Choosing terrace tiles: what should you check?

Outdoors you choose differently than indoors. A terrace tile has to give grip when it rains, withstand frost, drain water and stay colourfast in the sun. Looking at the tile, the base and the drainage together avoids the classic disappointments: rocking tiles, puddles against the facade and green deposits.

Why 20 mm ceramic for outdoors

A 20 mm terrace tile is porcelain with a water absorption below 0.5% (group BIa according to EN 14411). That figure is the reason the tile is frost-resistant: water that cannot get into the tile cannot freeze inside it either. The 20 mm thickness provides the breaking strength to lie loose on chippings or on pedestals, which is not possible with 10 mm.

Compared with the alternatives: ceramic does not fade in the sun, does not develop efflorescence from the material itself (that comes from mortar or grout), withstands de-icing salt, barbecue grease and acidic cleaners, and never needs sealing. Concrete and natural stone pavers need maintenance on at least one of those points. A 20 mm tile does weigh roughly 45 kg per m²; that counts for transport and for a roof terrace.

See the series at 20 mm terrace tiles, for example Sora (concrete-look, R11, water absorption 0.32%) and Liora (100x100 and 60x60, R11).

Slip resistance: R11 is the norm outdoors

The slip resistance class according to DIN 51130 runs from R9 (little grip) to R13 (very high grip), measured with shoes on an inclined plane. For a terrace, driveway, garden path or outdoor steps, R11 is the standard. R10 is only sufficient under a roof cover that stays dry. Around a swimming pool, where you walk barefoot, also look at the barefoot class (A, B or C): at least B, preferably C.

More texture means more grip, but also slightly more dirt adhesion. An R11 tile with a fine texture, such as Sora, is the compromise that works best in practice. Watch colour and heat too: a black tile in full sun gets so hot that you cannot walk on it barefoot; a mid-tone such as greige remains walkable.

Three laying methods, three different terraces

• Laid loose on chippings: a stabilised sub-base of crushed stone (guideline 15 to 20 cm, compacted) with 3 to 5 cm of 2/5 mm chippings on top. The tiles lie loose with an open joint of 3 to 5 mm; rainwater drains away through the joint. Benefits: no mortar, no efflorescence, a tile is replaced in no time. Point to watch: the bed of chippings has to be perfectly flat, otherwise tiles rock.
• On pedestals: adjustable pedestals on a roof terrace, balcony or waterproofed concrete slab. The tile sits raised, water drains away underneath and pipework fits under the floor. The pedestals determine the joint (usually 3 or 4 mm). Edges and wind call for an edge finish or fixing.
• Bonded to a concrete slab: for a driveway, a level threshold to the house or steps. The concrete slab is laid to a fall, the tile is bonded with double application of a frost-resistant flexible adhesive (C2 S2) to 100% adhesive contact, with a joint of at least 5 mm in a flexible, waterproof grout. Movement joints every 3 to 4 m and along the facade. A drainage mat between slab and adhesive carries water away and prevents efflorescence.

Format, thickness and method are linked: 100x100 on pedestals or on chippings is possible but takes two people; 60x60 is the easiest to handle. So decide on the method early, together with the landscaper.

Fall, edges and water

Outdoors, water must drain away, always. Guideline for the fall: 1.5 to 2% (1.5 to 2 cm per metre), away from the facade. The terrace sits lower than the threshold and gets a gutter or drainage channel on the low side.

Edges hold everything in place: a concrete kerb, an L-profile or an edging kerb with chippings; an edge profile or step tile for steps. Make skirting against the facade from the same tile, or leave it out with a strip of pebbles so splash water does not stand against the wall.

Colour, maintenance and comfort

• Light (white, ivory) shows green growth and leaf stains sooner, but stays cool in the sun.
• Dark (anthracite, black) shows limescale, dust and pollen, and gets hot.
• Mid-tone (greige, light grey, sand) shows the least and remains walkable. In practice the most chosen shade.

Maintenance: brush, clean with a pH-neutral product, occasionally use a green growth remover. A pressure washer is fine at low pressure and from a distance; never aim it at cement joints. Ceramic itself needs nothing: no sealing, no coating. Moss and algae grow on dirt on the surface and in joints, not in the tile; open joints on chippings are kept clean with a brush.

Indoor-outdoor look with the right variant

A continuous look from living space to terrace is visually strong, but you never use the same tile. Indoors 9 to 10 mm matt, outdoors 20 mm with an R11 texture in a related shade. Concrete-look lends itself best to this: indoors for example Siena or Cortona, outdoors Sora or Liora. Choose the same format (60x60 indoors and outdoors) if you want the grout lines to run through.

With a level threshold, the indoor floor is laid level and the terrace has a fall; you absorb that height difference in the first metre outdoors. Also read Concrete-look tiles for a clean interior.

Conclusion

A terrace is a combination of tile, sub-base and drainage. Choose 20 mm porcelain with R11, decide on the laying method early, provide a fall of 1.5 to 2% and choose a mid-tone if you want little maintenance. Bring dimensions, photos and the situation (ground level, roof, driveway) to the showroom in Merelbeke; there we compare grip and colour on real tiles and work out quantity and delivery in the quote.