With the proliferation of membrane products, things can get very confusing. This mat system offers crack isolation and sound deadening properties and can be installed with an adhesive or thinset; however, it is not a waterproofing product. To make the surface waterproof, a separate product and application must be used to get all three properties.

Waterproofing is easily understood; something either leaks or it doesn’t. But vapor proof, what does that have to do with waterproofing? After all if something is waterproof it is waterproof, right? Water leaks are easy to find, they always leave a trail such as a drop, trickle, stream, or occasionally, a small river. Gas in the form of moisture vapor on the other hand is much harder to detect and in some quantities, near impossible without special instruments. Both can be very destructive forces on materials used in modern building construction. With tighter building envelopes and increased use of water sensitive building products in the construction process, there is a growing need to think of waterproofing in terms of moisture management, which includes both liquid water and water vapor.

Current industry standards only address the liquid aspect of moisture management. It may be time to take another look at those performance requirements with the changes in both construction practices and newer energy requirements for code compliance. Older and less energy efficient methods of building construction would allow for drying vast amounts of moisture in a structure; that is no longer possible with the house wraps and other energy code requirements in place today. I am not sure how accurate or the basis of the statement, but one respected building science professional stated older homes were capable of dispersing hundreds of gallons of water in vapor form but with newer homes, even 10 can be a problem with tight building envelopes.

Surprisingly, in spite of millions of dollars of tile-related water damage to structures every year, very little study has been done on effective moisture management for tile installation systems. Most of the research that has been done is applicable to roofs and windows, the biggest culprits of moisture damage. Ceramic tile, given its limited use in the big picture, has not come under the moisture management microscope thus far. But, when you stop and consider that the average shower sees more moisture than a rain forest in a year, sooner or later we will get their attention. Moisture management is not only a concern in preventing structural damage. With increased use of very large tile in slab-on-grade construction in both interior and exterior applications, moisture and moisture vapor management are also coming under scrutiny. With proper selection of materials, the mechanics of tile installations are unaffected; however, the aesthetics may suffer occasionally.

As the overwhelming majority of tile and related moisture management is applicable to interior structures, we will look at those. The need for effective waterproofing and moisture management today is much greater than in the past for reasons we have already mentioned. It would be accurate to say nearly any interior tile installations would benefit from a membrane application, the exception being decorative applications.

As service levels and methods of construction are widely varied, there are very few products out there that universally work in every application. Cost and level of performance desired also impact the choice of products. Hence the reason many manufacturers offer so many different products. Under the current industry test for waterproofing products, ANSI A118.10, the test for waterproofing properties uses a column of water over a piece of membrane and it is visually inspected after 48 hours for no evidence of moisture penetration. There is no requirement for permeability. What is permeability? That is the ability of vapor to pass through a given material. All materials are permeable, even steel. There is no such thing as an impermeable material; all materials have different “perm” ratings. Under building code, a material with a perm rating of less than 1 is considered impermeable. Waterproofing products we typically use in the tile industry vary widely in permeability from as little as .04 to as much as 4 and are still considered waterproof. That means they leave no visible water on the underside of the product being tested after being exposed to a column of water several for days. Vapor may pass, there is no restriction, but actual water may not. Sounds bad, right? Not at all. This is where things get more complicated.

There may be instances where we would not want any vapor (which means minimal) penetration such as a steam shower that saw daily use. Then again, there are instances where we want a waterproof surface but it needs to breathe, such as a tile installation over concrete slab on grade in an area with a high water table. There should always be some amount of consideration given to the specific needs of an installation prior to product selection. We are not going to even attempt to address the highly complicated subject of building facades which all need to breathe. Instead, we will take a look at some common areas of application and explore some facts and fantasies.

Many manufacturers offer pre-made inside and outside corners. Field fabricating corners can be done with many products but requires exacting work. Ordering the pre-made units eliminates the guesswork of whether it will leak or not.

Tub Areas

There is no tub area where the wall cavity of a structure would not benefit from no water penetration and reduced moisture vapor transmission. Regardless of what geographical area you reside in, it is always a bad idea to drive any type of moisture into the wall cavity whether composed of masonry or wood. Bad things happen to good people when moisture is trapped in a confined space with little to no ventilation. While backer boards are unaffected by water in one manner or the other dependent on product, some allow for large quantities of moisture retention drawing water from the cement grout or in some cases, absorbent wall tile.

Ideally, tile should be installed directly over surfaces that are both waterproof and have low permeability. This can be done in several ways. Some backer boards themselves have these properties. It can also be accomplished through liquid and sheet membranes, even a few certain types of thinset mortars. An added benefit of stopping water at the surface is the overall humidity in the surrounding area will be reduced by not having to provide the air to dry out a larger mass of wall due to the thinner profile of the tile and membrane. Very few homes or commercial structures have adequate ventilation to deal with the higher levels of moisture typical in tight building envelopes. Any reduction of moisture vapor is a welcome plus to healthy air.

Steam Showers

This type of installation has gone from a blip on the radar 10 years ago to an increasingly common installation. Everything previously mentioned applies but there is now a new consideration. Steam is a vapor that will penetrate the smallest pores and certainly any open areas without a moisture management system in-place but which one to use? This is a very gray area in both waterproofing products and code. Given their relatively new popularity, there is not a long history to draw on so we must apply some basic principles. All areas of a steam shower must have an appropriate water management system. Vapor in a wall cavity is bad, and without completely covering all surfaces with the appropriate membrane, is bound to occur. Because something is waterproof, that does not make it vapor proof. If the steam shower is somewhat of a novelty item, seeing only occasional use, many waterproofing products with higher perm ratings may be up to the task.

While there is no clear guidance yet from code or the tile industry documents, common sense says the greater the use, the less permeable the system should be to avoid wall cavity damage. This may rule out the use of liquid or trowel applied systems in some instances. Many do not recommend their liquid or trowel applied products for commercial application that anticipates daily use for long periods of time. Because the steam shower is in a home and not a health club does not mean it will not see daily use. Actual anticipated use should be carefully and realistically evaluated. Make your choices wisely when working on steam showers in any setting.

Interior Floors

With exception to homes using crawlspace construction, water and overall moisture management is simpler on floors as most are able to breathe freely. When waterproofing floors the water has to go somewhere so drains are appropriate, especially in laundry rooms where hoses and connections are subject to failure. You will have no trouble talking a customer into waterproofing floors if they are one of the thousands who have had a dishwasher leak, ice maker break, or washing machine overflow. They know the expense and misery of waiting possibly months for everything to dry out so the floor can be reconstructed.

End users need to also understand the difference between nuisance waterproofing or flooding. Nuisance waterproofing means such things as spilled water, intensive mopping, or tub splashing, for which only floor protection is required. Water line breaks and overflows need the waterproofing carried up the wall to create a bowl effect as well as a place to drain. These needs can add to a costly difference.


Waterproofing systems are made to keep water from going in, not coming out. Often membranes are used mistakenly thinking it will result in a drier basement. That is not true in all but a few instances. Many membrane products have limited moisture vapor limits and may also have limited pH tolerances to remain bonded. Always ask the manufacturer what those tolerance limits are and perform the appropriate tests prior to application. Showers made over concrete floors in basements require the same waterproofing as those in above grade applications.

Liquid waterproofing and the proper thinset for submerged applications will make this future reflecting pool a problem-free focal point for years to come.


There are reasons to use a moisture management system in exterior applications in some instances. Tile or stone installed on concrete over poorly drained soil is a classic example where a membrane would be of benefit in preventing efflorescing which is otherwise assured. In exterior applications, all floors require a pitch to assure water run-off. This pitch must be under the membrane and cannot be created with thinset over the top of the membrane. If a pitch must be created, a membrane should be placed over the corrected slab so water can properly drain rather than collect in the patch material. To be effective, there also must be a place for the water to effectively drain. Retaining walls and high soil lines can obstruct needed drainage. Keep in mind, not all membrane products are rated for exterior application and may in some instances require a different bonding material for the membrane.

There are occasions when waterproofing an exterior deck is desirable to reduce slab saturation and associated effloresce by trapped water. However, adequate pitch is necessary under the membrane to assure proper drainage.

Exterior Decks

Exterior tile decks are fraught with any number of issues. Most if not all tile membrane manufacturers will not warrant their systems as the sole source of waterproofing over an occupied space. While some may be up to the challenge from a technical point of view, the margin for error in application is zero making most manufacturers gun shy of this type of installation. When used, the waterproofing must be effectively flashed into the existing structure. Rails may not penetrate the system and the water must drain somewhere. Movement joints must be correctly constructed incorporating the waterproof material. If the deck is not over a living space, the liability is not as great but the same principles apply.

Throughout this article I have replaced the terms waterproofing with moisture management. Using this terminology, we are correctly indicating that moisture in both liquid and vapor form should be managed. If we continually refer to moisture management as waterproofing, then you will most assuredly meet resistance in trying to explain the benefits of a drier tile installation in a tight building envelope. Once you can create the thought process that homes should be protected from not only floods, but excessive moisture vapor, then you will find many will embrace or certainly be more receptive the associated additional cost. You must also know and understand the products you are using to provide the protection you are offering. In the current market, a little extra income while providing your client with a healthier building is a win-win opportunity.