How to clean mould off window frames, sills and tracks after winter

To clean mould off window frames and tracks, vacuum loose dirt from the tracks, wash the frames, sills and seals with warm water and a little dishwashing liquid or a dedicated mould cleaner, scrub gently with a soft brush, then rinse and dry everything well. Spring is the right time to do it, once the worst of the winter condensation has passed.

Why window frames go mouldy over winter

On cold Christchurch mornings, warm, moist air inside the house meets cold glass and frames, and condensation forms. Water runs down onto the sills and pools in the tracks. Add a bit of dust and a few months of damp, and black spots soon appear on the frames, rubber seals and silicone around the glass.

Aluminium frames and single glazing tend to collect the most condensation, but double-glazed and timber windows can still get mould where water sits in corners and tracks.

What you’ll need

• Rubber gloves and good ventilation, with windows open while you work
• A vacuum with a crevice tool for the tracks
• Warm water with a little dishwashing liquid, or a mould cleaner suited to your frames
• A soft brush or old toothbrush, and a few microfibre cloths
• A dry towel to finish

Step by step

1. Open the window and vacuum dust, insects and grit out of the tracks and corners
2. Wipe the frames, sills and tracks with your warm soapy water to lift the surface grime
3. Apply your mould cleaner to the black spots and leave it for the time on the label
4. Scrub gently with a soft brush, paying attention to corners and the edges of seals
5. Rinse with clean water and a fresh cloth so no residue is left behind
6. Check the small drainage holes in the bottom track are clear, so water can escape
7. Dry everything thoroughly, then clean the glass last

Avoid scourers, steel wool and harsh abrasives. They can scratch powder-coated aluminium and damage rubber seals, which gives mould somewhere new to grip. If you’re unsure what your frames can handle, check your window manufacturer’s care guidance first.

When the mould won’t shift

Mould that has grown into silicone or rubber seals often leaves a stain even after it’s been cleaned. If the seal is cracked, perished or still black after a careful clean, it may need replacing rather than more scrubbing. A glazier or your window supplier can advise. Mould spreading onto walls, curtains or ceilings is a sign of a wider moisture problem worth looking into.

How to stop it coming back

• Wipe condensation off the glass and sills each morning in the colder months
• Open windows for a short time each day to let moist air out
• Use extractor fans when cooking and showering
• Dry washing outside or in a vented dryer where you can
• Keep heating steady, as a warmer house tends to have less condensation
• Keep tracks clear of dust so water drains away instead of sitting

Clean frames and tracks also help glass stay clear for longer, because grime isn’t pulled back onto it. Our window cleaning covers glass, frames, sills and tracks, and a spring house clean is a good time to reset the whole home. For more on technique, see why windows streak, and for growth on the outside of your home, read what’s the green and black stuff on my house.

Frequently asked questions