2024-25_NTCA_Reference_Manual_dig_dwnld

Dry-Set Mortar Installations

Introduction

This guide addresses factory-prepared dry-set cement mortars, modified dry-set cement mortars and improved modified dry-set cement mortars only. This guide is intended to offer possibilities for causes, character istics of those causes, and prevention of dry-set mortar cement mortar problems, and is to be used with the judgment and expe rience of all individual installers. In all cases, users should refer to the manufacturers for their requirements and recommendations on the causes, character istics, and prevention of dry-set mortar problems. The specific causes listed are common, but do not necessarily represent all problem areas. Reference to proprietary products does not imply knowledge of compliance or non-compliance with industry methods, stan dards, specifications or codes. This guide’s reference to “Loss of Bond” concerns failures using dry-set cement mortars, sanded and unsanded; but the causes and characteristics also apply to modified dry-set cement mortars, im proved modified dry-set cement mortars and EGP latex-portland ce ment mortars. Information on “Modified Dry-Set Cement Mortars and Improved Modified Dry-Set Cement Mortars” is provided to deal with those conditions indigenous to polymer modified dry set mortars . Information on EGP Latex-Portland Cement Mortars is provided to deal with those conditions indigenous to latex portland cement mortars designed for bonding to exterior grade plywood. There is also information on “Exterior Installations” that covers special conditions encountered relative to climate. In this guide, the assumption has been made that a bond failure has occurred, and offers suggestions for the causes of bond fail ure by offering common characteristics exhibited when specific causes are encountered. NOTES 1. For the purpose of this guide, the term "plaster" will refer to Portland cement plaster or gypsum plaster. 2. Injection rebonding systems have been developed using epoxy and latex modified mortar. These systems provide a potential solution to some bond failures, however, they should be used only on the recommendation and specific application instructions of the manufacturer. 3. LARGE AND HEAVY TILE (LHT MORTAR) – Large and heavy tile (LHT mortar) was developed for the installation of larger sizes of ceramic, marble and granite type tiles. They are also recommended for the bonding of tiles with a more than average variance in thickness or warpage.

The minimum thickness of 3/32 in. (2.38 mm) of dry-set cement mortar be- tween tile and substrate, after proper bedding, is specified in ANSI. LHT dry-set mortars or LHT bed modified cement mortars shall be used as cementitious bond coats from 3/16 in. (2 mm) to 3/4 in. (19 mm) thick after the tile is embedded. Unless a mortar (thick) bed method is employed, the use of an LHT mortar is mandatory when setting tiles with ungauged thickness or when both of the following conditions exist: • setting tiles with at least one side greater than 15 in. (381 mm) • where the final embedded thickness of the mortar will exceed 3/16 in. (2 mm) under the tile or stone. LHT mortar should be considered with heavy tiles to minimize slump. LHT mortars are designed as direct bond adhesives and are not intended to be used in truing or leveling underlying substrates or the work of others. All substrate tolerances must be within industry standards. It is recommended that irregularities in the substrate greater than 1/8 in. (3 mm) out of plane in 10 ft. (3 m) be addressed with trowel applied or self-leveling underlayments prior to setting the tile. The method used to compensate for substrate irregularities should be determined and specified prior to bid. Contact mortar manufacturers for special installations LHT mortars are intended to provide some additional thickness over standard dry-set mortars for tile irregularities. However, caution should be exercised in their use. Their increased thickness does not assure the installer of specified coverage nor the end of lippage problems, particularly on large size tiles. The practice of lifting tiles occasionally to check coverage should be observed. It should be noted that prying up tiles to check coverage while the mortar is still wet distorts the setting material and can exhibit a perception of better coverage than is actually being achieved, especially with larger unit tiles. It may be necessary to delay grouting of tiles installed with LHT mortars to allow for longer mortar curing time. 4. The uses of modified cement mortars are similar to those of dry-set mortars. Latex (or polymer) additives used in dry set cement tile setting mortars are designed to improve adhesion, reduce water absorption and provide greater bond strength and resistance to shock and impact. These additives allow some latitude in time, working conditions, and temperatures. Therefore, modified dry-set cement mortar is required for the installation of large format porcelain bodied tile unless other requirements are specified by manufacturers of other components in the system.

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NTCA Reference Manual | 2024 / 2025

Chapter 8 | Thin-Bed Method Installations