have firmly become part of my tool kit over the recent years; the paint damaged cars (from previous installers) have become a very common problem to deal with on a day-to-day basis. In most cases this type of damage will go undetected until the windscreen (or body-glass) is removed.

Teatment Process

Treatment Process


This is not something that can be ignored with a shrug of the shoulders either; and only after any further corrosion is prevented the original task of replacing the cracked windscreen can be continued.

Ready for New Windscreen

Ready for New Windscreen




This carelessness – by the previous installer – added unnecessary time to this job. Shoddy workmanship is unfair on the next installer, and is unquestionably unfair on the car owner especially if it comes at an extra cost. It’s all preventable, and just taking a few extra minutes to do a tidy job can avoid hours of correction work. More images of the job can be found on the Glasstec Facebook page here.

New windscreen installed

New windscreen installed


If you have had the windscreen replaced on your Golf, and would like to discuss any issues with it, please use the comments box below.

A good related forum is R32OC.com where there is a thread running on the subject.