Updated
Paint, Plaster And Cement Splashes After Building Work
New or renovated windows covered in plaster dust, paint spots, silicone smears and cement splashes.
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What's happening?
A builders clean is a different job from window cleaning, and doing it as if it were ordinary washing is how new glass gets ruined. Fresh glass after building work carries several deposits at once: fine plaster and gypsum dust, emulsion and gloss spots, silicone smears from mastic work, mortar and cement splashes, adhesive from protective film and labels, and sometimes concrete slurry that has set. Each needs a different removal method, and several of them are abrasive — dragging cement dust across a pane with a cloth grinds it into the surface. Cement splashes are the serious one: mortar is alkaline and, left on glass wet, can etch the surface permanently, so the timing of the clean genuinely matters.
What usually causes it?
- Plaster, gypsum and cutting dust settling on the glass and then being wiped dry
- Emulsion and gloss overspray or brush spots from decorating without masking the glass
- Silicone and mastic smears left along the glazing bead after sealing
- Mortar, render and screed splashes thrown onto low glass during wet trades
- Adhesive residue and label glue left when protective film is pulled off late
- Concrete slurry or grout haze from floor and tiling work drying on the pane
- Scaffold rust marks and drips running down glass from tube and fittings above
Is it dangerous?
Not to you, but this is the highest-risk item on this list for the glass. Cement and mortar residue is alkaline and can etch a pane that no cleaning will recover. Metal blades used on dry or gritty glass leave permanent scratch arcs, and toughened glass in particular is prone to visible scratching from fine debris under a blade. If new windows are still under warranty, cleaning them wrongly is the fastest way to have a claim declined.
Can I fix it myself?
Careful rinsing, yes. Flood the glass with plenty of clean water first and keep it wet — the entire aim is to float dust and grit off rather than drag it. Then work on individual spots. Do not dry-dust the pane, do not use a blade on glass that is not fully wetted and free of grit, and do not use brick acid, cement remover or an abrasive pad on glass or on the frames. Cement splashes and setting slurry are the point at which to stop and get someone who does this: the window is easier to save now than later.
When should you call a window cleaner?
Call a window cleaner who offers a builders or sparkle clean, and call before the deposits cure. Fresh mortar and silicone come off; the same deposits after weeks of weather often do not, and etched glass has to be replaced. If the work is still ongoing, book the clean for after the last wet trade and the last decorating, so it is done once.
What will the window cleaner actually do?
- Flood and pre-rinse the glass so dust and grit float off before anything contacts the surface
- Remove paint and mortar spots with a correctly used blade on fully wetted glass, checking for coatings first
- Soften and remove silicone smears and label adhesive with a suitable non-abrasive product
- Clean the frames, rebates, glazing beads, sills and reveals where builders' debris sits
- Clear the frame drainage slots and trickle vents of plaster dust and offcuts
- Rinse with deionised water and identify any pane already scratched or etched, in writing, before handover
Frequently asked questions
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