Installation Guide

VAPOR
Why is water vapor management important?
It is important to consider that water exists as both liquid and vapor in showers, and
must be managed in both forms. The prime example of this is the steam shower. Steam
showers that are not designed to manage water vapor have caused mold growth in wall
cavities, rot in wood framing, and damage to moisture-sensitive wall coverings on the
opposite side of the stud cavities.
Do all waterproofing membranes manage water vapor?
The ANSI A118.10 standard for bonded waterproof membranes was developed to
provide a framework for determining the suitability of these products to serve as barriers to
liquid water only. As such, the standard does not include a minimum criterion to establish
the ability of products to limit vapor transmission. Thus, simply selecting a membrane that
meets the requirements of the ANSI A118.10 standard for a steam shower application
is not enough. The ability of the product to limit vapor transmission must be considered
as well.
How can I identify a waterproofing membrane that manages water vapor?
Water vapor permeance is a measure of how quickly water vapor is transmitted through a material and can be determined according to the
ASTM E96 Standard Test Method for Water Vapor Transmission of Materials. The higher the vapor permeance, the less effective a material
is at slowing vapor transmission.
There is no universal requirement for vapor permeance of membranes in the building industry. The environmental conditions (i.e., differences
in temperature and relative humidity), building materials, etc., and relevant field experience will determine the appropriate membrane
performance for a given application. The consensus within the tile industry in North America has been that a vapor permeance of 1.0 perm
or less will manage vapor effectively in showers and intermittent use steam shower applications.
The TCNA Handbook for Ceramic, Glass, and Stone Tile Installation and the TTMAC Specification Guide 09 30 00 Tile Installation Manual
specify a water vapor permeance of 0.5 perms or less for bonded waterproofing membranes used in continuous use steam rooms
(e.g., those found in health clubs, spas, etc.) when tested using the desiccant method at 100°F (38°C) and 90% RH.
Does the Schluter
®
-Shower System manage water vapor?
Schluter
®
-Systems has tested the various options within the Schluter
®
-Shower System for moisture management, including KERDI,
KERDI-DS, and KERDI-BOARD in the more aggressive conditions referenced above. The table below summarizes Schluter
®
-Systems'
recommendations for the use of these products and respective water vapor permeance values.
1
Tested according to ASTM E96, using the desiccant method at 100°F (38°C) and 90% RH
2
1/2" – 12.5 mm-thick KERDI-BOARD tested
While the water vapor permeance of KERDI-BOARD meets the water vapor permeance recommendations for continuous use steam rooms
in tile industry standard guidelines, Schluter
®
-Systems has chosen to require the KERDI-DS membrane for these demanding applications in
an effort to be conservative and provide the best possible solution for our customers.
Thus, the Schluter
®
-Shower System has solutions that provide superior moisture management for virtually any tile application.
Product Recommended Applications Water Vapor Permeance (perms)
1
KERDI
Showers, intermittent use steam showers, and bathtub surrounds 0.90
KERDI-DS
Continuous use steam rooms 0.19
KERDI-BOARD
Showers, intermittent use steam showers, and bathtub surrounds 0.36
2
The importance of water vapor management
VAPOR — The importance of water vapor management 47