Never wipe builders' dust off glass dry. Soak it with plenty of water first so the grit floats off, rinse, and only then wash and squeegee. Soften mortar and plaster before lifting them, and keep scraper blades away from toughened glass.
Why new windows get scratched
Plaster, brick and concrete dust is full of hard, sharp particles. A dry cloth, a squeegee or even a sponge drags them across the glass, leaving fine scratches you'll see every time the sun is low. Most of these happen in the very first clean.
Step by step
- Hoover the frames and tracks first, so you're not washing grit back onto the glass.
- Flood the glass with clean water from a hose or bucket and let it run.
- Rinse again. You want the grit gone before anything touches the glass.
- Wash with a soft, wet applicator or sponge, rinsing it often.
- Squeegee or dry with a clean microfibre once the glass is grit-free.
Mortar, plaster and render splashes
Soak them until they soften, then ease them off with a plastic scraper or your thumbnail. Don't use brick acid or patio cleaners on glass or uPVC; they can etch glass and mark frames.
Silicone smears and labels
Fresh silicone rolls off with a fingertip once it's fully cured. Labels come off after a soak; a little warm soapy water helps the glue. Avoid solvents on the rubber seals.
A word on blades
Many new windows, and all glass doors, use toughened safety glass. Glass makers warn that scraper blades can scratch toughened glass, because tiny particles on its surface catch under the blade. If you're not sure what glass you have, don't use a blade.
The protective film
Peel the film off frames as soon as the building work is done. After months of sun it bakes on and can be hard to remove cleanly.
If it's a whole house, an extension with large glass doors, or you'd rather not risk it, our after-builders window clean does the lot, inside and out.
What about mortar and cement spots?
Soften them with water and lift them one at a time. They bond to the glass as they cure, so patience works better than force. On toughened glass, avoid blades altogether. Our guide on getting cement and mortar off windows goes through it step by step.
And the protective film on the frames?
Take it off as soon as the work is done. In sunlight it goes brittle and bonds to the frame. If it's already baked on, warm it gently with a hairdryer and peel slowly with plastic tools. See removing protective film from uPVC windows.
Do the tracks and drainage slots need cleaning?
Yes. Sliding doors and windows collect sand, plaster and bits of packaging in their runners, and the drainage slots in the bottom of uPVC frames can get blocked. Vacuum the tracks, wipe them, and check water can escape through the slots.
When should you book a professional clean?
After the last dusty trade has finished and the scaffold is down. Our after-builders window clean covers glass, frames, sills and tracks with plenty of pure water and no dry wiping.