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Large Porcelain and Glass Bodied Tiles

Problem

Cause

Cure

Any of the following may cause problems with large porcelain and glass bodied tiles. Inadequate contact between mortar bond coat and backs of tiles, which may be caused by improper beat-in and using inadequate amounts of mortar, or worn or improper trowels.

Any of the following may be a cure to problems with large porcelain and glass bodied tiles. To secure good contact between tiles and ribs of latex-Portland cement mortar, tiles must be pushed and slid into the mortar using the NTCA Trowel and Error method for bedding tiles. Flat back-troweling tiles with a thin, flat coat of latex-Portland ce ment mortar helps develop a better bond to the tile. On large format tile, a box screed has proven to be an excellent means of controlling the amount of mortar applied to the back side of large tiles. Latex-Portland cement mortar applied to the substrate should be troweled out evenly in one direction – not swirled – with notched trowels. Ribbed mortar on only one surface helps reduce voids and air pockets. This method also produces a smoother, more even surface than con ventional flat back-troweling, which often leaves tiles with excessive lippage. Successful installations of large porcelain and glass bodied tiles require the use of a manufacturer’s recommended latex-Port land cement mortar that meets or exceeds ANSI specifications. Use latex-Portland cement mortars that are more flexible, in addition to having superior bonding capability. Latex-Portland cement mortars bond large porcelain tiles and tiles con taining glass in the body, better than more conventional mortars. Mortar flexibility helps bridge stresses created between substrates and large, unforgiving tiles, reducing possibility of tiles shearing off. Check with manufacturer for exact prod ucts recommended. Press and slide tiles into position using the Trowel & Error method for bedding tiles ( See page 206 ). Check to see that uniform contact is being achieved at corners, edg es, and the back of the tiles by pulling tile

Loss of bond between bond coat and large porcelain tiles or tiles containing high percentage of glass in the body. Tiles may come off mortar bond coat clean, even with full coverage on backs of tiles.

Use of pure cement bond coat over plastic mortar beds.

Use of dry-set mortar without latex ad ditives.

Presence of excessive white powder (manufacturer's release agent) on back of tile.

Bending or deflection of substrates.

Differential expansion between tile and setting material.

Working on or too early traffic on newly laid tile floors.

Shrinkage or setting of substrates due to changes of moisture in structure or movements in the structure after con struction is complete.

Improperly engineered structure for the installation put into place.

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NTCA Reference Manual | 2024 / 2025

Chapter 5 | Material Specific Products and Installation