Cracked Windscreen: MOT Failure or Not?

Will a Cracked Windscreen Fail an MOT? Understanding the Rules

The MOT test is a crucial annual check designed to ensure your vehicle is roadworthy and safe. One of the most common concerns drivers have regarding their MOT is the condition of their windscreen. A small chip or a long crack can leave you wondering: will this cause my car to fail its MOT? The answer, as with many things in automotive regulation, is nuanced. It's not simply a case of 'any crack equals a fail'. Instead, the severity and location of the damage are key factors.

This article will delve into the specifics of MOT windscreen regulations, explaining what types of damage are permissible and which will undoubtedly lead to a failed test. We'll cover the guidelines set out by the Driver and Vehicle Standards Agency (DVSA), the governing body for MOT tests in the UK, and provide practical advice for car owners.

The DVSA's Stance on Windscreen Damage

The DVSA has clear guidelines on windscreen condition for MOT purposes. The primary concern is driver visibility. Any damage that obstructs or impairs the driver's view of the road is a potential MOT failure item. This isn't just about a clear line of sight; it also encompasses distortions that could be mistaken for hazards.

The regulations focus on two main areas: the size of the damaged area and its location on the windscreen. Let's break these down:

1. Size and Type of Damage

The DVSA categorises windscreen damage into chips and cracks. While both can be problematic, the rules differ slightly:

• Chips: A chip is defined as damage where a small piece of glass has been removed. For an MOT failure, a chip must be larger than 10mm in diameter.
• Cracks: Cracks are more extensive than chips. The critical factor for cracks is their length and how they spread. A crack that is longer than 10mm is generally considered a failure. Furthermore, cracks that extend to the edge of the windscreen are also likely to cause a fail, regardless of their length within the main swept area.

2. Location, Location, Location!

The position of the damage on the windscreen is arguably the most significant factor. The DVSA divides the windscreen into specific zones:

• The "Driver's Field of Vision": This is the most critical area. It's defined as the area swept by the windscreen wipers, plus a further 8mm around this area. Any damage within this zone that is larger than a 10mm chip or a 10mm crack will result in an MOT failure. This is because it directly impacts the driver's ability to see the road clearly.
• The "Restricted Area": This is a larger zone encompassing the driver's field of vision, extending to the edges of the windscreen. Damage in this area, even if it doesn't directly impair the driver's primary view, can still cause a fail if it's a crack over 10mm long, or if it compromises the structural integrity of the glass.

When Does a Cracked Windscreen Fail an MOT?

Based on the DVSA guidelines, a cracked windscreen will typically fail an MOT if:

• The crack is longer than 10mm within the driver's field of vision.
• The crack extends to the edge of the windscreen.
• There are multiple cracks or chips that, combined, significantly impair visibility.
• The damage causes significant distortion or discolouration that affects the driver's view.
• The windscreen is shattered or extensively damaged, compromising its structural integrity.

What About Minor Chips and Scratches?

As mentioned, not all damage leads to a fail. Minor chips, smaller than 10mm, that are outside the driver's primary field of vision are usually acceptable. Similarly, very fine, hairline cracks that do not extend into the critical viewing area and are less than 10mm might pass. However, it's always best to err on the side of caution.

The discussion in the provided text highlights a common query: can minor scratches be repaired? While products exist to polish out scratches on items like camera lenses or even aquarium glass, their effectiveness and suitability for vehicle windscreens are questionable. As one user noted, such products might be expensive and not withstand the elements. Another user mentioned "jewellers rouge," a polishing compound, but its application to a car windscreen to fix a scratch is unlikely to be a viable or legal repair for MOT purposes. The key is that any repair must restore the glass to a condition that does not impair visibility. Attempting DIY repairs with unapproved methods could lead to a fail or even be illegal.

Can a Cracked Windscreen Be Repaired?

Yes, in many cases, minor windscreen damage can be repaired. Professional windscreen repair services can often fix chips and small cracks, restoring the strength and clarity of the glass. This is a far more reliable solution than attempting a DIY polish.

Windscreen repair typically involves injecting a special resin into the damaged area. This resin is then cured, bonding the glass and preventing the crack from spreading. For minor chips (usually less than 25mm in diameter) and short cracks (less than 150mm long), a repair can be a cost-effective and effective alternative to a full replacement.

Benefits of windscreen repair:

• Cost-effective: Cheaper than a full windscreen replacement.
• Prevents further damage: Stops cracks from spreading.
• Maintains structural integrity: Restores the windscreen's strength.
• Improves visibility: Can make minor damage almost disappear.
• Environmentally friendly: Reduces waste compared to replacement.

When is Replacement Necessary?

If the damage is too extensive or in a critical location, a full windscreen replacement will be necessary. This includes:

• Damage within the driver's direct line of sight that cannot be effectively repaired.
• Cracks longer than 150mm.
• Damage that has penetrated both layers of the laminated glass.
• Damage that affects the vehicle's safety systems, such as rain sensors or cameras integrated into the windscreen.

What to Do If Your Windscreen is Damaged

If you discover damage to your windscreen, it's wise to address it promptly. Don't wait until your MOT is due.

1. Assess the Damage: Determine the size and location of the chip or crack.
2. Consult a Professional: Visit a reputable windscreen repair specialist. They can advise whether a repair is feasible or if a replacement is required.
3. Check Your Insurance: Many comprehensive car insurance policies include windscreen cover, often with a low or zero excess for repairs.
4. Get it Fixed: If a repair is possible, have it done. If a replacement is needed, get it done before your MOT test.

A Comparative Look: Repair vs. Replacement

Here's a quick comparison to help you decide:

Frequently Asked Questions (FAQs)

Q1: My windscreen has a small chip, but it's not in my direct line of sight. Will it fail the MOT?
It depends on the size. If the chip is smaller than 10mm and not in the driver's primary field of vision (the area swept by wipers plus 8mm around it), it should be acceptable. However, if it's larger or closer to the critical area, it might fail.

Q2: I have a crack that is about 15cm long. Will this fail the MOT?
Yes, generally a crack longer than 10mm within the swept area, or any crack extending to the edge of the windscreen, will cause a failure.

Q3: Can I use a DIY repair kit on my windscreen?
While DIY kits exist, they are often not as effective as professional repairs and may not meet MOT standards. It's always recommended to use a professional service for the best results and to ensure compliance.

Q4: My car has advanced driver-assistance systems (ADAS) like lane assist. Will windscreen damage affect these?
Yes, many ADAS systems rely on cameras mounted on the windscreen. Damage in the vicinity of these cameras, or even a poorly executed repair, can affect their calibration and performance, potentially leading to an MOT failure or malfunction of the systems.

Q5: How can I check if my windscreen damage is likely to fail the MOT?
Refer to the DVSA guidelines on windscreen damage. The key factors are the size (over 10mm for chips, over 10mm for cracks) and the location (within the driver's field of vision). If in doubt, get a professional opinion.

Conclusion: Prioritise Visibility and Safety

A cracked or chipped windscreen is more than just an aesthetic issue; it's a safety concern that can lead to an MOT failure. The DVSA's regulations are designed to ensure that your view of the road is unobstructed. Understanding the rules regarding the size and location of damage is crucial. If you have any doubt about your windscreen's condition, it's always best to seek professional advice and have any damage repaired or the windscreen replaced before your MOT test. This proactive approach will save you time, money, and ensure your vehicle is safe to drive.

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