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Bathroom Remodels & Waterproofing: What You Need to Know

Did you know that 7 out of 10 bathroom remodels are driven by water damage? It's true. Making sure the building envelope (the outside of the building) is watertight is paramount to a healthy and well-built home. When it comes to bathrooms, waterproofing is even more important, since just a 12-minute shower is the equivalent of 1,100 inches of rain. There are numerous ways to waterproof, but the most important thing is that it is done properly by an experienced craftsman. What do you need to know? Be aware of signs of potential leaks. I'll illustrate with a family story.

My dad's home was built in the 1950's (we moved in during the late 1970's) and it hasn't been remodeled other than flooring and paint. When visiting him at the beginning of the year, I noticed that the entry wall and backside of his primary shower, was showing water damage and mold (see photo on the left). When we did the demolition, there was significant water in the wall cavity. My guess is that the person who installed the grab bars a few years ago didn't properly waterproof the screw holes, which allowed water to seep into the wall.

After the primary shower was fixed, I was visiting again and noticed in the secondary bathtub that tile was pulling away from the substrate. Given that he enjoys having house guests, I told him that we would need to redo the entire tile surround, while attempting to preserve the amazing, original peach tub (Kohler has a limited edition Heritage Color collection that is almost identical)

When we did the demolition, we found a weed in the wall cavity (see image to the left) that was as tall as the shower head. This means there was enough moisture to allow it to grow for an extended time frame which explains why the tile on that wall was starting to pop off. The tile had been adhered directly to the drywall with no waterproofing in place. The fact that there wasn't more damage is a miracle.

Today, you'll often see cement or fibrous cement backerboard used inside a shower to adhere tile to. While it is water resistant it is NOT waterproof. It needs either a roll on waterproofing like RedGard (which is waterproof but not vapor retardent) or Schluter Kerdi membrane (which is waterproof AND vapor tight) to seal it. Fibrous backerboard can't sit directly on a mortar bed or tub deck, otherwise it will wick up water using capillary action.

Understanding that water can penetrate via gravity, capillary action and water vapor brings understanding to how to prevent water damage. My dad's primary bathroom water damage was most likely due to gravity (and the puncture holes of the grab bars), while the secondary bath was due to capillary action at the joint between the tile and tub. Now that both have been redone with Schluter (which has a lifetime warranty), by a skilled installer, he'll never be forced to do another bathroom remodel by me. If you read my blog post about the costs of my own bathroom remodel, you'll understand why I was willing to spend so much for the construction. My piece of mind was worth every penny.

Best Tech Contracting, the contractor I've used for over a decade used to use the traditional Hotmop method prior to switching to the Schluter system. Here is his take on it...

The traditional Hotmop (tar based waterproofing) on the shower pan, with concrete float.

Concrete float includes: 2 layers of 15 lb. felt paper, metal lath, scratch coat, brown coat, then set tile.

Pros - Less expensive, but becoming obsolete

Cons - (3 – 4) day process before starting tile (vs Schluter which can be tiled the same day), very heavy, time consuming, hotmop eventually cracks and leaks, messy, wear and tear on the (installers) body and holds on to moisture because of the concrete,

In doing research for this blog post, I researched videos of different methods of waterproofing and came across this channel that troubleshoots poor installations vs proper installations of various waterproofing methods. Schluter also has an extensive collection of videos on their products if you want to learn more.

If you're overwhelmed with the idea of starting your bathroom remodel, you're not alone. With my understanding of construction, I can help the process run smoother/with less headache and can help make sure the work is being done properly. Let's set up a personalized interior design consultation to discuss your needs. Please contact me at or view my services online.

Learn more tips in my free Interior Design eBook here

Always look for the Silver Lining


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