This is the question that causes the most disappointment after a job. The glazing was cleaned properly, and yet a white haze remains. The reason is simple, and deserves explaining before rather than after: past a certain stage, a limescale mark is no longer dirt sitting on the glass — the glass itself has changed.
Where limescale on glass comes from
Water contains dissolved minerals. When a droplet evaporates on glass, the water leaves and the minerals stay. Repeat that thousands of times and you have a deposit.
The most frequent sources in Belgium:
- Automatic irrigation and garden sprinklers hitting a glazed bay. The number one cause of milky façade glazing.
- Run-off from a sill, ledge or cornice in stone or concrete, which loads the water with minerals before it runs down the glass.
- Hard water splashes in kitchens, bathrooms and glazed showers.
- Repeated condensation always drying in the same place.
- Mortar or cement from a building site, diluted by rain — particularly aggressive.
Three stages, and what can be done
Stage 1: recent, surface deposit. The haze sits on the glass, visible against the light, sometimes felt with a fingertip. Expected outcome: careful cleaning removes it, possibly with a local acid treatment. The most common and most satisfying case.
Stage 2: old, baked-on deposit. Limescale has built up in layers and bonded to the surface. It resists routine cleaning. Expected outcome: a specific treatment can markedly improve appearance. It takes time, a suitable product, sometimes gentle mechanical work, and carries a risk to assess per glazing type. The result is real but partial and not guaranteed. This is priced separately from a clean.
Stage 3: etched glass. The deposit has attacked the glass surface. There is nothing left to remove: the surface is pitted and dulled in depth. Expected outcome: no cleaning removes it, because there is nothing to remove. Only glass polishing processes — another trade, with its own risk of optical distortion — or replacement change anything.
How to tell the three apart yourself
A simple test before requesting a quote:
- Wet the affected area with water.
- Look at it while it is wet.
- The mark disappears under water → a surface deposit. Cleaning has a good chance. (Stages 1 and 2.)
- The mark stays visible even wet → the glass surface is altered. No cleaning will remove it. (Stage 3.)
The test is not infallible, but it prevents a lot of false hope. Send a photo of the dry area and one of it wet: it is one of the most useful pieces of information we can receive.
What not to try yourself
- Steel wool or abrasive pads. They scratch glass permanently, and scratches show far more than limescale.
- Undiluted strong acids. They attack glass, seals, silicone, aluminium and surrounding stone. A damaged seal costs more than the cleaning.
- Rubbing hard with vinegar on an old deposit. It helps on fresh deposit; on baked-on scale it does little and encourages scrubbing, hence scratching.
- A blade scraper on toughened or coated glass. Some glazing has a surface coating a blade will tear off irreversibly.
- Treating in full sun. The product dries before it acts and can mark.
Prevention is where it is won
- Redirect sprinklers hitting the glazing. Free, and the single most effective measure.
- Deal with the cause of the run-off. A sill or cornice discharging onto glazing will always produce deposit.
- Shorten the intervals on exposed glazing. Young deposit comes off; five-year-old deposit often does not.
- Hydrophobic treatments applied to glass exist and reduce deposit adhesion. Their duration is limited and variable, and they do not replace maintenance.
Our position
We say before the visit what we think we can remove and what we do not think we can, based on photos and on-site inspection. We do not bill a limescale treatment as if the result were guaranteed, and we do not promise to restore etched glass. Less appealing than a guarantee, and more useful.
FAQ
My windows have been milky for years. Any hope? Do the water test. If the mark disappears under water, yes, at least partly. If it stays visible when wet, the glass is etched.
Is limescale treatment included in a clean? No. It is longer work with different products and no guaranteed result. It is priced separately.
Does pure water remove limescale? No. It avoids depositing new scale, which is very different from removing an existing deposit.