technical

Large-format tile specification & installation

Introduction

Design professionals continue to specify larger-format tiles as manufacturers continue to expand their size offerings. The newest introductions have been 16x32, 16x48, 18x36, 24x48 and 36x36. Large formats provide an open and monolithic aesthetic, easier maintenance and a thick, slab-stone look with an easier-to-install and transition 3/8”-thin porcelain tile. The stone look is further enhanced by the availability of multiple finishes: natural, honed, semi-polished, polished and textured. As tile sizes are increased, however, special consideration should be given to substrates, bonding materials and layout.

Substrates

Specification and use of self-leveling underlayments, such as C-Cure’s LevelCure 950 & 951, are the most efficient way to attain the uniformly flat substrates (1/8” variation in 10’) required for large formats. These products are cement-based and may be poured or pumped onto the slab. Use of crack-isolation systems prevent migration of shrinkage cracks from the substrate to the tile. These membranes are available as sheets, roller or trowel-applied liquids and as one-step mortars.

Bonding materials

The use of medium-bed mortars and large trowels (1/2” square notch or 3/4” rounded notch) help ensure adequate mortar coverage for large format tiles. ANSI standards call for these latex-modified performance mortars to be back-buttered to the tile and combed over the substrate in parallel ridges. The tile is then pressed in perpendicular to the comb marks to achieve full coverage. When installing large formats on walls, use non-sag mortars, spacers or other temporary holding devices to prevent slippage.

Layout

Large-format tiles are also rectified and can be installed in patterns and with thin “credit card” joints. In general, ANSI recommends that grout joints be at least three times the tile's facial variation, so a rectified tile with a facial variation of +/- 1/32" would require a minimum joint width of 3/32". Consult your distributor representatives and your installation professionals to obtain project-specific recommendations on joint size, layout, crack-isolation systems and expansion joints.

Large rectangles, for example, normally exhibit some warpage even while conforming to ANSI standards. To minimize lippage an architect would specify a stack bond pattern rather than a running bond – or increase the joint size.

Most interior installations require a 1/4” expansion joint every 20-25’. As an alternative, a 1/8” soft (flexible) joint would be required every 10-12.5’.

Conclusion

This is intended to be a general introduction to large-format tile specification and installation. You will find manufacturers of installation products and the Tile Council of North America (TCNA) to also be excellent resources. We have included a link to TCNA publications below.

TCNA Publications