Blistered uPVC Bay Window Cill Repaired and Restored

The outer cill on this white uPVC bay window had blistered and split right along its length. A broad section of the surface had lifted and flaked away to reveal the substrate beneath, and the cracking was creeping further along the front edge above the brickwork. Sun and weather work on a cill like this until the coating fails, and once it splits, water tracks straight in and the lifting only spreads. Catching it early made this a straightforward repair upvc window job rather than a far bigger one.

Replacing a cill on a bay is disruptive and pricey, often dragging in the frame, the sealant and the surrounding render. A uPVC window repair kit from the shelf is no real fix here either, because feathering a flaked, split surface back to a smooth, even white and getting it to weather as one is genuinely skilled work. Our fully trained technicians took the engineered route, with proprietary materials and more than 30 years of experience since 1993. The lifted material was cut back to a sound edge, the void rebuilt and bonded, then the whole surface was filled, shaped and recoloured to match the existing finish in a single visit.

The after image shows a smooth, unbroken cill with a clean front edge and no sign of the blistering or the split, the repair flowing straight into the rest of the frame.

Got a blistered or split cill? See our uPVC window frame repair service, or get a fast online estimate and avoid a full cill replacement.