white and red wall with brown wooden window

What are the white marks between the panes of windows?

White marks between the panes of windows are a common issue that many homeowners face. These marks can be unsightly and may indicate underlying problems with the window seals or moisture buildup. Understanding the causes, types, and preventive measures for these white streaks can help in maintaining the appearance and functionality of your windows.

Key Takeaways

  • Seal failure is a primary cause of white marks between window panes, often leading to moisture buildup.
  • Moisture buildup between panes can result in white streaks, metallic sheen, or hard water spots.
  • Environmental factors such as sunlight exposure, temperature fluctuations, and humidity levels can exacerbate window discoloration.
  • Proper installation, regular maintenance, and the use of quality sealants are crucial in preventing white marks.
  • In cases of severe discoloration, options include cleaning techniques, seal replacement, or full window replacement.

Common Causes of White Marks Between Window Panes

photo of brown wooden window open

Seal Failure

One of the primary causes of white marks between window panes is seal failure. When the seals fail over time, moisture can penetrate, leading to condensation and cloudiness between the panes. This not only affects the appearance but also the insulation properties of the window.

Moisture Buildup

Moisture buildup is another common cause. When moisture enters the space between the panes, it can lead to the formation of white streaks and spots. This is often due to a breach in the seal or high humidity levels.

Desiccant Saturation

Desiccants are materials used to absorb moisture within the window panes. Over time, these desiccants can become saturated and lose their effectiveness, resulting in moisture accumulation and white marks. Regular maintenance and timely replacement of desiccants can help mitigate this issue.

Proper installation and regular maintenance are key to preventing these common issues and ensuring the longevity of your windows.

Identifying Different Types of Streaks and Spots

birds on body of water during daytime

White Streaks

White streaks are one of the most common forms of window discoloration. These streaks often run down from the top of the window and can be caused by various factors, including moisture buildup and soap residue. If the spots or visuals are between two panes, you have failure and ‘cleaning’ will not work.

Metallic Sheen

Metallic-looking spots or streaks can appear between the panes of double-pane windows. This is often due to issues with the low-E coating, which may develop over time or come defective from the factory. These metallic streaks are not just a cosmetic issue but can also indicate a deeper problem with the window’s insulation properties.

Hard Water Spots

Hard water spots often appear as white or cloudy patches on the glass surface. These spots are usually caused by mineral deposits left behind when hard water evaporates. While they are more common on the exterior surfaces of windows, they can also occur between panes if there is a seal failure.

One of the most obvious signs of window stains is visual discoloration or spotting on the glass surface.

Impact of Environmental Factors on Window Discoloration

white clouds on blue sky

Sunlight Exposure

Sunlight can have a significant impact on window discoloration. Blinds exposed to direct sunlight and harsh environmental conditions, such as high humidity, are more susceptible to fading, discoloration, and structural damage. Over time, UV rays can break down the materials in the window, leading to visible changes.

Temperature Fluctuations

Frequent changes in temperature can cause the materials in double-pane windows to expand and contract. This can weaken the seals and allow moisture to enter the gap between the panes. The resulting mold growing between your windowpanes then causes discoloration. It’s important to monitor and maintain a consistent indoor temperature to minimize this risk.

Humidity Levels

High humidity levels can lead to moisture buildup between window panes, which is a common cause of a discolored windowpane. When the vacuum-sealed gap between the panes traps moisture, it can result in mold and other forms of discoloration. Proper ventilation and the use of dehumidifiers can help control indoor humidity levels and prevent these issues.

Preventive Measures to Avoid White Marks

elevator door near firehose cabinet

Proper Installation

Ensuring that windows are installed correctly is the first step in preventing white marks. Proper installation minimizes the risk of seal failure, which can lead to moisture buildup between the panes. It’s crucial to hire experienced professionals who understand the intricacies of window installation.

Regular Maintenance

Regular maintenance is essential to keep windows in good condition. This includes cleaning the windows and checking for any signs of wear and tear. A damp microfibre cloth can often remove stubborn stains caused by external factors like old painted stonework or untreated lead flashing. Regular inspections can help identify potential issues before they become major problems.

Quality of Sealant

Using high-quality sealant during the installation process can significantly reduce the chances of seal failure. Quality sealant ensures that the window panes remain airtight, preventing moisture from entering and causing white marks. Investing in good sealant materials can save you from costly repairs in the future.

Regular maintenance and proper installation are key to avoiding the daunting task of eliminating stubborn stains caused by hard water on windows.

Repair and Replacement Options

white concrete building

Cleaning Techniques

When dealing with white marks between window panes, one of the first steps is to try various cleaning techniques. Specialized cleaning solutions can sometimes remove superficial stains. However, if the marks are due to internal condensation, external cleaning will not be effective.

Seal Replacement

If cleaning does not resolve the issue, the next step is to consider seal replacement. Over time, window seals can fail, leading to moisture buildup between panes. Glass replacement companies make replacement IGUs that can be installed in existing window frames. This process involves removing the old seal and installing a new one to restore the window’s integrity.

Window Replacement

In cases where seal replacement is not feasible or the window is severely damaged, full window replacement may be necessary. This option is more costly but ensures that the problem is completely resolved. When choosing new windows, it’s important to consider the quality of the sealant and the installation process to prevent future issues.

Ignoring a failed seal can lead to more significant problems over time, including increased energy costs and further damage to the window structure.

Understanding the Role of Desiccants in Double-Pane Windows

a white box with four white candles in it

Double-pane windows are designed to provide better insulation and energy efficiency by maintaining a consistent temperature between the glass panels. A crucial component in these windows is the desiccant, which helps keep the space between the panes dry and free from moisture.

Function of Desiccants

Desiccants are water-absorbing chemicals placed within the spacer tube between the glass panes. By absorbing atmospheric moisture and humidity, desiccants in double-pane windows keep them dry and protected against damage, corrosion, mildew, and bacteria. This ensures the longevity and effectiveness of the window’s insulation.

Types of Desiccants Used

There are several types of desiccants commonly used in double-pane windows, including:

  • Silica gel: Known for its high absorption capacity.
  • Molecular sieves: Effective at low humidity levels.
  • Activated alumina: Often used for its durability and efficiency.

Each type has its unique properties, making them suitable for different environmental conditions and window designs.

Signs of Desiccant Failure

When desiccants fail, you may notice condensation or fogging between the panes. This is a clear indication that the desiccant is no longer effective in maintaining a dry environment. Other signs include:

  • White streaks or spots on the glass.
  • A metallic sheen appearing on the window surface.
  • Increased difficulty in maintaining indoor temperature.

Regular maintenance and timely replacement of desiccants can prevent these issues and extend the life of your double-pane windows.

Desiccants play a crucial role in maintaining the clarity and efficiency of double-pane windows by absorbing moisture and preventing fogging. To learn more about how desiccants can enhance the performance of your windows, visit our website and explore our comprehensive window cleaning services.


In conclusion, the white marks between the panes of windows are often indicative of a failure in the window’s seal. This failure allows moisture to enter the space between the panes, leading to the formation of streaks and spots that are difficult, if not impossible, to clean. These marks can be caused by various factors, including the saturation of desiccant materials within the spacer bars or the buildup of hard water spots. While these issues can be unsightly and may affect the window’s insulating properties, they are generally a sign that the window unit may need to be replaced to restore its functionality and appearance.

Frequently Asked Questions

What causes white streaks on the outside of my bay windows?

White streaks on the outside of bay windows can be caused by various factors, including mineral deposits from rainwater, pollution, or residue from cleaning products. These streaks usually do not penetrate the glass and can often be cleaned off with the right products.

Why are there white streaks inside my double-glazed windows?

White streaks inside double-glazed windows are typically a sign of seal failure. When the seal fails, moisture gets trapped between the panes, leading to condensation and streaking that cannot be cleaned from the outside.

What is the metallic sheen or dots I see between my window panes?

A metallic sheen or dots between window panes often indicate a blown seal. This can look like a light coating of oil or rainbow-like colors and is usually more noticeable when looking from the outside in.

Can I clean the white marks between my window panes?

No, if the white marks are between the panes, cleaning will not be effective. This is usually due to seal failure, and the only permanent solutions are seal replacement or window replacement.

What are the white specs I see on my window?

White specs on windows can be due to soap residue, hard water spots, or desiccant material from within the window unit. If these specs are between the panes, it is likely due to seal failure.

Is it normal to see smear lines between double-glazed window panes?

No, it is not normal to see smear lines between double-glazed window panes. This often indicates that the seal has failed, allowing moisture and possibly desiccant material to create visible marks.