Granite Thickness for Stairs: Is 20mm Enough?

Cladding vs. Cantilever

Cladding (On Concrete): If you are gluing the granite onto existing concrete steps, 18mm or 20mm is perfectly fine. The concrete takes the weight. Steel Grey looks great here.

Cantilever (Floating Stairs): If the stone *is* the structure (floating steps with no support underneath), you need 30mm minimum, often laminated to 60mm or reinforced with steel rods. 20mm will snap under human weight.