by Dr. Fred Hueston
Stone Forensics

James I. Medina
Director of Architectural & Contractor Services, Noble Company

Noble Company Waterproof Membrane

Noble Company Waterproof Membrane

The “perm rate” is a measure of the permeability of a material, indicating how much moisture or water vapor can pass through it. When it comes to choosing a waterproofing system for a shower installation, the perm rate is an essential consideration. It plays a crucial role in maintaining the integrity of the shower structure and preventing potential issues such as water damage, mold growth, and deterioration over time. Here’s why the perm rate is important in this context: 

Waterproofing Efficiency:
The primary purpose of a waterproofing system in a shower is to create a barrier that prevents water from seeping into the underlying building materials. A low perm rate ensures that the waterproofing membrane or material is highly resistant to water penetration, effectively protecting the structural elements of the shower and the surrounding walls from moisture damage. According to ANSI 118.10 (B), a low perm waterproofing membranes is tested to the ASTM E96 procedure E. The water vapor permeability must be below .5 perms. This test is at 100° F and 90% relative humidity. 

Moisture Management:
Bathrooms and showers are high-moisture environments, and water vapor can build up from regular use. If the waterproofing material has a high perm rate, it may allow some moisture to pass through, leading to potential moisture accumulation behind tiles or within the wall cavity. Over time, this can result in mold growth, decay, and compromised structural integrity. 

Many installers and homeowners do not realize the unbelievable arch in performance of waterproofing membranes on the market today. Some meet low perm standards, while others do not. Some membranes have perm rates as high as 3.5 while others are as low as .15. 

Durability and Longevity
: A waterproofing system with a low perm rate tends to be more durable and long-lasting. It can withstand prolonged exposure to water and moisture without degrading or losing its effectiveness. On the other hand, a high perm rate material may degrade over time due to constant exposure to moisture, necessitating premature replacement or repairs. 

When constructing with sustainability and product longevity, often little to no attention is given to the products that lay beneath the finished floor that are designed to protect the installation and contribute to the life of the project. As an example: A Porcelain tile has a life of 50 to 80 years, but it is only as durable as its substrate. Does it make much sense, if a product that only lasts 10 to 15 years is installed to protect it? When considering durability and longevity, the entire assembly must be considered. 

Complementing Tile, Grout and Drain:
Even though the waterproofing system serves as the primary defense against water, it is essential to consider that tile and grout are not entirely waterproof. They may allow some water penetration. Therefore, having a waterproofing layer with a low perm rate provides an additional layer of protection, reducing the risk of water reaching vulnerable areas beneath the surface. 

The overall assembly in any waterproofing installation should be considered. The water-in, water-out method. If an installation is in a shower and the pan is mudded, the water should be designed to go through the grout and through the mud to the drain above and below the installation. But there are methods of waterproofing that are on the surface of the mud. Remember that the connection to the drain is critical. With the water in-water out method, you must consider weep hole protection which will allow a means of egress to the water in the system. With a surface waterproofing method, the attachment to the drain is slightly different. It may be bonded to a drain flange or under a clamping ring. Either method works, but having an understanding on the connection is critical before the installation starts. 

Building Code Compliance
: Many building codes and regulations require specific perm rates for waterproofing materials used in shower installations. Ensuring that the chosen waterproofing product meets or exceeds these requirements is crucial for compliance and may be necessary for insurance coverage. All manufacturers give recommended installation methods. These methods will supersede the TCNA minimum standards. It is important to note that if products are not installed per the manufacturer’s recommendation, the manufacture will void the warranty. When installing waterproofing sheet membranes, the manufacturer will require a 95% plus coverage on the bond coat! For manufactures of liquid waterproofing membranes, the manufacturer will require the product be put on at a minimum mil thickness. These may seem like minor line items, but I assure you they are not if the matter goes to court. 

The perm rate is a critical factor when selecting a waterproofing system for any wet area or shower installation. Choosing a material with a low perm rate will help ensure the long-term effectiveness and durability of the waterproofing, protecting the structure from moisture-related problems and maintaining a safe and functional shower environment. Always consult with a professional or follow manufacturer guidelines to select the appropriate waterproofing system for your specific shower installation needs.

Frederick M. Hueston is a respected scientist with a rich background and extensive expertise in the stone and tile industry. Growing up in a family deeply involved in the field, Frederick’s early passion drove his educational journey, resulting in a degree encompassing biological, chemical, and physical sciences. Combining academic knowledge with practical experience, he authored 40+ books and 200+ articles covering various stone and tile topics. His publications range from installation techniques to restoration methods, solidifying his reputation as a revered authority. Founder of StoneForensics, Frederick established a leading firm offering inspections, analysis, and consulting. Recognized for his contributions, he stands as a distinguished figure in the industry, continually advancing the field’s scientific principles and practical applications to drive excellence.

James I. Medina’s background in construction stems from over 30 years in the industry. Starting out as a tile contractor he later worked with a general contractor in Las Vegas as a Project Coordinator and Project Manager. Wanting to understand large commercial projects he worked with Mirage Properties in 1998. The management took note of his potential and brought him over to develop the Wynn properties. In 2004, while working for Wynn Design and realizing that flooring was his true passion, James earned his certification in Flooring Forensics. This gave him a different outlook on every project and approach to installations. This unique insight of why floors fail in residential, commercial, and hospitality helped James to analyze and solve some of the most perplexing failures. His mission is to educate design professionals on the current and future approaches to the changes in the industry and to find out the answers to why installations fail.