Service gaskets for windows - EPDM rubber
Gaskets for servicing and resealing older windows. EPDM rubber - resistant to UV, ozone and frost, still springy where the old gasket has long given up.
After a dozen or so years the gasket in a window hardens, shrinks and stops closing the gap. The window starts to draw, the glass mists up and heating bills rise in winter. Replacing just the gasket costs a fraction of a new window and in most cases is entirely enough to restore the seal.
We supply service gaskets for PVC, aluminium and timber joinery - for windows and doors. We match them to the specific profile, from a piece of the old gasket or a photo of the groove cross-section.
Rebate gasket (with sealing lip)
The main service gasket - it runs around the sash and closes the window
It is held in the profile by an anchor foot, commonly called a fir-tree foot. The foot is pressed into the groove, so the gasket needs neither adhesive along its whole length nor the sash to be removed.
What we look at when choosing
| Feature | What it determines |
|---|---|
| Foot width | Must match the groove in the profile - it decides whether the gasket stays put |
| Lip height (G) | Sets the pressure and whether the window closes without resistance |
| Hardness | About 60-70 Sh A - soft enough to seal, springy enough to recover its shape |
| Colour | Black, grey, beige, brown, golden oak |
Glazing gasket (with hollow bulb)
It works between the glass and the glazing bead
The bulb has to match the clearance between glass and profile. Too soft and it will not hold pressure; too hard and the glazing bead will not click into place.
Mullion gasket (hollow-chamber)
Hollow-chamber profile with a sealing wedge - for mullions and structural couplers
Locating wings on either side of the base stop the gasket twisting in the groove as it is pressed in.
Material
Why EPDM rubber rather than ordinary rubber
EPDM stands for ethylene propylene diene monomer. It is a synthetic rubber that has replaced older rubber compounds and soft PVC in window gaskets.
The difference only shows after years. EPDM does not crumble under UV or ozone, does not harden in frost and does not stretch permanently under the pressure of the sash. It works roughly between -40 °C and +90 °C, so neither winter frost nor a sun-heated frame changes its properties. Typical hardness for window gaskets is around 60-70 Sh A.
An old gasket that does not spring back under finger pressure, is flattened along its whole length or cracks when bent is due for replacement. That is the most common cause of a leaky window - more common than worn hardware.
What you can replace yourself
The rebate gasket - without removing the sash or the glass
Pull the old gasket out of the groove by hand, starting at a corner. Wipe the groove dry to clear dust and remnants of old rubber. Press the new gasket in by its foot, again from the top corner, and work your way round. Never stretch the gasket - lay it in loosely, because a stretched gasket will shrink over time and expose the corners. Cut it with a small allowance only once the whole perimeter is laid, and join the ends butt to butt with a drop of rubber adhesive.
What is better left alone: the glazing gasket, because it means taking off the glazing bead and it is easy to loosen the glazing in the process, and gaskets in aluminium windows and hollow-chamber constructions. For that sort of work it is worth calling a fitter.
We describe it step by step in our guides.
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