Waterproofing Under Tile: Things You Should Know

Posted by Dean Linthicum on Oct 3, 2018 2:00:00 PM
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Things you should know when installing tilesWhen installing tile, whether it’s flooring for a restaurant kitchen, a swimming pool or a patio deck, the process should include waterproofing the substrate prior to the tile installation.

If you don’t create a seal under the tile, it may lead to costly problems down the road.

Aren’t Tiles Waterproof?

It’s a common assumption among builders that tiles are waterproof. Many in the construction business believe that once the grout has set, water can no longer pass through the tile flooring and into the substrate. Unfortunately, this isn’t true. Even when there are no visible gaps in the grout, water can migrate through the tile.

Keep in mind that some types of tiles are more susceptible to water intrusion than others

  • porcelain is denser than travertine; consequently, less water passes through porcelain tiles than their travertine counterparts, and
  • natural stone tiles, because of their porous surfaces, can absorb water, allowing moisture to travel through them and into the subfloor. 

Additionally, except for certain epoxy-based varieties, most tile grouts are susceptible to moisture absorption and transmission. Grouting does reduce the amount of moisture that goes through the tile flooring, but it doesn’t completely stop it.

The bottom line is that you shouldn’t expect tile flooring alone to prevent the intrusion of moisture. Without a waterproof sealing solution, such as CIM’s cold, fluid-applied membrane system, moisture will reach the subfloor through the thin set and tile system, thereby increasing the risk of problems. 

Also read: Waterproofing It Right the First Time Will Save You Money

Identifying the Six Most Common Tile Problems

1.    Mold and Mildew

One of the biggest problems of water trapped under tiles is the risk of mold. This situation creates the perfect breeding ground for mold, mildew, and fungi. Why is this something to avoid? According to the Centers for Disease Control and Prevention (CDC), exposure to mold increases the risk of upper respiratory tract infections, coughing, wheezing and asthma attacks. Whether it’s a residential home or commercial building, indoor mold is a serious health concern.

2.    Pest Infestations

It’s not just fungi that prefer wet and moist environments; certain pests favor them, too. If the tile flooring isn’t waterproof, moisture will seep into the substrate where it will attract common pests. You may find termites, carpenter ants and centipedes in the basement or crawlspace, all of which thrive in moist environments. And while pesticide applications may initially rid your property of the unwanted guests, they offer only temporary solutions. Unless you fix the moisture problem, the infestation will likely return.

3.    Structural Decay

There’s also the risk of structural decay when water passes through tiles. Assuming the home or building is made of a wood frame – not a steel one, moisture will saturate the studs and framing components, which can lead to rot and decay as a result of a special type of fungus that feasts on wood’s cellulose.

4.    Foundation Problems

Most foundation repair companies agree that water is the leading cause of foundation damage. When water passes through tile flooring and into the substrate, it accumulates around the substructure, setting up the perfect environment for cracking or uneven settling. Considering that foundation repairs cost thousands of dollars, this is something most homeowners and builders want to avoid.


CIM 500


Waterproofing Under Tiles Can Protect a Structure’s Foundation from Moisture-related Damage

Many problems can be avoided by applying a waterproofing system beneath the tile overburden. CIM’s “Waterproofing Under Tile” guide offers an outline for keeping surfaces dry and impermeable.

Listed below are the advantages  of using CIM 1000’s fluid-applied membrane system beneath a thin set and tile assembly:

  • high solids, low odor and VOC compliant
  • bonds to most construction materials including asphalt
  • bridges new cracks in concrete up to 1/4”
  • suitable for immersion
  • impermeable chemistry
  • liquid application that’s easy to use
  • cold application
  • UV stable
  • ICC-ES AC115
  • ANSI A 118-10-2088
  • International Building Code (IBC) approved
  • Uniform Plumbing Code (UPC) approved

Waterproofing a Shower Pan (Before & After): 



Although a quality fluid-applied impermeable membrane system such as CIM 1000 will ensure that moisture does  not permeate the membrane system into the subfloor under normal conditions, we highly advise to follow the manufacturer’s recommendation. Contact us if you have any question, 

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Topics: CIM 1000 Premix, CIM Industry, CIM Concrete Waterproofing, Waterproofing tiles

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