Cracks Around Window Frame – How To Fix Them


Cracks in window frames can be an issue and one that can lead to significant problem if left unaddressed. Your window frame exists not only to hold your glass panes, it’s an important structural element of your home. Failure to repair the damage to frames can lead to a wide variety of problems that will affect your quality of life within your own home. 

But how can cracks in window frames be fixed? Here are some tips and advice for anyone considering dealing with cracked window frames themselves, though this guide is only for small to medium size cracks. More extensive damage may require a complete replacement.

We will explore the cause, the risks, and the steps to take to both repair and maintain your window frames in the future. Bear in mind that these type of repairs are often best handled by professionals, so if you are unsure, seek expert help.

Causes of Cracks

Before we address methods to repair your cracked double glazed windows, let’s take a look at the reasons that damaged them to begin with: 

  • Settlement – Buildings, over time, undergo a process named “settlement”. This is a natural phenomenon of architecture that involves the sinking of your house, essentially. The weight of the building crushes and compresses the soil beneath it. This compression can affect the walls and windows of your building in a couple of ways, including cracking your window frames. 
  • Weather – Extreme weather conditions can cause pressure on the window frames. Extreme doesn’t just mean heavy rain, thunderstorms and the like – but also the rapid temperature change, something that’s not entirely uncommon in the UK. This is more common in window frames made of wood. 
  • Construction issues – The poor construction of your windows may very well be to blame for your cracked window frames. Improper sealing and feeble structural support can lead to a lot of faults within a window, cracking being the most immediate. 


Risks of Leaving Cracks Untended

When a crack appears in a window frame, you should set about fixing it immediately for the following reasons: 

  • Energy loss – A crack in the window frame can lead to draughts, which not only means cold air will be infiltrating your home, but heat will escape. This means you’ll be paying more for energy whilst having less of it, leading to an expensive, less comfortable home. 
  • Water infiltration – Cracks can allow rainwater to seep into your home and cause water damage. This can lead to much more serious issues, as not only can water rot some materials (such as wood), but it can create damp areas which are perfect environments for mould to thrive. Mould is bad news, as prolonged exposure can cause respiratory issues.
  • Structural integrity loss – Cracks in the window frame create weak points in your home’s structure. Over time, this weak spot may get weaker, which can lead to all types of issues. 
  • Aesthetic damage – The most minor of the list, but still relevant, cracks just simply are not appealing to look at. Not only this, but it may lower the value of your home in the eyes of retailers and possible buyers alike. 


Materials Needed to Repair Windows

The following section will detail the tools required to carry out a small repair your windows. Each type of window (wood, aluminium and UPVC) will require different tools for the job.

Wooden Windows

  • Wood filler/putty – Required to fill in the cracks, providing a smooth and even surface. 
  • Sandpaper – Sandpaper is an abrasive material that is available in various levels of grit. It’s used to smooth and shape surfaces. 
  • Primer – Primer is applied to your window frame before applying paint to aid the adhesion. 
  • Paint – Paint is required to paint over the filler to ensure that the appearance remains uniform. 
  • Putty knife – This wide and flat blade will be felt in applying a smooth helping of wood filler/putty. 


Aluminium Windows

  • Hacksaw/metal cutting blade – This saw is for cutting into metal, and is used to get rid of the damaged sections.
  • Metal File – The metal file has a rough surface used to shape and smooth out metal. 
  • Aluminium Putty – This is a specialised filler for aluminium. 
  • Cleaning Solution – Cleaning solutions can help remove tough stains. 


UPVC Windows

  • UPVC cleaner – A cleaning solution that is used specifically for UPVC surfaces to prepare for maintenance/repairs.  
  • UPVC lubricant – This lubricating spray is required to ensure hinges, handles and other moving parts of the window operate smoothly. 


Repairing Wooden Window Frames

The following is a condensed guide to repairing wooden window frames: 

  • Removing existing paint – Use sandpaper to scrape away the existing paint. 
  • Repair cracks – Fill in the cracks with wood filler, and smooth it out with a putty knife. After drying, sand it for a clean finish. 
  • Sand and prime – Sand the repaired area for a smooth finish and apply primer to seal the wood. 
  • Finish with paint – Apply several layers of fresh paint. Ensure you allow time to dry between layers.


Addressing Rotten Wood

Rotting wood in your window frame is a bad sign. The only way to repair rotting wood is to replace it, which is a lot of work, not to mention a heavy DIY job. We would recommend anyone dealing with rotten window frames to contract a professional.

Repairing Aluminium Window Frame

  • Clean – Clean the cracked area with a cloth. You may need a cleaning solution for harder-to-remove dirt/debris. 
  • Prepare the crack – You may need to widen the crack to ensure that your filler penetrates deep within.
  • Apply metal filler/epoxy – Choose a high quality metal filler suitable for aluminium and fill the crack. Use a putty knife to smooth it all into the crack. Stop when it begins to overflow and cannot handle anymore. 
  • Smooth the surface – Once the filler has been applied, smooth out the surface of the window frame to make it flush with the frame’s surface. Then allow it to dry, use the product’s instructions for reference. 
  • Sand the repaired area – Sanding the area will allow the surface to be even and smooth, ensuring that the area you will paint will mask the filler and not leave anything protruding. 
  • Paint the frame – Finish with a paint job to hide the filler. Let it dry afterwards, and you’re done. 


Addressing structural damage

Structural damage in the aluminium, including heavy cases of severe rusting/rotting, will require a professional to address, as it may result in the need to replace the frame entirely.

Repairing UPVC Window Frames

  • Clean – Start a thorough cleaning task of the crack and the surrounding area. It’s best to use fragrance-free products, as well as a cleaning solution suitable for UPVC.
  • Apply compound – The specialised UPVC repair compound should come in two parts, requiring mixing before application. Apply it using a putty knife and ensure it seeps deep into the crack. Above it should be a good, smoothed layer. 
  • Sanding and final touches – Once the compound fully dries, sand it down with a coarse grit like 20, and move on to a more fine grit (600). Blend the repair into the UPVC, then wipe the area again with a cleaning solution. 
  • Paint (if necessary) – If you feel it necessary, this is the point in which you can paint. 


Addressing Larger Cracks

UPVC is a tougher, more resistant material. Cracks in UPVC are fairly rare and likely indicative of a larger problem. We do not believe UPVC to be a material that major DIY work can be carried out on so if you have issues, consult with Ultraseal.


All in all, cracked window frames needs to be addressed to prevent more major issues. While you can in some instances attempt minor repairs to a window frame, we would usually recommend you seek expert help.

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