Waterproofing For Your Shower; What You Should Know
Shower waterproofing is the single most important part of any tile install to have done correctly. Bad prep for a backsplash could result in an unsightly install, on floors it could cause cracking tiles and grout, but on a shower it can and often does result in leaking, dripping ceilings, hidden mold and bathroom renovations that could run tens of thousands of dollars on an otherwise acceptable installation. So how do these systems work, how can they be repaired, if at all, and what should you look for when you’re hiring a professional to remodel a shower?
There are two broad categories of waterproofing being used in Michigan today, and if your house is thirty years old it likely features one of those systems currently. The first and oldest is a water in, water out liner system. These systems work by first installing a PVC pan liner, then a sloped mortar bed, and then some style of waterproofed backerboard on the walls. Once this system is in place, it is ready for tile. The second style that you will widely see I would generally refer to as a topical waterproofing system. There is far more variety to the different products that would fall under this classification, but generally speaking a topical waterproofing system works in a very intuitive way: the walls and shower pan (whether custom mortar pan or a prefabricated foam pan) are all coated in a water impervious membrane without any break in the waterproofing enclosure. Tile is then adhered directly to the waterproofing, hence a “topical” waterproofing application. So, which one should you consider installing, and what issues should be looked for during the installation?
Water in, water out installations
Let’s start with the strengths of this system. Despite being the older system, or perhaps because of it, this system is largely falling out of practice. However, the thick PVC liner, if you fold the corners or are experienced in using the PVC cement required to seal any cuts you might put in a corner, is very tough and durable. Additionally, if a floor tile is damaged or floor grout removed and replaced, the fact that it is underneath a thick concrete pan means that it is much harder to accidentally damage the PVC when making repairs. The walls as well are often made of either a mortar and mesh or a sturdy cement board, and while these are often covered in a liquid applied waterproofing to discourage any moisture traveling through to the wooden studs, it is both easier to repair and less likely to cause a leak while removing tiles or grout. However, the advantages quickly pale when compared to the weaknesses of the system, as well as the relative disadvantages compared to a topical waterproofing system. The most common mistake that I see with the water in water out system is a lack of a “preslope”. When constructing the pan, the liner must have a drainage slope installed below it. However, this adds a lot of time as well as additional thickness to an already thick mortar pan, and many tilers, especially those working on new houses, will omit it entirely. This can cause the mortar shower pan to retain moisture and fail to drain, making it a good environment for mold to fester unseen, and the excess moisture can degrade the grout over time. Sometimes the excess moisture in the pan can also wick up the mortar on the curb and seep onto the wooden subfloor outside the shower, harboring more mold or even rot. The second common issue is improperly installing the wall panels; often times people will use a hardiboard tile backer and bury the bottom of the panel in the pan, and the absorbent wood fibers in the hardiboard will also wick up the moisture and transfer it onto the wooden framing, causing rot and mold.
Topical waterproofing systems
Topical waterproofing systems have many strengths when compared to a water in, water out system. The first is cost. While not all systems are cheaper, the schluter system or a go board system are significantly cheaper, mostly due to the fact that your installer can use a prefabricated shower pan, reducing the labor component of floating a mortar bed and a preslope. Second, the system operates with a waterproof skin over the entirety of the tilable substrate, and when properly installed this allows for unparalleled leak protection. Lastly, the only two parts of this installation method that retain water are the thinset mortar used to adhere the tile to the waterproofing, and the grout. This means that this system retains far less moisture than a mortar pan, and can more easily dry out between uses, resulting in a cleaner bathroom and lower likelihood of mold growth. Lastly, it is much easier and safer to install a curbless shower with a topical waterproofing system, and it requires less work to adequately lower the framing to accommodate the pan that needs to be installed.
Although I consider the topical waterproofing the superior (and by far the most popular) shower system, it is not without its downsides. The most risk comes from improper installations, which may result in unintuitive failures. Firstly, some liquid applied membranes, which seem to be user friendly, can create leaks when applied to thick to a corner, or it may not immediately be obvious that all joints need a seam tape for durability under movement. Small pinholes can also go unnoticed, which can either cause large leaks or small ones that allow mold and rot to slowly spread underneath the tile. Membrane systems are better and are less prone to these errors, but the common means of seaming sheets of waterproof membrane together can cause moisture wicking if the wrong thinset is used. These thin sheets are also vulnerable to cuts and punctures during the install, and the floor should always be protected while work is occurring to mitigate the risk of an unnoticed perforation that could compromise your shower.
Besides this basic overview of the pros and cons of these two systems, there is much to learn about how to install these correctly, and when done right, both can be long lasting and durable methods for putting together your dream bathroom. If you’re planning on tackling a DIY project, then there are many great resources on helping you through the steps: research them thoroughly and make sure you plan correctly, as this is the most crucial step to your project! If you’re hiring a contractor, don’t request they use a system that they’re not comfortable or experienced in installing, as there are many methods to learn and not every tiler knows the ins and outs of each. Thanks for reading!
