Short answer
After building work, wait until the dusty jobs are finished, then clean. Always wet the glass before removing dirt; dry dust and grit can scratch. VELUX’s care advice says never to clean dirt off a pane without first applying water, and not to use abrasive products. Plaster, paint and cement splashes may need separate care, so tell the cleaner about them first.
Why is post-build dirt different?
Normal window dirt is mostly fine dust, pollen and road film. Building dust is different: it can contain grit, sand and cement, which are hard and sharp. Rubbing them across dry glass is how scratches happen. Splashes of plaster, mortar or paint dry hard and stick to glass and frames.
What should I avoid?
- Dry wiping. Never rub dry dust across the glass. Wet it first.
- Abrasive pads and powders. They can scratch glass and dull frames.
- Scrapers on dirty glass. Scraping over grit drags it across the pane.
- Strong chemicals on glass, seals or frames.
VELUX’s guidance for its windows says the same things about applying water first and avoiding abrasive and chemical products, and suggests protecting the pane with a clean plastic sheet during nearby building work.
When should I book the clean?
After the dusty work is done: plastering, sanding, cutting, rendering and brick cleaning. If you clean too early, the glass gets dusty again. For extensions, that often means after the outside work is finished and the scaffolding is down.
Can pure water clean building dust?
Pure water and a soft brush rinse off loose dust well, because there’s plenty of water carrying the grit away rather than rubbing it in. Hard splashes of mortar, plaster or paint are a different job. I’ll tell you what I can and can’t remove, rather than risk scratching the glass.
What about new windows?
New windows sometimes arrive with protective film, stickers or sealant marks. Take off the film as the fitter recommends. Sticker residue and sealant smears need care; tell me about them before I clean.
What about frames and sills?
Building dust settles on frames and sills and then runs onto the glass when it rains. That’s why it’s worth asking about frames and sills as well as glass. On new uPVC, dust usually comes off easily. On timber with fresh paint, wait until the paint has fully hardened. Cleaning uPVC frames and sills has more.
What about conservatories and roof lanterns?
New roof glass, especially lanterns on flat-roof extensions, collects building dust from above. Whether I can reach it safely depends on height and access. Conservatory and bay window cleaning explains what I need to know.
Is a one-off clean best?
Usually, yes. A one-off clean after the work is done gets the glass back to clear. If you want to stay clear after that, a regular round keeps it there.
What if the builders are still on site?
If trades are still working, I’d wait. Clean glass next to a cement mixer or a disc cutter won’t stay clean for long. If there’s a gap in the work, like after the outside is finished but before the inside is decorated, the outside glass can be done then.
What about render and brick dust on the frames?
Render and brick dust is fine and pale, and it settles in every corner of a frame. It usually rinses off frames well with pure water and a brush. Where it has got wet and dried, it can leave a chalky film that needs more than one pass. Window seals and drainage slots can hold it too, so it may run out for a clean or two afterwards.
What about plaster dust inside?
Inside, plaster dust settles on sills, frames and glass. Vacuum sills and tracks before anyone wipes the glass, so grit isn’t dragged across it. Then the inside glass can be cleaned by hand with plenty of water. Inside window cleaning explains how I do it.
Common questions
Should the builder clean the windows?
Some builders include a clean at the end of a job, some don’t. Check what your contract says.
Can you remove paint from glass?
Small spots sometimes need a scraper on wet glass, which is a different job from a normal clean. Tell me and I’ll say whether I can help.
Will cement splashes damage glass?
Cement is alkaline and can etch glass if left for a long time. Getting it off sooner is better, with care.
Can you clean while scaffolding is up?
I’d rather wait until it’s down, so the glass doesn’t get dusty again and access is clear.
