Warm water, a drop of washing up liquid, a soft cloth. That’s the whole answer, and if you stop reading here you’ll have done your frames more good than most of what gets recommended online.
The rest of this page is about why everything else is a risk, because the products that promise to shift stubborn marks off uPVC are the same ones that leave the frame permanently duller than it was. We see the results often enough around Wishaw and Motherwell to be firm about it.
Two very different things get called uPVC
Before you clean anything, work out which sort of frame you’ve got, because it changes what you can safely put on it.
A standard white frame is coloured all the way through. The plastic itself is white. It has a smooth, slightly glossy skin from the extrusion process, and that skin is what sheds dirt and keeps it looking white, but the material underneath is the same colour. Scratch it and you don’t reveal a different colour, you reveal a rougher, more porous surface that grips dirt and discolours faster than the bit beside it.
A woodgrain, grey, black or cream frame is usually a different animal. Those finishes are a printed foil, a thin decorative film bonded to the white profile underneath. The colour is a surface layer measured in fractions of a millimetre. Go through it and you are looking at white plastic, and there is no polishing that back.
So on a white frame, aggressive cleaning dulls it. On a foiled frame, aggressive cleaning can take the finish off altogether. Same product, two quite different outcomes, and neither of them good.
What to actually use
Warm water and a squirt of washing up liquid in a bucket. A soft cloth or a sponge. A soft brush, an old washing up brush or a soft nail brush, for the corners and the moulded detail where a cloth won’t reach.
Wash it, rinse it with clean water, and dry it off with a cloth if you want it to look sharp rather than streaked.
For genuinely stubborn marks there are proper uPVC cleaners sold for the purpose, and used sparingly on a white frame they’re fine. Test on a hidden section first, the bottom of the frame behind an opener is ideal. On a foiled finish, be more cautious still and check the label says it’s suitable.
That is it. There is no secret product.
The list of things that wreck frames
Abrasive cream cleaners. The gritty ones sold for kitchen sinks. They work by scouring, which is precisely the problem. They will lift a mark and they will leave a matt patch where the mark was, and that patch will collect dirt from then on.
Melamine foam sponges, the “magic eraser” type. These get recommended constantly and they’re the worst of the lot, because they don’t feel abrasive. They are. The foam is micro abrasive and works like an extremely fine sandpaper. On uPVC it takes the gloss off in the shape of wherever you rubbed, and you can’t put it back. We’ve seen frames with a pale, flat halo around every handle where somebody has scrubbed the finger marks off.
Solvents. White spirit, acetone, nail varnish remover, brake cleaner, anything in that family. They soften the surface of the plastic, and on a foiled frame they can attack the adhesive holding the film down. Somebody gets paint on a frame, reaches for the white spirit, and swaps a small mark for a permanently cloudy patch.
Bleach. On white uPVC it does very little that soapy water wouldn’t. On a foiled finish it can bleach the colour out of the print, which is exactly as bad as it sounds. It also runs down into the seals, and bleach hardens rubber.
Pressure washers. This one costs people real money. A window is built to let a certain amount of rain past the outer seal and drain it back out through slots in the bottom of the frame. It is not built to have water fired at it under pressure. A jet wash drives water past the gaskets and floods the drainage chambers faster than they can empty, so it goes inward instead. On an older window the lance can lift a gasket clean out of its groove without you noticing until the first proper wind and rain. If you’re washing the house down, keep the lance off the windows.
The bits people forget
The drainage slots. Along the bottom of the outer frame on the outside, small slots, often with a little plastic cover over them. Those are the escape route for any rain that gets past the outer seal. Block them with moss and dirt and the water sits in the frame instead. Clear them with a cable tie or a thin stick, or flush them through with a plant sprayer. Nothing metal and nothing you could snap off in there.
The seals. Wash the rubber with the same soapy water and nothing else. If they’re looking dry and grey, a silicone rubber conditioner keeps them supple. Never a solvent, never oil, and never bleach. Rubber gaskets are cheap to replace and expensive to ignore, because a hardened seal lets in draughts and water long before it looks obviously perished.
The hinges. A light machine oil on the pivots, or a dry PTFE spray if you’d rather not have wet oil attracting dust. WD40 is a water dispersant and a penetrant, not a lubricant. It flushes out the grease that’s already in there, works for about a fortnight, and then you have a dry hinge. Fine for freeing something seized, wrong as a maintenance product.
If the frame has gone chalky
Run a dry finger down an old white frame on a sunny elevation and if it comes away with a fine white powder on it, that isn’t dirt and you will not wash it off. That’s oxidation, the surface layer breaking down under years of ultraviolet light, and no amount of scrubbing will touch it. Scrubbing harder just accelerates it.
That’s a different job with a different answer, and we’ve covered it separately in the article on yellowed and chalky uPVC frames.
Before you scrub
If you’ve got a mark you can’t shift and you’re weighing up something stronger, send us a photo on WhatsApp first. It takes a minute to say whether it’ll come off or whether you’re about to make it worse, and we’d rather tell you for nothing than be called out afterwards. The number is 01698 604 278, Monday to Friday.
Cleaning is the easy half. The hinges, the locks and the drainage want doing too, and that is what a window service covers.
Related advice
If you would rather just ask, get in touch.
Stuck on something else? Our window and door advice section covers around fifty of the faults we see most.
Written by the team at Wishaw Window Repairs. Over thirty years repairing uPVC windows and doors across Lanarkshire.