Plaster splashes on window frames are one of the most common things left behind after a London renovation, and one of the easiest to make worse. Scrape too hard or reach for the wrong cleaner and a five minute job becomes a scratched uPVC profile or a dulled aluminium finish. Here is how to do it properly, frame by frame.
Most new plastering in London homes uses gypsum finishes such as Multi-Finish, which set hard in about two hours and dry fully over a few days. In Victorian and Georgian terraces, especially in conservation areas like Islington, Hackney or Kensington, you may instead have lime plaster. Lime is strongly alkaline while wet and can mark timber and some paint finishes if left on.
Then check the frame material. uPVC, painted or stained timber, and powder coated aluminium all need slightly different handling. Look in the corner of the glass too: toughened safety glass carries an etched mark, and that matters later if you plan to use a blade.
If the plaster is still soft, wipe it off with a clean, damp sponge and a bucket of warm water, rinsing the sponge often so you are not just spreading grit across the frame. Do not wait for it to go off. Fresh plaster comes away in seconds; set plaster can take ten minutes per blob.
If you are having a room skimmed, ask the plasterer to mask the frames with low tack tape and polythene before they start. Most will do this as a matter of course, but it is worth confirming, particularly on new windows.
Once it has set, the trick is patience rather than force. Soak the splash with warm water and leave it for a few minutes so it softens. Then lift it with a plastic scraper or an old bank card, held at a shallow angle and pushed gently, never dug in.
For stubborn residue, a mix of roughly one part white vinegar to three or four parts warm water helps break down gypsum. Apply with a cloth, leave for five minutes, lift, then rinse thoroughly with clean water so no acid sits on the frame.
What to avoid on any frame:
Plaster dust and crumbs settle into the places you cannot see from across the room. On uPVC and aluminium windows, check the bottom track and the drainage slots on the outer frame. If these clog, rainwater cannot escape and can end up inside, which is a real problem in a wet London winter. A soft brush, a vacuum nozzle and a damp cotton bud will clear them.
On sash windows, check the staff beads, the pulley wheels and the parting beads, where gritty dust makes the sashes stiff. Also look at the rubber gaskets around the glass; wipe them gently rather than scraping, as they tear easily.
If your windows are new and still have the protective film on, remove it within a few weeks. Sunlight bakes the adhesive on, and it becomes much harder to get off later.
A razor blade scraper on wet, soapy glass, held flat at a low angle, will remove plaster from standard annealed glass. On toughened glass, which is common in doors, low windows and bathrooms, blades can cause scratches, so stick to soaking and a plastic scraper.
If a whole house has been replastered, doing every frame, track and sill by hand can easily take a full day. Many people book it as part of an after builders clean. As a rough guide, London prices for a full post renovation clean of a three bed terrace often fall somewhere between £300 and £700, depending on the amount of dust, access, and whether windows are cleaned inside and out. Getting a quote based on photos is usually the quickest way to know.
Diluted white vinegar is generally fine on uPVC for short contact times. Rinse it off with clean water afterwards and avoid using it neat or leaving it to sit for long periods.
Ideally do not wait at all and wipe it while wet. If it has already set, there is no benefit in leaving it longer, so soften it with warm water and lift it as soon as the plastering work in that room is finished.
On standard glass, a blade used flat on wet, soapy glass is usually fine. On toughened glass, identified by the etched mark in one corner, use a plastic scraper instead to avoid scratching.
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