Every Window Has a Weak Spot: A Cleaner’s Field Guide to Sash, Casement and Bi-Fold Frames

People often ask me which window cleaner I recommend. The honest answer is: it depends on the window. A squeegee that glides across a modern casement can be a liability on a Georgian sash. A microfibre cloth that’s perfect for a bi-fold track will leave streaks on a Crittall pane if you use it wet. The glass is usually the easy part. The frame, the seals and the hardware are where the real work lives.

Here’s a run through the window styles I see most often around here, the traps each one sets, and the checks worth making before you start.

Georgian and Victorian sash windows

Sash windows are the classic British window, and they’re lovely. They’re also a bit of a diva. The sliding sashes run on cords and weights hidden in the frame, and the meeting rail in the middle is a magnet for dust, spider webs and general grime.

The main trap is water. If you flood a sash window, water can get into the frame, sit in the sill, and find its way into the cords or the paintwork. Over time, that means rot or a sash that no longer runs smoothly. Use a controlled amount of water, work top to bottom, and keep a dry cloth handy for the sill and the meeting rail.

Check the putty or beading around the glass. If it’s cracked or missing, water can get behind the pane. Check the cords too — if they’re frayed, the sash is on borrowed time. And if the window is painted shut, don’t force it. That’s a job for a carpenter, not a cleaner.

Casement windows

Casements are the workhorses of UK homes: side-hung, top-hung, sometimes both. They’re usually easy to clean because they open outwards, but that’s also the trap. Leaning out of an upstairs window to reach the outside pane is not worth the risk. If you can’t reach it safely, use a proper pole or leave it to a professional.

The hinges are the weak point. Grit and dust collect there, and a stiff hinge can put stress on the frame. A quick brush and a little silicone spray (not a heavy oil that attracts dirt) will keep things moving. Check the rubber gaskets around the opening sash. If they’re perished, cracked or pulling away, you’ll get draughts and water ingress. Clean them gently and don’t pick at them.

Top-hung casements often have restrictors. Make sure they’re working. They’re there to stop the window swinging open too far, and they’re easy to overlook until a gust of wind reminds you.

Bi-fold doors

Bi-fold doors are brilliant for opening up a room to the garden, but they’re the most high-maintenance window style in the average home. The glass is straightforward; the tracks and hinges are not.

The bottom track is the main trap. It collects grit, leaves, pet hair and whatever else the wind brings in. If you don’t clear it, the panels start to drag and the hinges take the strain. Use a vacuum with a brush attachment first, then a damp cloth, then dry it properly. Don’t hose the track out. You’ll just push debris into the drainage channels.

Check the drainage holes at the bottom of the frame. If they’re blocked, water can pool and work its way inside. Check the seals between the panels too. They take a lot of wear, and a failing seal is a common cause of draughts and leaks.

And please, don’t use a pressure washer on bi-folds. It’s tempting, especially after a muddy winter, but it can force water past seals and into the frame. A gentle hand wash is always safer.

Crittall-style steel frames

Crittall-style windows — the slim steel frames with lots of small panes — are having a moment. They look great. They’re also less forgiving than uPVC.

The frames are usually painted, and the paint can chip. If you use an abrasive cleaner or a scraper, you’ll make it worse. Use a soft cloth and a mild solution, and dry the frame afterwards to reduce the risk of rust. Check the putty around the panes; old putty can crack and let water in.

The small panes mean more edges to detail. A squeegee is fine on the glass, but you’ll need a microfibre cloth for the frame and the corners. Work carefully, and don’t let water sit in the joints.

What to check on seals and hinges

Whatever the style, the checks are similar. Run a finger along the rubber seals. They should be soft and flexible, not brittle or gappy. Look for mould in the corners — it’s common in UK winters and it’s a sign that moisture is hanging around. Clean it gently and dry the area thoroughly.

For hinges, brush out grit, check for loose screws and lubricate sparingly with silicone spray. Don’t drown them. If a hinge is rusted or the window no longer closes squarely, get it looked at. It’s usually cheaper to fix a hinge than a frame.

Why technique beats product

It’s easy to think a stronger cleaner will solve a stubborn window. In practice, the opposite is often true. Harsh chemicals can damage seals, strip paint and leave a film that attracts more dirt. The right technique — a proper squeegee, a clean microfibre, a controlled amount of water, working top to bottom and detailing the edges — will beat the strongest product every time.

And if a window is high, awkward or already showing signs of damage, know when to stop. A professional clean is cheaper than a repair. That’s not a sales pitch; it’s just the maths.