What Causes Windscreen Cracks? Common Reasons & Prevention Tips

A cracked windscreen doesn’t start as a major problem, but it can turn into one if ignored. Small chips may seem harmless at first, but they can spread due to temperature changes, road vibrations, and even minor pressure. In Australia, where roads are often exposed to extreme heat and sudden weather shifts, windscreen damage is a common issue. Above all, most of these windscreen replacements could have been avoided if minor chips were repaired on time. Cracks weaken the structural integrity of the glass, increasing the risk of shattering during an accident.



Understanding why windscreens crack and how to prevent further damage can save you from unexpected expenses and safety risks. This guide covers the most common windscreen crack causes and practical prevention tips to help you avoid costly repairs.

A cracked windscreen doesn’t happen without a cause. Everyday driving conditions, unexpected weather changes, and even small driving habits can weaken your windscreen. What starts as a tiny chip can quickly expand into a long crack, often requiring a full windscreen replacement if ignored. Understanding what causes windscreen cracks is essential to preventing expensive repairs and ensuring your safety on the road. Below are the most common reasons behind windscreen cracks and proven ways to prevent them.

1. Road Debris & Flying Stones

Driving behind trucks or on unsealed roads significantly increases the risk of road debris windscreen damage. Small rocks, loose gravel, or even metal fragments kicked up by fast-moving vehicles can hit the glass at high speeds, causing immediate chips or cracks. At 100 km/h, a tiny stone the size of a pea can strike with enough force to leave a bullseye crack on your windscreen. If the glass already has micro-fractures from previous impacts, even a small pebble can trigger rapid crack expansion.

How To Prevent It

• Keep a Safe Distance – Stay at least three car lengths behind large trucks and vehicles carrying loose materials.
• Avoid Unsealed Roads – Roads under construction or covered in gravel increase the likelihood of windscreen chip vs crack issues.
• Use a Windscreen Protection Film – This adds a layer of protection to absorb minor impacts from debris.

2. Sudden Temperature Changes & Weather Conditions

Extreme heat and sudden cold snaps can lead to temperature changes and windscreen cracks. The windshield expands in hot weather and contracts in cold conditions. If this shift happens too quickly, stress fractures form, weakening the glass. Pouring hot water on an icy windscreen or turning the A/C to full blast on a hot day can shock the glass, causing small cracks to form or existing ones to spread. Laminated windscreens expand at different rates, making them more vulnerable to thermal stress.

How To Prevent It

• Avoid Rapid Temperature Changes – Gradually adjust heating or cooling settings inside your car.
• Park in the Shade or Indoors – Protect your windscreen from direct sunlight and frost buildup.
• Use a Windscreen Cover in Winter – Prevents frost accumulation, eliminating the need for hot water defrosting.

3. Poor Windscreen Installation & Structural Weakness

A poorly installed windscreen is prone to stress fractures due to uneven pressure distribution. Over time, even small vibrations from daily driving can cause the glass to shift, leading to structural cracks. A bad windscreen installation often results in gaps in the seal, allowing moisture and dirt to seep in, further weakening the glass. Common signs of a poor installation include wind noise at high speeds, visible warping, or improper alignment.

How To Prevent It

• Only Use Certified Professionals – A correctly installed windscreen ensures durability and prevents stress fractures in windscreen.
• Check for Proper Fitment – No visible gaps, uneven edges, or loose seals.
• Ask About Adhesive Curing Time – Avoid driving immediately after replacement to allow proper bonding.

4. Slamming Doors & High-Pressure Impact

Many drivers don’t realize that slamming the car door can cause pressure cracks windscreen issues. Every time a door is shut forcefully, air pressure inside the cabin increases, pushing outward against the windscreen. If there’s already a minor chip, this extra pressure can cause it to spread rapidly. Heavy objects, like a toolbox resting against the windscreen, also put continuous stress on the glass, leading to micro-fractures.

How to prevent it

• Close Doors Gently – Avoid unnecessary shockwaves that stress the glass.
• Check for Existing Chips Before Applying Pressure – Even placing a GPS mount on a damaged area can worsen cracks.
• Avoid Resting Heavy Items on the Windscreen – Extra weight can magnify pressure stress.

5. Hailstorms & Natural Disasters

In Australia, hailstorms are a major cause of hail damage windscreen cracks. Unlike regular debris, hailstones fall from great heights at high speeds, creating starburst cracks or even completely shattering the glass. Even small hailstones at 80 km/h can cause impact fractures, and larger hailstones (over 5 cm in diameter) often result in windscreen replacement rather than repair.

How to prevent it

• Park in a Garage or Covered Area – Always check the weather forecast if parking outside for extended periods.
• Use a Hail Protection Cover – Specially designed covers absorb impact from falling ice.
• If Caught in a Storm, Find Shelter – Stop under a bridge, gas station canopy, or indoor parking structure.

A small windscreen chip might not seem urgent, but waiting too long can lead to a full-length crack, making windscreen chip repair impossible. Temperature fluctuations, road vibrations, and pressure changes put constant stress on the glass, causing minor damage to spread faster than expected. But once a crack forms, it can grow unpredictably, depending on factors such as:

• Crack Type – Star cracks and long cracks are more likely to spread than small bullseye chips.
• Glass Stress Points – Cracks near the edge of the windscreen weaken the structure faster.
• Driving Conditions – Bumpy roads, heavy braking, and door slamming accelerate crack expansion.
  

But there are some techniques that you can utilize to stop a windscreen crack from spreading and avoid an expensive windscreen replacement, that have been explained here.

1. Act Immediately Before the Crack Spreads

If you’re wondering, “Can a windscreen crack be repaired?”, the answer depends on how quickly you take action. Small chips (less than a coin’s size) can be repaired if addressed early, but delaying the fix can allow dirt and moisture to enter the crack, making it harder to repair.

• Cover the crack with clear tape to prevent dirt and moisture from making the damage worse before repair.
• Avoid washing the car with high-pressure water, as it can force contaminants into the crack.
• Minimize driving on rough roads, as vibrations can cause the crack to grow rapidly.

2. Avoid Sudden Temperature Changes

Extreme heat or cold can worsen cracks due to glass expansion and contraction. Parking under direct sunlight or turning on air conditioning at full blast on a hot day can cause stress fractures to spread.

• Park in shaded areas or use a reflective sunshade to reduce direct heat exposure.
• Gradually adjust heating/cooling inside the car instead of sudden temperature shifts.
• Avoid pouring hot water on an icy windscreen, as the sudden temperature change can cause immediate cracking.

3. Schedule Professional Windscreen Repair Before It’s Too Late

Once a crack starts spreading, at-home fixes won’t be enough. Mobile windscreen repair technicians can assess the damage on-site and use resin injection technology to prevent further spreading.

• Book a repair as soon as you notice a chip—delaying it could lead to a full windscreen replacement.
• Ensure professional-grade resin is used, as DIY repair kits rarely provide long-lasting results.
• Choose a mobile repair service for convenience and to avoid driving with a compromised windscreen.
  

Not every windscreen crack requires a replacement, but waiting too long can make repairs impossible. The decision depends on the size, location, and depth of the damage. A minor chip or small crack can often be repaired, but once it spreads or reaches a certain length, replacement is the only option. A windscreen repair is possible when the crack is smaller than a $2 coin (around 25mm in diameter) and doesn’t extend through both layers of glass. If the damage is located away from the driver’s direct line of sight, it can usually be fixed with professional resin injection, restoring both clarity and strength.

However, if left untreated, even a small crack can spread due to temperature changes, road vibrations, and external pressure, making a full windscreen replacement necessary. On the other hand, a replacement is unavoidable if the crack exceeds 15 cm in length, is located near the edge of the windscreen, or has already started to branch out into multiple fractures. Cracks in these areas weaken the glass’s structural integrity, making it unsafe to drive. Deep impact damage, where both layers of the windscreen have been compromised, also requires immediate replacement to maintain road safety.

The sooner you address windscreen damage, the more likely you are to avoid the cost and inconvenience of a full replacement. If the crack is still repairable, booking a Windscreen Repair service now can save you money and prevent further damage. For larger cracks that can’t be safely repaired, you can schedule meeting for free with our expert windscreen replacement team, that will ensure your vehicle remains roadworthy and safe.