Specifying ceramic, glass, and stone tiles for exterior and interior wet areas

Tubs and prefabricated shower receptors should have a minimum 25-mm (1-in.) flange at their edge so the wall vapor barrier overlaps it to ensure the water travels toward the drain and avoids getting behind those receptors. Often, those receptors do not have the 25-mm flange. Either way, this author always recommends taking a bitumen flashing material, with the self-adhesive front and back, and have those transitions flashed 152 to 305 mm (6 to 12 in.) from the receptor edge to the wall, and overlapped with the wall vapor retarder.

This author also recommends flashing the inside corners of the shower framing and at the transition of shower pre-sloped dams, seats, and shelves. Anywhere there is a transition in a shower application, there is a potential for a breach allowing moisture to migrate into the wall cavity, which can result in huge collateral damages.

Per UPC and industry standards, the waterproof membrane is to extend over the face of the dam and outside the rough jambs of the shower opening at least 76 mm (3 in.). Waterproof folds, laps, and reinforcing webbing must extend at least 102 mm (4 in.) in all directions from the corner. This is even more critical in steam rooms, particularly if they will be used frequently.

Steam rooms or steam showers require even more care and protection. There should be insulation boards installed behind the low-perm vapor retarder. All transitions should be properly flashed. Movement joints should be installed at all transitions using sealants meeting the industry-required ASTM C920, Standard Specification for Elastomeric Joint Sealants, and suitable for the intended use, whether it is a regular shower or a steam room. This includes inside corner transitions at wall-to-wall, floor-to-wall, and seat-to-wall corners, at the respective outside corners, and around all penetrations.

The movement joints provide protection not only against expected movements within the structure and materials (i.e. dynamic structural, moisture, and thermal movements), but also to keep water out of those vulnerable transition areas. Steam rooms need special steam-proof doors and light fixtures, and they need to be sealed at their perimeters as well as at plumbing wall escutcheons and flanges. The acrylic, latex, or siliconized sealants do not meet ASTM C920 requirements and they do not perform well over time.

Specifying and MasterFormat
How can architects help ensure exterior decks, balconies, and showers are given the attention they need to avoid failures? It is the same old answer: write a project-specific detailed MasterFormat specification that is complete, concise, correct, and clear. In the specification it is not only important to specify the appropriate reference standards in Part 1–General and the correct products in Part 2–Products, but it is also critical to specify the key steps of the installation in Part 3–Execution.

It does not matter who is at fault when there is a problem—everyone ends up paying, either in time to defend themselves, money to fix the issue, or with their reputation. It is in everyone’s best interest to ensure installation specifications are thorough, clear, and unambiguous. The following paragraphs summarize the key content that should be in specifications for tile and stone installations for exterior decks and balconies, and interior showers.

Part 1–General Requirements

1. The key industry standards must be called out:

• ANSI A108, American National Standards Specifications for the Installation of Ceramic Tile, for surface preparation and the installation of stone, glass, and ceramic tile;
• TCNA Handbook for Ceramic, Glass, and Stone Tile Installation for specifying specific installation methods;
• Marble Institute of America (MIA) Dimension Stone Design Manual for adhered and mechanical anchored applications;
• ASTM C1242, Standard Guide for Selection, Design, and Installation of Dimension Stone Attachment Systems, and ASTM Stone Physical Property Standards for the respective geological classification of the stone being used;
• ANSI A137.1, American National Standard Specification for Ceramic Tile; and
• ANSI A138.2, American National Standard Specification for Glass Tile.

2. A specific quality assurance (QA) section needs to be prepared to verify material performance and suitability for the intended application.
3. Single-source responsibility from an installation product manufacturer should be required, and should include a minimum 10-year labor and material manufacturer warranty. The product quality required for the extended warranty is much higher, and it ensures compatibility between all products. It is also important to require a letter in writing be provided from the manufacturer, before installation, stating its products are suitable for the application.
4. Tile-installers—both setters and helpers—should be certified or verified in order to demonstrate they know and are current with industry thin-set standards (e.g. Certified Ceramic Tile Installers [CTI] through the Ceramic Tile Education Foundation [CTEF] or Tile-installer Thin-set Standards [ITS] verification through the University of Ceramic Tile and Stone [UofCTS]).

Part 2–Products

1. The specifications should be performance-based. Reference specifications only call out products meeting the minimum requirements, which are essentially the least-expensive products with the lowest acceptable level of performance.
2. Stone should meet ASTM minimum/maximum physical property requirements for their respective geological classification. Ceramic tile should meet ANSI A137.1 standards, and glass tile should meet ANSI A137.2 standards.
3. Installation products should be provided by a single-source manufacturer who provides a minimum 10-year labor and material warranty. Thin-set adhesives should meet or exceed ANSI A118.15, American National Standard Specifications for Improved Modified Dry-set Cement Mortar, for higher performance.
4. Waterproof membranes must meet ANSI A118.10, American National Standard Specifications for Load-bearing, Bonded, Waterproof Membranes for Thin-set Ceramic Tile and Dimension Stone Installation, and ANSI A108.02 requirements. Perm rate for steam rooms/showers needs to be specified. Waterproof membranes on exterior decks or balconies over occupied spaces must be a primary roofing membrane.
5. Sealants for movement joints must meet the appropriate ASTM C920 requirements for the application. They must also be installed with polyethylene backing and primers per sealant manufacturer requirements.