Window Seal Replacement in London: Gaskets, Draughts and Rattles

Every double glazed window relies on rubber seals to keep the weather out. There are gaskets that hold the glass in the frame, seals around the opening sash that close against the frame, and sealant around the outside where the frame meets the wall. When these wear, shrink or come loose, you get draughts, rattling sashes, whistling in the wind and sometimes water coming in. Mark replaces worn gaskets and seals on uPVC and aluminium windows, and reseals around frames where the outside sealant has failed.

Gaskets and wedge seals renewed
Opening sashes re-sealed against draughts
Single glazing reglazed and draught-proofed
Fixed price confirmed before any work starts
Often same-day where the diary allows

It helps to know which seal is which. Glazing gaskets, sometimes called wedge gaskets, sit between the glass and the bead on the inside, and between the glass and the frame on the outside. They hold the sealed unit firmly and keep water off the edge of the glass. The sash seal runs round the opening part of the window and squashes against the frame when it closes. Perimeter sealant is the bead of silicone or mastic between the frame and the brickwork outside.

Worn gaskets shrink back from the corners, go hard and cracked, or slip out of their groove. You can often see gaps at the corners of the glass. A worn sash seal shows as a flattened, split or missing rubber strip, and as a draught you can feel along the edge of the closed window. Failed perimeter sealant shows as cracking, gaps or dark staining around the outside of the frame, and can let water into the wall. Each is replaced on its own.

One thing resealing will not fix is misting between the panes. A sealed unit has its own internal seal round the edge, between the two sheets of glass. When that fails, moist air gets inside and the glass mists up. No amount of new gaskets or silicone can reverse that; the sealed unit itself has to be replaced. Our misted double glazed units page covers that repair. The gaskets are often renewed at the same time, because the glass is out anyway.

Draughts don't always come from seals. A window that has dropped on its hinges or needs its keeps adjusted won't press into its seals evenly, so new seals alone won't stop the draught. Mark checks the alignment as well as the rubber, so the repair actually works. Our guide to draughty windows and heat loss covers other causes.

Getting the right profile matters. Gaskets come in many shapes and sizes, and a seal from the wrong system either won't stay in its groove or won't compress properly. Mark matches the profile to your frame so the new seal sits snugly and lasts.

How the repair works

1. Find the draught Tell Mark where the draught, rattle or water is coming in, or send a photo of the seals.
2. Fixed price You get a fixed price confirmed before any work starts.
3. Renew and check Worn seals replaced, alignment checked, and the window tested shut against the weather.

Frequently asked questions

Can broken window seals be repaired?

Yes. Gaskets, sash seals and outside sealant are all replaceable. The exception is the internal seal of a sealed unit: when that fails, the unit itself is replaced.

Can a failed seal cause condensation?

A failed sealed unit causes condensation between the panes, which only a new unit cures. Worn gaskets cause draughts and leaks rather than misting, though cold draughts can add to condensation on the inside of the glass.

How do I know if it's the gasket or the unit?

If you see moisture or haze between the two panes that you can't wipe off, it's the unit. If you feel a draught, hear rattling or see gaps in the rubber, it's the gaskets or seals.