Can I fix misted double glazing myself?

Not in any lasting way. Once moisture is inside the cavity the desiccant is saturated, and nothing applied from outside reaches it. Drilling holes and pumping in drying agents clears the mist for a while but removes the remaining insulation, and the mist returns. The only proper repair is a new sealed unit, made to the exact size and glass type of the old one.

How long does a replacement sealed unit take?

Manufacture usually takes a few working days after we have measured, because each unit is made to the exact thickness, spacer size and glass type of the original. Fitting on the day is typically under an hour per window: beads off, old unit out, drainage cleared, new packers, new unit in, beads back. The frame and the decorating are untouched.

When is a whole new window the right answer?

When the frame is cracked, badly discoloured, or an early design without internal drainage, or when you want to change the style or colour. Dropped hinges, stiff handles and perished seals are repairs, not reasons for a new window, and we can do them alongside a unit replacement in one visit. Our double glazing repair page covers that side.

Misted double glazing explained

Key takeaways

Mist between the panes means the sealed unit has failed, not the frame.
The fix is a new sealed unit in the existing frame, not a new window.
Drilling and drying treatments clear the mist briefly and remove the last of the insulation.
A misted unit is not dangerous; a cracked or insecure one is an emergency.
A typical unit is measured, made to size, and fitted in under an hour.

Misting between the panes of a double-glazed window is one of the most misunderstood problems we deal with. Customers often assume the whole window has to go. Salespeople are sometimes happy to let them think so. In almost every case, the frame is sound and the fix is a new sealed unit dropped into the existing frame, which is a fraction of the cost and disruption.

What a sealed unit is

A double-glazed unit is two panes of glass separated by a spacer bar, with the gap sealed and filled with dry air or argon. A desiccant inside the spacer absorbs any moisture that was present at manufacture. The whole thing is a sealed cavity. As long as it stays sealed, the gap stays dry and the glass stays clear.

The seal is a bead of adhesive around the perimeter. It has a working life, typically between ten and twenty-five years depending on the quality of the unit, how it was fitted and how much sun and rain the window gets. When it eventually fails, moist air gets in, the desiccant saturates, and water vapour condenses on the inside faces of the glass where you cannot wipe it.

Why units fail

South- and west-facing windows fail first, because daily heating and cooling flexes the seal thousands of times a year. Units that were fitted without proper packers, so the glass sits directly on the frame, fail earlier because water pools against the bottom edge. Blocked drainage holes in the frame have the same effect. In the Edwardian semis around Heaton Moor and Sale we see a lot of units from the first wave of uPVC replacements in the nineties, which are simply at the end of their life.

A unit that has misted is not dangerous and the window still works. What you lose is the insulation. A failed unit lets more heat out, and the condensation will gradually leave mineral streaks on the inside of the glass that do not clean off.

What does not work

Drilling holes and pumping in drying agents, sold as a repair, does clear the mist temporarily. It also removes what little insulation the unit had left, and the mist comes back. We do not offer it. Resealing the edge from outside does not work either, because the moisture is already inside.

What a repair involves

We measure the existing unit, including its thickness and the spacer size, and note the glass type. Obscure glass in bathrooms, toughened glass in doors and low-level windows, and any leaded or Georgian bar patterns all need matching. A new unit is manufactured to those dimensions, which usually takes a few working days.

On the day, we remove the glazing beads, lift the old unit out, check and clear the frame drainage, fit new packers, seat the new unit and refit the beads. A typical window takes under an hour. The frame is untouched, the decorating is untouched, and the new unit comes with modern low-emissivity glass that insulates better than the original ever did.

If the frame itself is damaged, the hinges have dropped or the window no longer locks, that is a separate repair, and we can do both in one visit. Our misted and failed units page covers the replacement in more detail, and double glazing repair covers hinges, handles and seals.

When it is worth replacing the window

Occasionally it is. If the frame is cracked, badly discoloured or a very early design without internal drainage, or if you want to change the style or colour, a new window makes sense. We will tell you when that is the case. More often, a customer asking about new windows has three misted units and perfectly good frames, and we can put that right for a fraction of the quote they were given.

A misted unit is planned work. We will give you a price per unit after measuring, with no obligation, and the pricing page explains how planned work is quoted. If a unit has actually cracked rather than misted, and the window is now insecure, that is an emergency and the emergency glazier page is where to go.

When to stop

Stop and call if the glass has cracked rather than misted, the window no longer locks, or the frame is loose.

Call 07343 065023