Paint it Black

 

 

A question often asked amongst motoring enthusiasts is, “I’m having my windscreen replaced today. Is there anything to look out for?” Generally, the advice will be pretty good, and mostly based on experience. However some responses are the work of fiction; a fallacy; an internet fable.

“Before the fitter puts the new windscreen in, make sure he paints over the scratches with that black primer!”

Porsche 991 Windscreen Removal

Paintwork scratched by windscreen fitter.

This statement highlights an important issue, and just how easily vital information can be grossly misinterpreted and misrepresented. Three of the most used aftermarket polyurethane bonding systems used in the automotive glass replacement ( “AGR” ) industry in the UK are Betaseal (Dow Automotive) Dinitrol and Sika. All three are also used by vehicle manufacturers on the assembly lines all over the world. From their respective websites:

Dinitrol 530.

“Black, solvent based physical and chemical drying primer designed to prepare the cleaned automotive glasses and the flange for direct glazing. DINITROL 530 promotes the adhesion of the polyurethane sealer to the substrates, but also prevents the degradation of the polyurethane due to Ultra Violet radiation.”

Betaseal 43532

“BETASEAL 43532 primer is recommended for use as an adhesion promoter between BETASEAL™ urethane adhesives and automotive paint coatings”

Sika 206 G+P

“Sika® Primer-206 G+P is used to give improved adhesion in adhesive bonding applications on sub-strates 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.”

The product descriptions are condensed, and a fuller technical data sheet furnishes us with all the finer details, but notwithstanding, the single paragraphs – at a glance – tell you what you need to know. The common denominator in all three: black primer is an adhesion promoter. Applying it provides a suitable substrate to bond to. There is no mention of it being suitable for coating bare, or bared,  metal. The emphasis of its use – by its users – is largely misplaced, and anyone using black primer – adhesion promoter – to paint over scratches is missing the point: avoid scratching the paintwork to begin with. The long term damage can be very expensive and often does not manifest itself until the car has moved on to a new owner.

BMW E46 M3 Windscreen

BMW E46 M3 Windscreen Removed

None of us are exempt from making an innocent mistake, but when we do, we learn from it; we gain knowledge. Experience is knowing all the pitfalls of your trade and more importantly, how to avoid them. We don’t paint the mistakes black with primer. We consciously avoid making those blunders in the first place. The prevention is a critical part of eliminating the risk of corrosion. Like in the image of the BMW E46 M3 above, sometimes there is no excuse to scratch the pinchweld on removing the windscreen and there is no justification whatsoever for the pinchweld to be bared of its paint when cutting back the old Polyurethane ( “PUR” ). Steve Allard of Western Windscreens in Launceston shows us just how futile covering a scratch with black primer really is. The car: a Mercedes-Benz SLK had come into his workshop for a new windscreen. It should have been a routine replacement, but the job turned into much more when he found some scratches which had been hidden with something that was not designed to protect bare metal from oxidising.

Merc Windscreen

Picture courtesy of Western Winsdcreens in Launceston.

Nobody in their right mind could claim the car is a rot box as the metal around the scratch has not rusted, therefore negating the claim or suggestion. The black primer is clearly not sufficient, and does not inhibit the corrosion of the metal beneath the paint.

Merc Windshield

Image courtesy of Steve Allard, Western Windscreens, Cornwall

Black primer is not for painting scratches. Its use is for preparing a freshly painted surface to promote better adhesion; it is used to provide a better a substrate to bond to; it is not designed to be used as a rust inhibitor, or to ‘fill in’ scratched paintwork. Even accident, or crash repair centres can be guilty of thinking that the windscreen fitter’s black primer is some magical cure, and an excuse for the painter not to put in the effort:
Windscreen Fail

Unsuitable for bonding

A Porsche 996 (pictured above) had a new roof skin replaced prior to the windscreen being removed after it cracked on a track day. Cutting back the PUR revealed some pretty alarming evidence of what was supposed to be a repair by a Porsche ‘approved’ bodyshop. There was evidence of black primer under the PUR but it had not adhered to the metal at all, and just lifted off the pinchweld like the floating thin layer of brittle black primer that it was. There was no chemical bond between to the two materials.

Those who are engaging in such practices will not be around to witness the damage in time to come. The car may even have since exchanged hands, and thus voided any warranty however subjective it may appear to be in the circumstances. The perpetrators of such careless and shoddy workmanship cannot be held culpable for the consequential loss which will invariably have been caused by their negligence, and this is as much of a crime as the act itself.

Removing a windscreen, and cutting back the adhesive that held it in is easier today than it has ever been. There are a variety of removal apparatus and cutting implements readily available whilst finely honed techniques remain the most important tool of the fitter’s repertoire. Yet there are so many who neglect to use them or are ignorant to the fact. In some ways, the windscreen fitter skills and mindset has perpetuated its own paradox. Added to this is an incessant need for speed; there appears to be so much emphasis on cheaper, easier and quicker ways to get the job done. Not many have the time nor the inclination to do a good job, or take pride in their work.

Windscreen Replacement

Appropriate and correct treatment of bare metal

It is inevitable that at some point, you are going to bare some metal as you cut back old PUR. It might be a raised spot-weld, or it might be a slip with your chisel. Within reason, and after careful assessment, you may be justified in ‘dotting’ a small mark in the bondline with primer, but if you want to be thorough, and offer a guarantee which is as robust as the work you’re aiming to complete, or is in line with the car manufacturer’s warranty, you have to spend a little bit more time than just dabbing on something which is not fit for purpose. A little more application – literally – is in order.
Windscreen Replacement

Treating bared metal with a chemically bonding agent

 

 

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Porsche 911 Windscreen: The 996

 

 

 

 

Headlights that looked like they were shaped from fried eggs, characterless exhaust notes and with an extremely soft suspension the Porsche 996 became known as the unloved series.

Porsche wrote in their 996 brochure, “Over the years we have broken with many conventions, but never with our principles. Therefore the new 911 is a direct result of more than 30 years of evolution..”  It was indeed larger, more comfortable, faster and quieter; signature 911 characteristics – developed and presented by Ferdinand Alexander Porsche – had been modified significantly, but some changes just didn’t sit right with fans of the marque. Despite this displeasure, figures made it the best-selling model in the car’s history marking the biggest turning point in the evolution of the 911.

The successor to the 993 did however inherit one common complaint in its genes. And as one frustrated owner once described,

“I have a really bad creaking noise coming from the dash board or lower front windscreen area on my 996 C4S. It sounds terrible!”

The 996 windscreen has, like its predecessor’s, been the subject of just as much fiction.

By design, the 993 and 996 windscreens are very similar. They both use a two-part trim: a frame or retainer (which fits around the glass edge) and a ‘covering frame’ which locks into it. The notable difference is twofold:

  1. The 996 trim frame is a shaped, one piece retainer which fits along two (left and right) sides and the top of the windscreen, also described as a ‘goalposts’ shape, whereas the 993 trim frame extends all around and encapsulates the entire windscreen perimeter. The second part of the ‘outer’ trim for both fits into both frames in the same way, similar to a tongue and groove joint.
  2.  During manufacture, the 993 windscreen has its trim frame enveloped under a bead of polyurethane. The 996’s trim retainer is a separate part and is fitted by hand, by the glass installer.

Both windscreens are directly glazed, i.e., they’re bonded (with an automotive grade polyurethane) to the car’s chassis. The similarities being so close suggest the cause of the creaking must therefore be the same. Well, the simple answer is yes, but in keeping with the theme thus far, it is, in different ways. The common denominator [in replaced windscreens] is usually installer error. With original, factory fitted windscreens it’s usually the aging – or degradation – of composite materials. Allowing for rare exceptions, the most common cause for any kind of creaking is movement. Two solid surfaces moving against each other will generate friction – a vibration – and voila!

At this point is also important to note that as much as there is a realistic possibility that plastics (and composite rubber materials) will be adversely affected by age and or exposure to extreme temperatures (or erratic temperature changes) there is not much evidence to support claims of product (or bond) failure. Polyurethane adhesives do not fail. People using them do. Most of the alleged ‘product failures’ are usually attributed to one, or a combination of the following:

  • inadequate surface preparation;
  • preparation in adverse or unsuitable weather conditions;
  • poor application of bonding materials;
  • contamination, or the presence of contaminants;
  • use of conflicting products thereby affecting the curing mechanism of the adhesive.

With the blame firmly pointing at the installer (also known as technician, engineer or fitter in different circles) the emphasis is placed very much on the process rather than the products. If the windscreen is set too high, as well as partially obscuring the VIN in the bottom right corner the trim frame will rub against the aperture and therefore generate a creaking or squeaking noise cue: the Infamous Helicopter Tape Myth. It’s great for protecting paintwork against scratches, and it will provide unparalleled abrasion and erosion resistance. How it made its way into 993 and 996 windscreen essentials remains a mystery. It does perversely, get a little bit of credit: it can be used as an insulating material against an audible vibration. Conversely, if a windscreen is fitted correctly so that no two surfaces are making contact with each other, the need to provide sound insulation is dispelled. Furthermore Helicopter or Teflon tape often introduces its own problems.

996 Windscreen2

996 Windscreen with infamous tape

Just like a lacquer or paint edge will peel, tape will also lift. It’s only a matter of time. Once it does, it can act as a dam trapping water and dirt behind it. I have removed and refitted countless creaking 993 and 996 windscreens, many of which had the ‘snake oil’ tape applied. Some of them did a thorough job of etching into the paint surface; others were just there doing nothing, looking like – and about as useful as – shedded snake skin.

Teflon tape windscreen

Shedded snake skin

In some cases, the paint had been scored (presumably where the tape had been trimmed with the blade of a scalpel). In terms of providing insulation against a creaking windscreen, tape works only when the windscreen has been fitted incorrectly. In fact, for what it achieves, you might as well wear ear defenders when you drive the car. The root cause of the creaking will still be there; the tape merely disguises it.

Trim Frame loose

Just add Neoprene chord

Another common issue comes when the trim frame (or trim retainer) separates from the glass. It’s something that will go unnoticed until you reach speeds in excess of 60mph and begin to hear what at first sounds like the noise a playing card would make against the spokes of a bicycle wheel (something all boys growing up in the seventies and eighties will identify with). Anyone hitting higher speeds (on a motorway or track for example) will hear what sounds like a radio controlled helicopter is hovering above the windscreen. A quick fix for this problem is to stuff a line (or two) of Neoprene chord; an ‘authentic’ Porsche part. Inserting the chord will simply keep the trim frame wedged against the glass edge. Paradoxically, in doing so, it simply treats the symptoms and is a long way from treating the cause. Ultimately, a new trim frame is required and this can only be fitted with the windscreen removed from the car.

996 windscreen

Adhesive on windscreen

Like the 993, the 996 windscreen leaves the manufacturer with a line of cured polyurethane applied to the glass. This is a true representation of the pattern required to install the windscreen correctly. It also acts as a buffer to aid setting of the windscreen to achieve the final and requisite position. Deviating from this mapped guide will affect the marriage of (cured and fresh) PUR, and can lead to creaking, wind noise or water ingress issues. The alignment needs to be true, and millimeter perfect. Get it wrong and there’s no recovering from it; you can’t backfill it, or make do. It will simply need to be taken back to the start and done again, correctly.

windscreen wind noise

Cause of wind noise

Check the trim around your 996; is it the correct type? If the windscreen has been replaced the installer may have used a one piece trim for fiscal reasons or in an act of complete incompetence. How can you tell? Simple: measure it. You may not even need to  as some of the trims I’ve seen used have included one for a Ford Transit which measures about 22mm in overall profile width, compared to the 15mm correct OE Porsche (assembled). In some cases, a wider trim (up to 27mm) is utilised to hide sins such as scratches, scuffs (inflicted during the removal process) paint defects, or even to conceal the presence of Helicopter Tape.

In summary, it’s not a difficult windscreen to fit. Conversely it is its simplicity which can lead to some very annoying – and often expensive – problems. Understanding the subject matter is key to achieving the best possible results. Using the same mindset as you would on an average windscreen in a fast-fit environment simply will not do. And whilst the adages and definitions of experience remain true, it’s more about attitude and application. The simple answer to why a 996 windscreen creaks could be construed as vague: it hasn’t been fitted correctly. Investigating the root cause still may not reveal a definitive diagnosis however, recognising one of the symptoms illustrated here will steer you towards the solution.

Do you have an issue with your 996 windscreen? Get in touch, especially if it is suffering from one of the issues highlighted in this post.