Resealing Double Glazed Windows

window home installation

Double Glazed Windows are hailed as one of the best home improvement options, popular for their ability to retain heat within the home. They practically pay for themselves over time through the money that they enable households to save through reduced heating demand. 

Double glazing is effective as it consists of two window panes, with an insulating gas between them that stops heat passing through. But they are not infallible and problems can sometimes occur, especially over time.

One of the most common problems we hear regarding homeowners’ double glazing not working correctly is failed seals. When a seal is faulty, the double glazing loses its airtight ability and the argon gas is lost. This can in some cases be remedied, with resealing of your double-glazed windows a possibility. In this article, we will explore how to reseal windows, the possible causes of a failure, and maintenance tips to try ensure your seals don’t fail in future. 

How do I know if my window’s seal is faulty? 

Recognising faulty window seals is key to keeping your windows energy efficient and your house warm. The following may be signs that the seal of your windows is faulty and needs replacing: 

  • Draughts – This is a sure sign that your window is faulty. The entire point of double-glazing is to keep the heat in, but if cold draughts are finding their way into your home, then there must be gaps somewhere that need sealing. 
  • Distorted Reflections – A failing seal can result in distorted reflections in the glass. This is a result of the changes in pressure that are caused by a faulty seal. Part of what keeps the two window panes perfectly parallel is the pressure of the argon gas, and when that leaks, that parallel structure is lost, resulting in two panes giving reflections from different angles. 
  • Damaged Window Frame – This sounds like the most obvious sign of faulty window seals, but the term “damage” counts for a lot wider than you might think. Mould is an obvious one, but chipped paint and peeling are also signs that your window seals are damaged. Moisture is the cause, so try to keep your windows dry.


It’s important to check and ensure that your windows and doors are dry, do not produce draughts, and that the watertight seal or frame has no moisture.

Before we cover the repairing section, we should ensure that we have all the materials and tools required to facilitate the repair of your window seals.

Double Glazing Window Seal Replacement – Tools Required

To effectively reseal double glazing, the following tools are required.

  • Utility Knife – The utility knife will be used to cut through the old rubber seal surrounding the double-glazing window.
  • Putty Knife – This tool is useful for clearing out the old rubber seal and any debris from the window frame. The window frame must be clean.
  • Caulking Gun – A caulking gun is essential. It’s used to apply the new window seals evenly.
  • Silicone Caulk – This is the material that will be used to reseal your windows. This is like a rubber seal and is very effective in blocking air from entering or leaving.
  • Caulk Remover and Gloves (May not need) – Caulk remover is a substance that dissolves the seal if the material is too hard to remove by itself.
  • Damp Cloth – A damp cloth is used to clean the window after removing the window seals.
  • Scissors (or other sharp objects) – The tip of the caulk gun is blocked by a hardened caulk, exposed outside of its tube. To gain access to the un-hardened caulk, you have to snip the tip off.
  • Gasket Seal – There is a huge array of gasket seals available, such as wedge gaskets, bubble gaskets, rubber gaskets etc. Ensure you get the right Gasket for your window.
    • Wooden Windows – Foam, Rubber, Brush.
    • UPVC Windows – Bubble, Flipper, TPE.
    • Aluminium Windows – EDPM, Silicone, Wedge.


Wooden Windows

Wooden Windows and Doors require tools exclusive to them:

  • Coarse Sanding Paper
  • Grit Sanding Paper
  • Wood Filler
  • Primer


Step-by-Step Guide to Resealing Aluminium Double Glazing Windows

The following is the step-by-step guide to replacing aluminium double-glazing:

  • Removing old sealant and gaskets – Carefully slide your utility knife along the edge of the sealant. Ensure that you don’t damage the window frame, but try to cut as close to it as possible. This can be a bit scary, especially if the sealant is particularly hard. If so, use the caulk remover, but ensure that the room is well-ventilated and you wear gloves. Make sure you also remove the gasket seal gently if you have one.
  • Cleaning the area – The area where the new sealant is being applied must be cleaned. Use a damp cloth to remove the dust, dirt and debris – but then dry the area with the cloth.
  • Apply your new gasket seal – Measure the area where your gasket seal will be applied, and then cut. This will ensure a snug fit. Do a test fitting of your gasket, then install it into the window frame. Start from one corner and gently press it into the frame.
  • Applying new sealant – Cut the tip of the silicone caulk and proceed to load it into your caulking gun. Then, apply the caulk slowly and evenly across the window frame by gently squeezing the trigger. Make sure your movement is slow and smooth, and that the beads of caulk are even across the length of the frame.
  • Smoothing out – After applying the caulk, you must smooth it out. This is doable simply with a wet finger, dipped in water to prevent the silicone from sticking until satisfied. Then, use your wet cloth to wipe away any excess sealant.
  • Let it dry – Simply leave it alone. By leaving it be, it will eventually harden, and finally, you’ll have your windows resealed.


Step-by-Step Guide to Resealing Wooden Double Glazing Windows (And Doors)

Here’s a step-by-step guide to resealing your wooden double glazing, skipping the details of the steps that have already been covered.

  • Removing the old sealant and gaskets
  • Apply filler – If there are any gaps or damaged sections of wood, use a wood filler to fill those gaps.
  • Sand the wood – Sanding the wood now prepares it for the application of paint, stains and finishes.
  • Clean the area
  • Applying primer- Apply a primer to your wood, so you can protect it in future. It will also make the sealant that much more secure.
  • Apply your new gasket seal
  • Apply your sealant
  • Smooth your sealant
  • Allow the sealant to dry


This process, as you can see, is quite easy, and anyone with a little experience in DIY projects should be able to handle it.

Step-by-Step Guide to Resealing UPVC Double Glazing Windows (And Doors)

Reapplying UPVC Window Seals is much the same as aluminium, but UPVC is a trickier material due to thermal expansion.

  • Removing old sealant and gaskets – Be cautious about cutting too close to the UPVC frame, as whilst it’s more resistant, it’s weaker than aluminium and prone to damage.
  • Cleaning the area – Ensure the UPVC frames are dry, as they can be sensitive to moisture.
  • Apply new gasket seal – Measure, then cut the gasket a bit longer than your measurement. This is to account for the thermal expansion.
  • Apply new sealant
  • Smooth your sealant
  • Allow time to dry – Make sure it’s left completely alone, as it has to thermally expand.


When do I reseal, and when do I replace my double-glazed unit?

The issue with window seals failing is that argon gas will leak out of the unit. If you experience a noticeable decrease in temperature in your room after resealing and you’re sure the job was done correctly, then you may have to replace your window entirely. Once the argon gas has leaked, it’s impossible to get it back in. In these situations, you need a high-quality windows supplier like Ultra-Seal.


When window seals fail, it’s important to act on it immediately. Whilst the sealant is more or less easily replaced, the same cannot be said for the insulating properties of the windows.

Resealing Double Glazing – FAQs

At Ultra-Seal, we often receive frequently asked questions on the following.

What’s the difference between window gaskets?

Here is a quick list describing the different types of gaskets so you can make an informed decision about which replacement gasket is right for you.

  • Rubber gasket seal – A rubber gasket seal is flexible and durable, acting as a high-quality weather seal, ensuring that the window maximises its energy efficiency.
  • Bubble gasket seal – A bubble gasket seal is characterised by its curved shape indented with bubbles. Bubble gaskets are often used due to their ability to adapt and fill gaps in your double-glazed unit effectively.
  • E gaskets – E gaskets are made from materials like rubber but are designed with an E shape at the cross-section.
  • Flipper gasket – A flipper gasket seal is used for their ability to compress and seal gaps in the window, with heavy emphasis on airtightness.
  • Wedge gaskets – Wedge gaskets are designed to fit snugly, being crafted in a wedge shape.

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