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Limits to Windscreen Repair Guarantees - Glasstec Paul

Can you guarantee a windscreen repair?

Broadly speaking, if there’s damage to glass you could argue that despite carrying out a good structural repair, aesthetically, glass cannot be restored to its pre-damage condition; there will always be some evidence. Whilst you can still state with a degree of confidence that a structural repair will probably not worsen, guaranteeing ‘already broken’ glass isn’t so straight forward. Cosmetic repairs are merely patch-up procedures to improve the appearance of a windscreen’s surface and do not present any uncertainty.

A cosmetic repair addresses damage to the surface of glass where impact damage has resulted in a scuff or shell. A structural repair can be the same impact damage but is much more complicated as it concerns the propagation of cracks in glass. The impact mark – or crater – is the ‘cosmetic’ part of the damage and cracks or shapes below the glass surface (behind the impact crater) is the structural damage and will require a different skill-set to address.

Provided the repairer is carrying out a thorough repair, where every part of the damage is ‘filled’ and restored (these are generic terms to make it easier to understand). Each crack will need to have repair resin manipulated to each tip of every crack emanating from the impact crater; every ‘bullseye’ or ‘cloverleaf’ will need to have any air and contaminants expelled before repair resin is induced. Only then can an assessment be made on the validity of a repair, thus, how guarantee-able it will be going forward. A correctly worked repair should not, and probably will not worsen. I’m using the word probably not because there is doubt, but it is never 100%. In the images above the repair looks almost perfect, and structurally is probably is; aesthetically it also looks to be, but despite the level of improvement, there is still some – albeit negligible – evidence of a repair.

A repairer with an in-depth knowledge and broad experience of repairing windscreens should be able to make a assessment on the likely outcome(s) of an attempted repair. An understanding of fracture mechanics and the basic physics of working with glass will enable a repairer to carry out a repair to his estimate of the outcome. That said, not all chips are equal; some are more complicated than others, requiring longer and more intricate repair techniques.

Can a chip ‘crack off’ during an attempted repair?

In short, yes. However, there are factors: ambient temperature (as well as that of the glass itself) the type of damage (and its position in relation to the glass edge). The complexity of a break is also critical as much as the proximity of it (to another break) is crucial. With the benefit of experience; knowing all the pitfalls of repairing chipped windscreens (and how to avoid them) there still is a degree of unpredictability around what could happen if you do not repair them, as much as what could happen if you do. There’s no rule of thumb regarding the weather and the cold snap making chipped windscreens more prone to cracking, or the increased temperature in the warmer months being a similar threat. It’s more to do with the juxtaposition of temperatures either side of the windscreen. In the winter you are likely to have hot air blowing against the inside of the windscreen (while the air outside is freezing). During the summer, the temperature inside the cabin is most probably cooled via the car’s air conditioning system resulting in a cool – or cold – inner layer of glass and the out layer of glass (in the sandwich construction windscreen) being hot enough to cook food upon. Again, these are factors which increase the likelihood of a chip extending to a crack, but not a hard and fast rule. Driving style and the terrain upon which the car is traveling (such as speed bumps) are also contributing factors. That said, I have offered to repair chips only to be told by the car owner that it has ‘been there for three years and hasn’t cracked yet’.

The equipment used in repair is probably as much of a consideration as the conditions in which to attempt a repair. There are two types: automated/mechanical pump assisted, or manual which is a totally human-controlled process. From beginning to end, the repairer must have the opportunity to intervene at any part of the process. The automated system somewhat restricts this autonomy as it is a preordained ‘1-2-3’ staged process (plus there is no access to the break should it need to be manipulated). Automated systems are capped in their ability to allow a repairer fully control the process. A manual system is controlled entirely by the repairer and allows the repairer to make any necessary adjustments during the key stages of the process. The success rate of the automated repair system is far from ideal too. Something in the region of 40% attempts do not end successfully. Compared to a manual system, the failure rate is less than 1%. A manual repair kit in the hands of an experienced repairer instills confidence as an assessment can be made on the most likely outcome of an attempt to repair; and with a failure rate of less than 1% the chances of a good, successful repair are extremely good. Conversely, using an automated repair system, a repairer might add a caveat as the chances of failure are far greater:

“If a windscreen chip we work on becomes a crack during our attempted repair, you will need a replacement windscreen. In that case you will have to pay any additional excess due for a replacement.”

– insurance approved repairer.

This may well reflect the different levels of experience of their employees but it doesn’t mean windscreens just crack for no reason:

“We do not guarantee each stone chip repair will be successful. Please note that we do not guarantee that an attempted repair to your windscreen will be successful in every case. Through no fault of our technicians, there is a risk of a crack appearing in the windscreen during the repair process and by ordering the Services from us, you acknowledge this risk. In the event that a crack does appear in the windscreen during the repair process, you may ask us to replace the windscreen for you. If we agree to do this, you will have to pay us an additional amount. We will notify you verbally of that additional charge before the replacement windscreen is fitted. If we are carrying out the Service through an insurance claim we will deduct any excess that you have already paid to us for the repair of the windscreen from this amount.”

– nationally operated repair company.

It is far more informative to be told why an attempt might crack rather than claiming it ‘might just do it’ through no fault of the technician:


“The visual appearance of a glass repair depends on the nature and severity of the damage to the glass at the time of the repair and there is no guarantee that a repair will be successful. Until the repair process is undertaken the results will be uncertain. If you are not happy with the visual appearance of the repair we can replace your windscreen at your cost.

“By agreeing to carry out a glass repair we do not guarantee that this will resolve the relevant problem, and in the absence of damage caused by our workmanship, any subsequent replacement of the repaired glass will be at your cost.

“In the course of a repair, the glass may crack beyond repair through no fault of our technicians. You accept that risk. If this happens we will ask you if you would like us to replace the glass. In these circumstances we will not charge you (or your insurers) for the repair, and we will take into account any excess, or other amounts, you have already paid to us for the glass repair by deducting these from the excess, or other amounts, payable for the glass replacement.”

– another repairer your insurance company wants you to trust.

The guarantee given on a repaired windscreen is based on an assessment made on that particular damage before an attempt is made. This is dependent on the factors explained and not because windscreens just decide to crack for no reason and at any given time. In short, equipment + experience + having the right amount of time to carry out a repair properly = a repair that you can most probably stand on.

How long will a a successfully repaired chip last?

Other than some age-related shrinkage and discoloration of the secondary resin (used to fill the impact crater) it can be argued that a properly repaired chip is stronger than the rest of the windscreen.

Prudent advice is not to sign a disclaimer, but discuss with the repairer what his or her estimate of the most likely outcome is. If the repairer’s default heading is, ‘they all do that’, or, ‘it will seal the hole’, you’ve got the answer you’re looking for.

Good luck out there! Please feel free to share your before and after images or even your repair experience.