It’s one of the first questions people ask when they plan a floor that runs from inside to out. The short answer: 9–10mm porcelain is for inside, and 20mm porcelain is for outside.
9mm porcelain: made for interiors
Standard porcelain floor tiles are around 9–10mm thick. Fully bonded to a flat floor with tile adhesive, they’re incredibly hard-wearing, work well over underfloor heating and come in the widest range of sizes, including large formats and slabs.
20mm porcelain: made for outside
20mm porcelain paving is twice as thick and much stronger. It can be laid on a mortar bed like traditional paving, or on adjustable pedestals for roof terraces. Outdoor versions usually have a textured finish for grip in wet weather, and they’re frost-resistant.
Can I use 9mm porcelain outside?
Sometimes. Some manufacturers allow 9mm tiles to be fully bonded to a concrete base outdoors, as long as the tile is frost-resistant and has a suitable slip-resistant finish. For most patios, terraces and paths, 20mm is the better and more forgiving choice.
Matching the two
Many collections are made in both thicknesses in the same colour, so the floor looks continuous from the kitchen to the patio. The outdoor version is usually more textured, so order samples of both to see them side by side.