You’ve probably noticed it on a cold morning. One pane looks foggy, there’s a film of moisture sitting inside the glass where you can’t wipe it away, and by the afternoon it’s cleared as if nothing happened. Then it’s back the next day. Wipe the inside, wipe the outside. It makes no difference, because the problem isn’t on either surface. It’s sealed in the middle.

If that sounds familiar, your unit has blown. It’s one of the most common calls we get across Wishaw and the wider Lanarkshire area, and the good news is it’s almost always a straightforward fix. You don’t need new windows. You very probably don’t need to spend a fortune. But there’s a fair bit of nonsense written about misted glazing online, so let’s clear it up properly.

Cross section of a double glazed sealed unit showing the two panes, the spacer bar, the desiccant beads inside it and the perimeter seal that fails and lets the misting in.
The seal round the edge is the part that fails. Everything else is doing fine.

What’s actually happened to the glass

A double glazed unit is two panes of glass with a gap between them. Round the edge sits a spacer bar, and inside that bar is a drying agent called desiccant, whose whole job is to soak up any moisture in the sealed gap and keep it bone dry. The unit is then sealed all the way round so no air, and no damp, can get in.

Over the years that seal starts to give up. Sometimes it’s age, plain and simple. Sealed units don’t last forever, and if yours are fifteen or twenty years old they’ve had a good run. Sometimes it’s a south-facing window that bakes in the sun and freezes overnight, expanding and contracting day after day until the seal fatigues. Once that edge seal fails, warm damp air creeps into the gap, the desiccant fills up and can’t cope any more, and you get condensation trapped between the panes. That misty film is moisture that has nowhere to go.

Here’s the part worth knowing: it’s only the sealed glass unit that’s failed. The frame, the hinges, the handles and the locks are all usually perfectly fine.

The myth that won’t die: drilling holes in the glass

Search this problem online and you’ll quickly stumble across people, and even a few companies, suggesting you drill a small hole in the pane, squirt in some drying solution, and reseal it. Some sell little kits for it. I’d steer well clear.

At best you’ll clear the fog for a few weeks before it drifts straight back, because the underlying seal is still broken and damp air is still getting in. At worst you weaken a pane of toughened glass that’s holding the weather out of your living room, and you’ve now got a hole in it. It also does nothing for the energy performance. A blown unit has usually lost the insulating gas that sits in that gap, so it’s colder than it should be, and drilling a hole certainly won’t bring that back.

The Glass and Glazing Federation and every reputable installer will tell you the same thing. There’s no spray, no trick, no gadget that genuinely restores a failed unit. It’s a nice idea. It just doesn’t work.

The real fix (and why it’s cheaper than you’d think)

Because it’s only the glass unit that’s gone, that’s the only bit that gets replaced. We measure the failed unit, make up a brand new sealed unit to match (same size, same spec, same style, whether that’s plain, obscured, Georgian bar or leaded) and swap it into your existing frame. The frame stays exactly where it is.

The whole job is usually done in well under an hour per window, there’s no mess, no ripping out, no plastering, and no redecorating afterwards. Our misted unit replacements start from £75, and honestly most people are surprised how modest it is compared with what they’d feared. Replacing the whole window when only the glass has failed is a bit like buying a new car because you’ve got a flat tyre.

Does the whole window need replacing? Almost never

This is the worry that stops a lot of people picking up the phone, so let me put it plainly. A misted unit is not a sign your windows are on their way out. It’s not a sign of rot, or damp in the wall, or anything structural. It’s a single component, the sealed glass, reaching the end of its life while everything around it carries on doing its job.

If you’ve got one blown unit, it’s worth keeping an eye on the others of a similar age, because units fitted at the same time tend to fail in the same rough window of years. But there’s no need to replace them all pre-emptively. Sort the ones that have gone, keep an eye on the rest.

Can you stop it happening again?

Not entirely, because seals will age eventually no matter what, but you can slow it down. Try not to blast the frames with a pressure washer, keep the drainage slots at the bottom of the frame clear so water isn’t sitting against the seal, and if you get heavy condensation on the inside of the room-facing glass in winter, a bit more ventilation helps the whole window last longer. A modern replacement unit fitted today should give you a good many years before you’re looking at the same thing again.

A few quick questions we get asked

Is misted glass dangerous? No. It’s a cosmetic and efficiency problem, not a safety one. The glass itself is still doing its job of keeping the weather out. It just looks awful and won’t insulate as well as it should.

Will it clear up on its own? It’ll come and go with the temperature, so some days it looks fine. But it won’t heal itself. Once a seal has failed it only goes one way.

Do you replace the whole window or just the glass? Just the glass unit, in the vast majority of cases. The frame stays put, which is exactly why it’s so much cheaper than a full replacement.

How do I know how much it’ll cost? Easiest thing is to send us a photo. Snap the affected window on your phone, message it over on WhatsApp, and we can usually give you a rough idea straight away before arranging to pop out and measure up properly.

Getting it sorted

We’re a family-run business and we’ve been fixing windows around Wishaw and Lanarkshire for over thirty years, so misted glazing is bread and butter to us. There’s no call-out charge and no hard sell, just an honest look at what’s gone and a fair price to put it right.

If your windows have started fogging up, send a quick photo over on WhatsApp or give us a call on 01698 604 278 and we’ll take it from there.

Misted units are the single most common job we get called out to. If you are over that way, we have a page on window repairs in Motherwell.

Misting is a glass problem rather than a frame problem, so the rest of the window stays as it is, although we will always flag anything else we spot as part of our usual uPVC window repair checks.

More on this

See our glass unit replacement page for what we do and where. There are before and after photographs of jobs like this in the gallery. If you would rather just ask, get in touch.

More like this: browse all fifty guides in our window and door advice section.

Written by the team at Wishaw Window Repairs. Over thirty years repairing uPVC windows and doors across Lanarkshire.