How do I whiten uPVC that has gone yellow?

White uPVC yellows because ultraviolet light degrades the surface of the plastic and, on older frames, because the stabilisers used before the mid-1990s were less UV-stable. The distinction between surface and through-body yellowing decides everything.

What you'll need

• uPVC restorer or reviver cream
• A soft cloth and a soft brush
• Warm water and washing-up liquid
• A hidden test area

Step by step

1. Wash it properly first.A surprising amount of 'yellowing' is a film of traffic grime, pollen and algae. Warm soapy water and a soft brush, then dry, and reassess.
2. Test whether it is surface or through-body.Rub a small hidden area firmly with restorer cream. If white comes back, it is surface oxidation and treatable. If it stays yellow, the discoloration is through the material.
3. Use a proper uPVC restorer.These are mildly abrasive creams with a solvent component. They remove the degraded top few microns and expose sound plastic below. Work in small sections with a cloth.
4. Follow with a UV protectant.Restoring exposes fresh plastic to the same sunlight that degraded the old surface. A uPVC protectant or a silicone-based sealant slows the recurrence considerably.
5. Do not use bleach on the frame.Bleach does nothing to oxidised plastic, degrades the gaskets it runs onto, and can leave streaks. It works on mould, which is a different problem.
6. Avoid abrasive pads and scouring powders.They scratch the smooth outer skin. A scratched frame holds dirt in the scratches and goes grey permanently, which is worse than the yellowing.
7. Consider spraying for through-body yellowing.Specialist uPVC spray coatings, applied properly with the right primer, look excellent and last many years. It is a trade job and needs masking and dry weather.
8. Consider a foil wrap as the alternative.An adhesive architectural film applied to the frame. Good for a colour change as well, and reversible, but the preparation has to be thorough.
9. Do not use ordinary paint.uPVC rejects household paint. A specialist uPVC primer and paint system exists and works, but ordinary gloss peels off in sheets within a season.
10. Deal with the gaskets separately.Black gaskets going grey and chalky respond to silicone grease. That alone smartens a window noticeably.

Tips

• South and west elevations yellow first and worst. If one side of the house looks fine, that is a strong clue it is UV rather than dirt.
• Restorer cream on a cloth, not a pad, and light pressure. You are removing microns, not scrubbing.
• A frame restored and then protected annually stays white far longer than one restored and left. The protectant is the part people skip.

Common mistakes

• Attacking it with a scouring pad or wire wool — The gloss skin on uPVC is what keeps dirt on the surface where it can be washed off. Once it is scratched, dirt embeds in the scratches, the frame greys, and no cleaning will recover it.
• Painting uPVC with ordinary exterior gloss — Household paints cannot key to the low-energy plastic surface, and the frame's thermal movement is far greater than the paint film can accommodate. It flakes within months.

If it doesn't work

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