Why won't the white marks on my glass come off?

01Why do the marks stay after the glass has been washed?

Most people call them water marks, water stains or just cloudy glass, and the first assumption is that the cleaner did not try hard enough. Usually the opposite is true. Once a pane has been washed properly and the haze is still there, the question stops being how hard to scrub and becomes what the marks actually are — because the stronger product that would shift a deposit is also the one that can damage the glass permanently.

Our guide to glass and high-access cleaning covers how this work is reached and priced. This is the narrower question underneath it: whether the marks on your glass will come off at all, and who should be touching them if they will.

If you already have photographs, send them to 014-313 0767 for a straight answer, including when the answer is that cleaning is not what the glass needs.

02Where do the white marks on building glass come from?

Most permanent-looking marks on building glass are left by water that ran over something else first, or by hard water that dried on the pane. Vitro Architectural Glass explains the first mechanism plainly: "When rainwater makes contact with a concrete surface, small amounts of silicate material dissolve into the water." Those solutions dry on the glass below and bond to it.

That is why the marks appear in streaks under a concrete ledge, a sunshade or a window head, and return in the same places after heavy rain. Vitro notes that with repeated run-down "the permanent deposits can build up and become quite unsightly", and that rainfall leaching alkaline material out of concrete "may cause surface staining and etching".

Hard water does it too. Vitro records that "Direct or windblown hard water spray from water sprinklers can produce tenaciously bonded inorganic residues on glass surfaces" — the spotted, cloudy film most people know from a shower screen, on a window instead. Anything else that keeps wetting the same pane and letting it dry, a hose or an overflowing gutter included, repeats the same cycle.

03How do you tell dirt from a bonded deposit from damaged glass?

A cleaner washes a small area properly and examines it in daylight. The National Glass Association recommends exactly that before any glass cleaning project: "it is strongly recommended that window cleaners test clean a small area of one window, then stop and examine the surface carefully for any damage to the glass and/or any exposed coating." Whatever is still there afterwards is not soil.

Light matters as much as the washing. The NGA paper states that "Daylight conditions are needed to properly evaluate a glass surface for damage", and notes that scratches invisible under a grey sky can be obvious when the sun is low.

One thing is worth observing before anyone comes out, and it is our own practical guidance rather than anything the two documents below say: run a fingertip across the mark. A deposit usually sits proud enough to feel, while etching tends to feel smooth, or like a shallow dip rather than something lying on top. It is a hint, not a diagnosis.

What neither settles is how far a bonded deposit has gone. Taking one off is specialist restoration work rather than cleaning, and the National Glass Association warns that any non-routine cleaning "carries a risk of irreparable damage to glass products" — so the honest next step is a tested patch, not a quotation written from a photograph.

04What can a cleaner actually do about each one?

Soil comes off with routine cleaning: the glass is soaked with clean water and a mild, non-abrasive solution, agitated to loosen the dirt, then squeegeed dry. A bonded deposit needs non-routine methods, which the National Glass Association lists as "the use of razor blades, chemical cleaning and/or mechanical polishing". Damage to the glass itself is not removed by any of them.

The cautions around that middle category are specific. The NGA paper says cleaning solutions "should not include acids, especially muriatic / hydrochloric" and hydrofluoric acid, and that razor blades and metal scrapers "should not be part of routine cleaning" at all. Where they are used, "Scraping should be done in one direction only with a new blade. Never scrape in a back and forth motion as this could trap particles under the blade that may cause scratches." On coated glass they are ruled out entirely.

On an Ipoh job those three are not equal, and it is worth being plain about which we do:

• Cleaning: yes. Our glass and high-access cleaning covers interior and exterior panes, shopfronts and facades, and the tracks, frames and seals that make clean glass look dirty when they are left.
• Blade work on cured renovation residue: yes. Paint spots, silicone smears and adhesive film are removed mechanically, with a blade at a shallow angle and plenty of lubrication.
• Chemical restoration or mechanical polishing of a bonded deposit: no. That is glass restoration, not cleaning, and nor do we remove scratches or etching, or repair, reseal or replace a pane.

05When is glass past cleaning?

Glass is past cleaning when the deposit has stopped sitting on the surface and started being part of it. Vitro Architectural Glass is direct about where long exposure to repeated spray leads: residue can build up that "cannot be removed by cleaning procedure in Attachment C", the restoration method its own document sets out, and then "Glass replacement may be the only practical remedy."

Being told that is worth more than paying twice to find it out. The same logic runs through whether a stained old floor can be restored without re-tiling: soil comes back with cleaning, damage does not, and the useful skill is saying which one a customer has before the invoice rather than after.

06How do you stop it happening again?

Wash it off before it dries, and do not let a renovation finish on dirty glass. The National Glass Association's instruction for building work is unambiguous: "During all stages of construction, the glass must be properly protected from construction debris such as cement, paint, varnish, adhesives and other construction material commonly found on job sites."

Protective film catches people out. Left on past its date in Malaysian sun, the adhesive cures onto the pane, and the NGA paper warns that failure to remove films by the manufacturer's recommended date "may result in aggressive methods being required to remove the film". For routine intervals its baseline is that "Generally, twice per year cleaning is sufficient; however, specific regions may require more frequent cleaning due to environmental factors and atmospheric pollutants." A sheltered elevation may sit at that; a shopfront on a busy Ipoh road will not. Where a renovation is the cause, our room-by-room post-renovation checklist covers the glass alongside everything else handed over dusty.

07What should you send to get an answer?

Four things answer most glass enquiries in Ipoh, and between them they decide whether the marks are something a clean reaches or something that is not a cleaning job at all.

1. A photograph in daylight, square to the pane. Indoors against the light hides almost everything that matters.
2. What sits above the glass. A concrete ledge, a sunshade or a render band explains most streaked marks before anyone arrives.
3. How long it has looked like this. Months and years point in different directions.
4. How high it goes, and the ground below it. Past safe ladder height this is planned work with equipment, and a facade or elevation is priced after someone has seen it.

Send them to 014-313 0767 and scope, timing and a price range come back the same way — and where a site visit is needed to quote properly, we say so rather than guessing. Kean Can Cleaning Service has been cleaning in Ipoh and across Perak since 2019, and glass is the second thing it is known for after floors.

08What else do people ask about marks on glass?

Will vinegar or a supermarket glass cleaner shift it?

On light surface soil, a mild non-abrasive cleaner is what the guidance asks for anyway. On a bonded deposit, household acids are the wrong tool: the National Glass Association's instruction is that cleaning solutions "should not include acids, especially muriatic / hydrochloric" and hydrofluoric acid, and acids are among the materials it lists as able to harm laminated glass. The risk is not that it fails, but that it works unevenly and leaves a worse mark.

Does it matter if my windows are tinted or coated?

A great deal, because razor blades "should never be used on coated glass surfaces" and a coating can be stripped without the glass itself being touched. The paper gives a simple check for one case: touch a pencil point to the glass, and "If the reflection of the pencil point meets the real pencil, the coating is exposed on that side." That finds a reflective coating on the face you are touching. It does not find a Low-E coating, which the same paper calls "typically neutral in color and very difficult to see", nor applied film — so tell us about film or tint, because it changes what may be used.

Can you tell from a photograph whether it will come off?

Often yes for the first question, whether it is ordinary soil or something bonded. Separating a bonded deposit from etched glass usually needs a tested patch on site, in daylight. We would rather do that patch and tell you the glass is damaged than take on work that cannot deliver.

09Where this comes from

• National Glass Association, Glass Technical Paper FB01-00 (2023), Proper Procedures for Cleaning Architectural Glass Products — the routine method, acids, test-cleaning and daylight inspection, the non-routine techniques and their risk, the razor-blade and coated-glass rules, construction protection, films, and the twice-yearly baseline. Updated December 2023.
• Vitro Architectural Glass, Glass Technical Document TD-107, Residue on Glass — run-off carrying contaminants onto glass, the silicate bonding mechanism and its speed, build-up over repeated cycles, masonry leaching, hard-water sprinkler residues, and when replacement is the practical remedy.

Both documents are American and are quoted and summarised here rather than reproduced; neither is a Malaysian standard. Vitro states that its cleaning recommendations are offered "for specific projects with severe residue and dirt build-up" and "should not be used as standard cleaning procedures" — it is cited here for how the marks form, not as a method to follow at home. The fingertip check in chapter 03 is our own practical guidance, not taken from either document.

Written by the Kean Can Cleaning Service crew in Ipoh, Perak — about the company.