Why Is the Sealant Around My Window Frame Cracking or Pulling Away?
For cracked, split or detached sealant around the perimeter of a window frame where it meets brickwork, render, plaster or another surrounding finish.
What this usually means
Perimeter sealant has to stay bonded while the window frame and surrounding building materials move slightly with temperature and weather. Geocel describes external frame silicone as a flexible weatherproof seal designed for window and door frames, while Sika's frame-seal products are intended to remain flexible and maintain adhesion. If an old bead has cracked or pulled away, the joint can admit draughts or rain and should be removed and resealed properly rather than simply smeared over.
What may be causing this
The old sealant has aged and lost flexibility
Clues: The bead is hard, brittle or split along long sections of the frame.
What to do: Remove the failed bead and replace it with a suitable flexible frame sealant.
The sealant has lost adhesion to one side of the joint
Clues: The bead is intact but has peeled cleanly away from the frame or masonry.
What to do: Clean and prepare the joint properly before resealing so the new material bonds to both surfaces.
The joint moves more than the sealant can accommodate
Clues: The same section repeatedly cracks where frame and wall movement is greatest.
What to do: Use a sealant with suitable movement capability and have excessive frame movement investigated.
Water, dirt or poor preparation prevented proper bonding
Clues: The sealant failed soon after installation and the surface beneath is dusty, damp or contaminated.
What to do: Remove the failed material, prepare the surfaces correctly and apply a compatible product in suitable conditions.
How to check what is happening
Ageing or insufficient flexibility is likely.
Adhesion failure is the main issue.
The failed perimeter joint may already be affecting weather-tightness.
The sealant may be failing because the frame or fixing needs attention, not only because the bead is old.
Can you fix this yourself?
Do not apply a fresh bead over cracked old silicone and expect a lasting fix. Remove the failed material, clean the joint and use a frame sealant suitable for the frame and surrounding surface. If the window itself moves or rain still enters after resealing, a window fitter should check the installation.
- Sealant remover or scraper
- Cleaning cloths
- Masking tape
- Compatible external frame sealant
- Sealant gun
- Gloves
What you can safely try
- 1
Work out whether the bead is cracked or has lost adhesion
A brittle split and a clean peel-away failure can point to different underlying causes.
- 2
Remove failed sealant rather than covering it
Fresh sealant needs sound, clean surfaces to bond properly.
- 3
Prepare the frame and wall surfaces
Remove dust, loose material and contamination and follow the sealant manufacturer's preparation instructions.
- 4
Apply a suitable flexible frame sealant
Use a product designed for the frame material, exterior exposure and expected joint movement.
- 5
Check for draught or rain after curing
If the joint still leaks, the problem may involve flashing, frame fixing or another part of the window installation.
Call a window fitter if…
- The window frame itself is loose or visibly moving.
- Water is entering despite an intact perimeter seal.
- The surrounding timber, plaster or masonry is badly damaged.
- Safe access would require leaning out or working at height.
- The same joint fails repeatedly after correct resealing.
Get the right window fitter.
We already know this problem maps primarily to a window fitter. Choose the closest type of work, add your postcode and continue in the form.
Sources used for this guide
We prefer primary UK guidance, regulators and manufacturers for technical and safety-sensitive claims.
Last reviewed: 2 September 2026. Home Manual updates review dates only when the substance of a guide is checked or changed.