2024-25_NTCA_Reference_Manual_dig_dwnld

Loss of Bond

Bond failure on exterior installations

Problem

Cause

Cure

Tile comes off clean, or with a small residue of dry-set mortar where ridges in dry-set mortar were in contact with tile.

Full coverage not obtained between dry set mortar and tile, or dry-set mortar and substrate. Water penetrates and collects in voids, and upon freezing, forces tile to lose bond. Condensation can occur within voids.

Troweling of mortar in one direction, fully collapsed mortar ridges and at least 95 percent coverage must be obtained between tile, dry-set mortar, and substrate in accordance with ANSI A108.5 on exterior installations, which requires 3/32 in. (2.4 mm) minimum thickness of bonding material and proper bedding. Consider setting method F111 of TCNA Handbook . Adhere strictly to TCNA Handbook method EJ171, and to ANSI Specifications A108.01-2.1.5 Movement Joints. If details on plans or specifications do not call for expansion joints, the architect should be notified of the ANSI Expansion Joint Requirements. If the architect still does not specify expansion joints, the tile contractor should initiate a letter of release of liability. The tile contractor should not assume responsibility for the design and location of expansion joints. Also, use a modified or improved dry-set mortar to assist in bonding when slight thermal movement is anticipated. Notes: 1. Polymer modification is required for all exterior mortar installations unless other requirements are specified by manufacturers of other components in the system. 2. Exterior installation with epoxy should be done only with written approval of the selected materials manufacturer.

Failure will occur at the weakest point. Sometimes, entire sections of tile will crack and/or arch away from substrate. If expansion or contraction occurs during the curing cycle of the dry-set mortar, bond failure may occur within the matrix of the dry-set mortar. If curing of the dry-set mortar is complete and a good bond is obtained, failure will occur at the weakest interface, i.e. either at the substrate or at the tile.

Lack of movement joints. Heat or cold, causing expansion and contraction of tile and substrate, create pressures that overcome the bonding strength of the setting material.

NTCA Reference Manual | 2024 / 2025

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Chapter 8 | Thin-Bed Method Installations