Before you try anything: always speak to a professional before cleaning, treating or applying any product to your stone. Every slab is different, and the wrong product can cause permanent damage. Contact us or a qualified stone restorer first.
Quick answer
Limescale on onyx has to be removed without acid, because descalers that dissolve it will also etch the stone. Soften the deposit with warm water and pH-neutral cleaner, then shave it off carefully with a new plastic razor blade held flat. Heavy build-up is a job for a stone restorer.
First, check what you are dealing with
- Chalky white crust you can feel: limescale. Follow the steps below.
- Smooth dull patch with no crust: etching, often from past descaler use.
What you need
- pH-neutral stone cleaner
- Warm water
- New plastic razor blades
- Microfibre cloths
Step by step
Soften the deposit
Lay a cloth soaked in warm water and pH-neutral cleaner over the scale for 10 minutes.
Shave it off
Hold a new plastic razor blade almost flat and gently push under the scale. Keep the onyx wet as you go.
Repeat and dry
Re-wet and repeat until the crust is gone, then rinse and dry thoroughly.
Check for etching
If the area underneath looks dull, it has probably been etched by past descaler use. See fixing etching.
What not to use on onyx
- Vinegar, lemon juice or "natural" citrus cleaners: they etch onyx.
- Scourers, steel wool and abrasive creams on a polished surface.
- Mixing cleaning chemicals, especially bleach with anything else.
- Bathroom descalers, CLR, vinegar and lime removers.
- Metal razor blades and steel wool.
When to call a professional
If scale is thick or has been there for years, a restorer can remove it with stone-safe products and re-polish any etching underneath. Onyx needs a restorer who works with it regularly: it is softer and more fragile than marble and easy to over-polish.
Understanding hard water and limescale on onyx
Onyx is calcite and usually highly polished, so a drop of lime or wine leaves a dull etch that catches the light immediately.
On polished, often backlit onyx, etches and scratches are visible from far away and light shines through any change in the surface.
Onyx needs a restorer who works with it regularly: it is softer and more fragile than marble and easy to over-polish.
Good to know
Onyx vanities and bars are very sensitive to descalers. Keep scale away by drying after use, and leave build-up to an onyx specialist.
Stop it happening again
Whether yours is honey, white, green and pink banded onyx, often backlit, repairing it fixes today's mark; protecting it stops the next one. Our clear Stone Protection Film sits over the surface, so acids cannot etch it and liquids cannot soak in. Onyx is usually polished, so Gloss film is the natural match and keeps its reflective depth. It is installed across Sydney with a 10-year written warranty.
How we protect onyx · Cleaning natural stone · Hard water & limescale on every surface