How to seal a window frame

Having "properly" sealed window frames plays a crucial role in maintaining your home's comfort and energy efficiency. An effective seal keeps drafts out and helps to regulate indoor temperatures. However, over time they can wear out, leading to increased energy bills and discomfort.

Understanding how to seal a window frame or reseal a window frame is essential for any DIYer. It can save money and enhance your living space. This guide will walk you through the basics of how to seal a window frame so you can master the task yourself. We'll cover the basics from what a window frame sealant is and why it's important, to diving into the detail with a step-by-step guide for sealing a window frame or resealing window frames.

Whether you're dealing with standard casement windows, bay windows or sash, we've got you covered. Let's dive into the world of sealing window frames...

A window frame sealant is a flexible silicone or hybrid polymer that’s applied around the edges of a window frame where it meets the wall or glazing unit. It is designed to adhere strongly to materials like uPVC, wood, aluminium, glass, brick, and plaster.

A window frame sealant's main role is to seal gaps and joints, creating a barrier against air, water, and sound infiltration. The flexibility within the sealant's formula ensures it remains elastic as the building shifts or expands with temperature changes.

Why window frame sealants are important?

If you have a broken seal on a window, you'll be familiar with the problems they can create in and around the home. A "proper" window seal is vital for many things, including:

• Weatherproofing – Prevents rainwater from penetrating around the window, reducing the risk of damp, mould, and structural damage.
• Energy efficiency – Stops draughts and heat loss, helping to lower energy bills and keep indoor temperatures stable.
• Noise reduction – Helps block outside noise for a more comfortable living or working environment.
• Structural protection – Limits moisture ingress that can cause frame rot (in timber) or corrosion (in aluminium/steel). If left untreated, water ingress can become a larger problem causing damp, peel paint, mould growth and damage plaster or insulation.
• Aesthetic finish – Provides a neat, professional-looking joint between the frame and wall.

First things first, you need to choose the best window frame sealant for your project. You're looking for a sealant that provides a flexible, long-lasting seal that can withstand movement and temperature changes.

EVO-STIK Window & Door Frame Sealant is a flexible, weatherproof sealant, perfect for sealing most window frames including aluminium, metal, and uPVC. It also provides excellent adhesion to mortar, brickwork, wood and other building materials.

Now you know what a window sealant is, why they're important, and the EVO-STIK sealant available, discover our step-by-step guide for sealing a window frame both inside and out.

Creating or replacing a window seal can seem daunting, but it’s manageable with the right approach. Start with gathering necessary tools:

What you will need:

• EVO-STIK Window & Door Frame Sealant
• Caulking gun / cartridge gun
• Sharp knife or sealant remover tool
• Wet, round-ended smoothing tool (do not use a wetted finger)
• Clean cloths
• Soapy water
• White spirit (for removing excess uncured sealant)

Optional:

• Masking tape (optional, for neat edges)
• Gloves
• Ladder (for exterior window frame seals)

If there is an existing cured sealant, carefully cut with a very sharp knife and gently peel it away from the frame.

Clean the area thoroughly with the cloth and soapy water to remove any leftover residue. The joint surfaces must be sound, clean and dry - free from dust, oil, grease and loose material.

Tip: If you're looking to achieve crisp lines, place masking tape along both edges of the joint before applying sealant - wait until the edges are clean and dry before doing this.

Unscrew the nozzle and cut the dome of the cartridge cleanly, taking care not to damage the thread. Then, screw the nozzle back on. Cut the tapered end of the nozzle at 45° to a width matching the gap to be sealed.

Insert the cartridge into the caulking gun: press the release plate and pull the plunger back, insert cartridge and squeeze the trigger until sealant appears.

Place the nozzle at the start of the gap and gently squeeze the trigger. Push the nozzle forward steadily so the bead contacts both sides of the joint. At the end of the run, release the trigger and depress the plunger release.

Smooth the bead with a wet, round-ended tool. Remove excess uncured sealant with a cloth moistened with white spirit, then remove masking tape while the sealant is still workable.

Wipe the nozzle and, before the sealant fully dries, complete the following checks:

• Check there are no gaps that can compromise the seal's efficiency.
• Verify that the window or door opens and closes seamlessly.

Allow a skin to form in 1–2 hours and up to one week for full cure - do not paint until fully dry.

That's it! You've now discovered how to seal a window frame indoors. Let's look at the necessary steps to creating a seal externally.

When you're sealing a window frame outdoors, the process is virtually the same as indoors - you can follow steps 1-5 as above. However, there are some additional considerations you must make to ensure a long-lasting, effective seal.

Check weather & timing

Pre-sealing

EVO-STIK Window & Door Frame Sealant will not be waterproof until fully cured and can be damaged by rain before it has fully dried. Complete exterior work only when you have a dry spell of weather long enough for initial skin formation (1–2 hours) and preferably longer for full cure.

Post application

If rain is possible before the sealant has cured, shield the joint (using a temporary cover or tarp). Wait until the sealant is fully dry before expecting it to be waterproof.
 

Regular maintenance can greatly extend the life of your window seals. Simple practices can make a significant difference. Performing checks and routine care helps keep seals in top shape for years.

• Clean regularly: Wipe seals with mild soap and water.
• Avoid harsh chemicals: They can degrade materials over time.
• Check for damage: Look for cracks or warping.
• Realign windows: Ensures proper seal contact.

Consistent attention prevents minor problems from becoming major repairs, protecting your home from drafts and leaks.

When to call a professional for a window seal repair

If persistent drafts or moisture persist after DIY efforts, professional help is wise. Complex issues, like misaligned double glazing seals, often need expert attention. Professionals can diagnose and fix problems efficiently, saving time and ensuring proper repairs.

Proper window seal application and maintenance enhances comfort, saves energy, and boosts aesthetics. With this guide, you’re equipped to tackle issues confidently. Make informed decisions when DIYing, and enjoy a practical, beautiful home.