How to Re-Seal uPVC Windows: Step-by-Step Guide

Feeling a draught coming through your windows? Seeing cracked sealant or small gaps between the frame and wall? It might be time to re-seal your uPVC windows.

In the North East, homes take a beating from rain, wind, and cold weather — and over time, the original window sealant can fail. At Windows and Doors Newcastle, we regularly help homeowners improve comfort and energy efficiency with a simple re-seal.

If you’re looking to do it yourself, here’s a straightforward, step-by-step guide to re-sealing uPVC windows properly.

What causes window sealant to fail?

It’s normal for sealant around uPVC frames to wear down over time. Common causes include:

• Constant exposure to damp and cold
• Building movement causing small shifts
• Ageing sealant that’s dried out or cracked
• Poor installation or shortcuts on older properties

If left untreated, failed seals can lead to draughts, water ingress, and even internal damp or mould.

Signs your windows need re-sealing

• You can feel cold air coming in around the frame
• You see visible cracks or gaps in the sealant
• There’s mould or damp around the window edge
• Water is leaking in during heavy rain
• The room feels colder than others, even with heating on

If any of these sound familiar, it’s worth resealing the affected windows.

Tools and materials you’ll need

• External-grade silicone sealant (clear or white)
• A caulking gun
• A sharp utility knife or sealant remover tool
• Soapy water in a spray bottle or bowl
• A rag or microfibre cloth
• Masking tape (optional, for a neat finish)
• A sealant smoothing tool or your finger

Choose a high-quality, weatherproof silicone rated for external use. Avoid generic filler or decorators’ caulk — it won’t last outdoors.

How to re-seal a uPVC window

1. Remove the old sealant

Use a sharp knife or specialist sealant remover tool to cut and pull away the old sealant. Work slowly to avoid damaging the frame or surrounding wall. Remove as much of the old seal as possible.

2. Clean the area

Wipe down the gap between the uPVC frame and wall with warm, soapy water. Remove dust, dirt, mould, or debris. Let it dry completely before moving on.

3. Prepare your caulking gun

Cut the nozzle of your sealant tube at a 45-degree angle and load it into the caulking gun. If you want clean lines, run masking tape along either side of the area to be sealed.

4. Apply the new sealant

Hold the caulking gun at an angle and apply a smooth, continuous bead along the joint between frame and wall. Try to avoid stopping and starting — work in small sections if needed.

5. Smooth the seal

Use your finger dipped in soapy water or a smoothing tool to press and smooth the sealant into the joint. Wipe away any excess. If you used masking tape, remove it while the sealant is still wet.

6. Let it cure

Leave the new sealant to dry fully. Most products will be surface dry within an hour but take 24 hours to cure completely. Avoid cleaning or touching the area until then.

How often should you re-seal?

In most North East homes, external window sealant will last 5–10 years depending on exposure. South-facing or coastal walls may need attention sooner.

If you’re seeing draughts, cracked sealant, or water staining — it’s time to check.

When to call a professional

Resealing is a straightforward DIY task — but some cases are better left to the pros:

• Windows on upper floors
• Irregular gaps or deep recesses
• Signs of deeper water damage or frame movement
• You’re unsure which sealant to use

At Windows and Doors Newcastle, we can inspect, reseal, and advise if a bigger repair is needed — no pressure, just honest advice.

Final thoughts

Re-sealing uPVC windows is one of the easiest and most affordable ways to boost warmth, stop draughts, and protect your home from the elements.

If you’re not sure where to start — or want the job done professionally — get in touch with Windows and Doors Newcastle. We’ll help keep your home sealed, secure, and comfortable year-round.