Can I still use a ceramic coating after its expiry date?

It is a risk. Coatings react with moisture, and over time the product can thicken, crystallize or cure unevenly, which can lead to poor bonding, streaks or high spots that are hard to remove. An unopened bottle stored in a cool, dry place may still perform, but there is no guarantee. Check that the liquid is clear and flows normally, then test it on a small, inconspicuous area before using it on the whole car. Unopened coatings should be stored sealed, away from heat and sunlight, and used before the date on the bottle.