The builders have gone, the dust has settled, and your windows are speckled with paint, plaster and grey cement splashes. Most of it will come off without damage if you match the method to the mess. Here is how to do it safely, and what to watch for in Bristol's mix of period and modern homes.
The three usual culprits behave differently, so one method will not shift them all. Emulsion and other water-based paints sit on the surface and release once softened. Plaster and filler splashes are soft but full of fine grit. Cement, mortar and render are the ones to worry about: they are alkaline and can etch glass permanently if left for more than a few weeks, especially on south-facing panes that bake in the sun.
Run a fingernail over a speck. If it flakes off, it is paint. If it crumbles to powder, it is plaster. If it feels like sandpaper and will not budge, treat it as cement.
Most scratched windows we see were damaged by someone scraping dry glass or dragging grit under a blade. Keep everything wet and let soaking do the hard work.
Bristol's housing stock makes this trickier than it sounds. Georgian and Victorian sashes in Clifton, Redland, Cotham and Montpelier often still have original hand-made glass, which is thinner, softer and easy to scratch or crack. Much of it sits in conservation areas or listed buildings, where like-for-like replacement is slow and expensive, so avoid blades and stick to soaking and plastic scrapers.
Newer extensions and loft conversions in places like Bishopston, Southville and Horfield bring a different risk. Toughened glass in bifold doors and roof lights can carry tiny manufacturing particles on the surface that a metal blade will catch and drag, leaving fine scratches. Self-cleaning roof glass has a coating that blades and abrasive creams will strip. Check the etched stamp in the corner of the pane and the installer's paperwork before you start.
On frames, keep acetone, cellulose thinners and wire wool away from uPVC and powder-coated aluminium. A uPVC cream cleaner or warm soapy water is enough for most splashes. Acid-based cement removers will mark aluminium and natural stone sills, including Bath stone, so mask them off.
A few paint flecks on standard double glazing is a fair DIY job. Allow 15 to 30 minutes per window if you do it properly. It is worth getting help when there is cured cement or render across several panes, when the glass is toughened, coated or original period glass, or when the windows are above ground floor and need safe access.
Prices around Bristol depend on the number of panes, how heavy the contamination is, access and parking. As a rough guide, a builders' clean of the windows on a typical three-bedroom terrace tends to fall somewhere between £120 and £300, with large glazed extensions or heavy cement staining costing more. Compare that with replacing a single scratched double-glazed unit, which commonly runs from £100 to £300 or more. Ask for a quote based on photos or a visit, not a flat rate.
If your builder caused the mess, raise it before paying the final invoice. Removing splashes is usually part of leaving the job tidy.
On standard float glass, a new blade used on wet glass at a shallow angle is generally safe. On toughened, coated or old hand-made glass it can scratch, so use a plastic scraper and soaking instead.
Deal with them as soon as you can, ideally within a couple of weeks. Cement is alkaline and can etch the surface over time, and once the glass is etched no cleaning will bring back the clarity.
It is best avoided. Brick acid can damage aluminium frames, seals, stone sills and coated glass, so use white vinegar or a cement remover made for glass and rinse thoroughly.
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