Windscreen Leaks

Leaking windscreens are a fairly common cause of leaks in cars, which can be fixed by refitting. While that sounds straightforward, there are a number of issues which deserve further explanation.

On modern cars, windscreens are not fitted into a frame, they are effectively glued to the outside of the car. A generous bead of sealant is applied to the outside of the frame and the windscreen is pressed against it.

There are four main reasons this fails:

1. When the windscreen was fitted, not enough primer and adhesive was applied, or the windscreen wasn't sufficiently pressed down into the adhesive. This problem is most common on replacement windscreens and may be caused by misalignment.
2. The adhesive failed to adhere to one of the surfaces due to improperly prepared surfaces. This is mostly likely to be on the glass, which has a matt black finish on the back, which serves both to hide the fittings and form a surface for the adhesive to key to. If this surface is contaminated with oils or grease, or there is a manufacturing defect in the coating, it is possible it won't properly bond.
3. Corrosion of the bodywork can occur under the windscreen. This will happen with age, but it can happen if there has been a replacement windscreen and the frame was damaged while cutting the adhesive from the old screen with a metal 'cheese wire'.  (How windscreens are removed).
4. The adhesive fails with age. Cars can get very hot in the sun and this will cook the adhesive over time, heat and cold also cause the car to expand and contract. Car bodies will also flex and twist as they go around corners. With the adhesive suffering from the climate and the movement in the frame, it is possible for the seal to leak in older cars.

If the leak is due to an incorrectly fitted windscreen, then you may well have recourse with the company who fitted the screen, especially if it was done through an insurance company. In our experience, they will usually pay for the refitting of the screen and additionally repair of water damage and drying. If the carpets are wet on the surface, then they will be wet underneath and so proper decontamination and drying could be required to rectify the problem properly -- a valet and shampoo will not be sufficient.

Therefore, we advise going to an independent company to assess the problem and cost of clean up.

What it means

Windscreen leaks are leaks where water comes past the front screen and into the car. Modern windscreens are usually bonded directly to the body with adhesive, while older cars may use a rubber seal that grips the glass and body flange. If the bonding has gaps, has not adhered properly, or the metal aperture has started to rust, water can track between the glass and the body and find its way into the cabin. The result is damp A-pillars, wet front footwells, water behind the dashboard or drips from trim and vents that sit below the screen.

Why it matters

• Can cause serious water damage: Water from a leaking screen often runs behind trim and carpets where it is not seen straight away, soaking underlay, wiring and soundproofing and leading to corrosion and mould.
• Affects safety systems: Many modern cars have airbags, sensors and wiring around the A-pillars and under the dash. Persistent wetting here can cause electrical faults and compromise safety systems.
• Structural and bonding issues: The bonded windscreen contributes to body stiffness. If corrosion around the aperture or failed bonding is bad enough to leak, it may also need proper body and glass work to put right.
• Often misdiagnosed: Because the water sometimes appears in the footwells or under the dash, windscreens can be blamed for leaks that actually come from sunroof drains, bulkhead grommets or heater intakes – and vice versa.

Where you’ll see it

You will see windscreen leaks mentioned in leak reports, glass company notes and water damage assessments. Typical comments include windscreen suspected leaking, evidence of previous screen replacement, corrosion at top of screen aperture, windscreen bonding failed in top corner or trace water path from screen down A-pillar into front footwell. On some cars technicians will note bad historic bonding or oversize screen fitted causing seal issues.

Context

Windscreen leaks are one of several ways water can enter around the front of the car. The scuttle panel, heater intake, bulkhead grommets, inner wings and door membranes can all let water reach the same general area if they fail. A proper diagnosis will normally include controlled water testing while trims are removed, so the technician can actually see whether water is coming from the screen edge or from elsewhere. If the windscreen is confirmed as the culprit, the usual fix is to remove the glass, deal with any corrosion on the aperture and then refit or replace the screen using correct methods and adhesives. Simply pumping sealant around the outside of the screen is rarely a reliable long term cure.

Common mistakes

• Blaming the windscreen for every front footwell leak without removing trims or water testing to see where the water is actually coming from.
• Trying to fix a leaking screen by smearing sealant around the outside edges, which often looks messy and usually fails once the car flexes or the sealant ages.
• Refitting a replacement windscreen onto a rusty or poorly prepared aperture, which prevents proper bonding and leads to repeat leaks and possible structural issues.
• Drying carpets and underlay in the footwells but ignoring the underlying cause at the windscreen, so damp, smells and electrical faults return later.

Written by Danny Argent. Last updated 08/12/2025 16:03