The Black Line Between the Panes: Why Warm-Edge Spacers Start Creeping

The Black Line Between the Panes: Why Warm-Edge Spacers Start Creeping

Every now and then we get shown a sealed unit where the customer has spotted something odd. The glass looks fine, but the black spacer running around the inside isn’t where they remember it being.

Usually it’s a corner that’s moved first. Instead of following the edge of the glass, it’s started creeping inwards.

It looks strange, but it doesn’t always mean the glass has failed.

So What’s Actually Moved?

The black strip you can see is the spacer. It runs between the two panes and keeps the gap between them consistent.

Older double glazing commonly had aluminium spacers. Most newer units use a warm-edge system, which helps reduce the amount of heat lost around the outside of the glass.

There’s more going on around that edge than you can see though. The spacer, seals and moisture-absorbing material all form part of the sealed unit.

That’s why a spacer moving can sometimes be purely cosmetic, while in other cases it can be an early clue that something isn’t right.

Why Would a Spacer Move?

Windows spend their whole lives heating up and cooling down.

A unit facing the sun can become surprisingly warm during the day before cooling right back down overnight. Do that over and over for years and the materials within the unit are constantly dealing with small amounts of movement.

Warm-edge spacers aren’t completely rigid either.

Because of that, seeing a slight bow in one section isn’t necessarily a disaster. We’ve seen plenty of glass where the spacer isn’t perfectly straight but there’s no misting, no moisture and no other obvious problem.

It’s the amount of movement that matters.

A corner that’s pulled well into the visible area of the glass, a badly twisted spacer or movement that appears to be getting worse is something we’d want to investigate.

Check the Glass, Not Just the Black Line

If you’ve noticed your double glazing spacer bar has moved, have a look at the glass itself.

This can tell you far more than the crooked spacer.

If both panes are clear and the movement hasn’t changed, you may simply be looking at an ugly spacer rather than a failed sealed unit.

Misting between the panes is different.

A quick check is to clean the glass on both sides. Still seeing the same cloudy patch or little beads of water? Then what you’re looking at is between the panes.

That’s the point where we’d be looking at the sealed unit itself rather than the spacer simply being out of shape.

Once water has found its way between the panes, there’s not much benefit in trying to do anything with the spacer. In most cases you’re looking at changing the sealed unit.

Have a Look Around the Window Too

Don’t only inspect the section of spacer that’s moved.

Follow it around all four sides and look closely at the corners. One slightly bowed section is very different from a spacer that’s twisting, separating or pulling a long way towards the middle.

While you’re there, have a quick look at how the glass is sitting in the frame as well.

Pay particular attention along the bottom. You don’t want to see damaged rubber seals or water hanging around underneath the unit. Windows are designed to let any water that gets into this area drain back out again, so it shouldn’t be sitting there.

If water is continually sitting where the edge of the sealed unit lives, that’s something you want sorting.

Can the Existing Spacer Be Put Back?

Not really.

Once that black spacer is behind the glass, you can’t reach in and straighten it. Removing the beads lets the complete glass unit come out of the window; the spacer itself is still shut away between the panes.

So if it’s only moved a little and everything is dry, clear and otherwise behaving itself, there’s usually nothing worth doing to it.

Start seeing mist inside the glass, or a spacer that’s continuing to wander, and that’s different. You’re then looking at whether the glass unit has reached the point where it’s better replaced.

The old unit needs to come out and be measured properly so the replacement matches what’s already there.

Packing matters as well. The new glass needs to sit properly in the sash or frame, with the right support underneath it. Get that wrong and you’re creating another problem before the window has even gone back together.

Need Replacement Glass in Bournemouth?

A wonky black line on its own isn’t enough for us to say a sealed unit needs changing.

We’d want to know what else is happening. Has it moved a tiny amount and then stayed there? Is the glass still completely clear? If so, you might decide you can live with it.

If it’s pulling further in, or you’ve started getting condensation trapped inside the glass, then it’s worth having the unit looked at.

For anyone fitting the glass themselves, you can bring the sizes and unit details down to DWC Trade Windows on Alma Road in Bournemouth. We’re at number 78.

We supply replacement glass in Bournemouth, sealed units and the other glazing bits you might need while you’re doing the job.

Give DWC Trade Windows a call on 01202 533126.

---