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
Small chips in onyx are filled with a colour-matched epoxy or knife-grade stone filler, left to cure, then shaved flush and polished. For visible edges and anything larger than a fingernail, a professional repair is much harder to spot. Cracks should always be assessed first.
First, check what you are dealing with
- Small piece missing from an edge or corner: chip.
- Line running across the surface: crack. Have it assessed.
- Hollow sound or movement: possible structural issue.
What you need
- Colour-matched filler or repair kit
- Masking tape
- Single-edge razor blade
- Isopropyl alcohol for cleaning
Step by step
Clean the chip
Clean with isopropyl alcohol and let it dry completely.
Mask around it
Tape around the chip to protect the surrounding surface.
Fill slightly proud
Mix the colour-matched filler and fill the chip slightly higher than the surface.
Cure and shave flush
Once cured, shave the excess flush with a razor blade held flat.
Finish
Polish the repair to match, or have a restorer finish it. Onyx needs a restorer who works with it regularly: it is softer and more fragile than marble and easy to over-polish.
What not to use on onyx
- Superglue on visible areas: it yellows and does not match.
- Filling a crack without knowing why it cracked.
When to call a professional
Get a professional for sink cut-outs, visible edges, anything larger than a fingernail and any crack. Onyx needs a restorer who works with it regularly: it is softer and more fragile than marble and easy to over-polish.
Understanding chips and cracks on onyx
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 is brittle, so chips can come with small cracks. Have an onyx specialist check the piece is stable before filling.
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. It will not stop a heavy knock from chipping an edge, but it protects everything else.
How we protect onyx · Choosing benchtops · Chips & cracks on every surface