The importance of a properly waterproofed shower is sometimes overlooked when planning a remodel. Everyone always wants to make the shower look pretty and concentrate on the visual aspects of the shower. Things like glass inserts, neat little liners, listellos and mosaics, and cool little patterns that make your shower stand out from the crowd. That’s great! But, without proper waterproofing all this hard work, planning and money spent will be for naught.

Any tile installation is only as good as the substrate on which it is installed. If your shower substrates (wall and floor) are not properly waterproofed they will, over time, begin to break down, allow water deeper into the structure of the house, and/or start growing mold. The last, growing mold, is a true ‘and/or’ because whether the first two happen or not an improperly waterproofed shower will grow mold.

Mold is a simple creature. It doesn’t require much to survive and multiply. In fact it needs only two things: moisture and food. And similar to my teenage son it has the ability to consume nearly anything within reach. In most cases temperature is not a factor. Some species of mold grow in cold climates and some in warmer, the temperature simply dictates the type of mold likely to grow.

Black Mold behind a shower substrate

Black Mold behind a shower substrate

Of the two requirements moisture is the most relevant. Mold has the uncanny ability to consume nearly any organic substance and propagate so long as moisture is present. These organic materials include things such as wood, paper, cloth, even soil. If moisture is present mold can utilize nearly anything as a food source. Moisture and water control are the key to eliminating mold growth.

Water control in a shower substrate simply means that any water that gets behind your tile be directed down into the floor or basin and out the drain. Water will get behind your tile – grout and tile are not waterproof. This is a common misconception and leads people to believe that if they coat the tile with enough sealer or silicone the corners enough they can eliminate leaks – it will not work. Sealer does not waterproof tile or grout, it simply makes them more resistant to staining. Your shower should be absolutely waterproof before a box of tile is opened.

Eliminating mold growth is a key factor to a properly functioning shower. Mold has the potential to cause health problems like allergies, lung problems, …I’m gonna stop there because it gets really nasty. Suffice it to say that mold has the potential to be very dangerous. In fact, the minimum requirements suggested by the EPA for mold removal are an N-95 respirator, gloves and goggles. That means that when I tear out a mold-infested shower I look like Darth Vader.

You can never eliminate mold spores. Mold spores are the dormant form of mold or ‘seeds’ if you will. They are completely harmless, and they are everywhere – even floating around in the air. Without moisture, however, they will never begin to grow and multiply – just like a seed. You can not control the spores – you can only hope to contain them!  Obscure SportsCenter references aside, mold spores without moisture are about as dangerous as dust.

Once these mold spores come in contact with moisture, however, they begin to feed and multiply – exponentially. That’s just a big fancy math word that means really, really fast and in great numbers. This does not require much moisture at all. Think about mold on bread. Now that’s a fairly harmless mold but it also requires moisture and a food source. The food source is, well, self-explanatory. The moisture usually is only the small amount of condensation inside the plastic wrapper or even the moisture evaporating from the bread! Think about that – moisture evaporating from the food source to propagate mold. If bread doesn’t last, your shower, into which you dump gallons of water per day, doesn’t stand a chance.

Mold feeding on drywall and mastic

Mold feeding on drywall and mastic

A properly waterproofed shower eliminates both requirements for mold growth. While moisture inside a shower obviously cannot be eliminated it can be controlled and properly channeled. Some methods are more efficient at doing this, but every proper method will flush water through and replace it with new water. If there is water remaining in your shower substrate after use it will be flushed through and replaced with each use in a correctly built shower. If there are any mold spores that have begun to grow between uses they will be flushed out with the water. It will never have a chance to fully propagate and wreak havoc.

A food source, on the other hand, can be mostly eliminated in your shower substrate. Materials such as cement backer boards are not a viable material for mold to feed. Any soil or contaminants on these backer boards, however, may be enough to start mold growing. I’m talking about microscopically-sized material, nothing you would ever be able to see with the naked eye. While some of this may exist it will never cause enough of a problem with mold so long as the moisture in your substrate is properly channeled.

It all goes back to water, doesn’t it? Mold is like a plant (a fungii, to be exact). Dehydrate it and it will die. Mold will release spores which consume whatever they are growing on as long as moisture is present. Are you catching a theme here? A fully waterproofed shower simply means that water is fully contained inside the shower structure and cannot spread to any area beyond the substrate perimeter. A correctly waterproofed shower also means that any water inside that perimeter is flushed and replaced with each use – there is never an area in which water is left standing or dormant. This is a very important factor.

Mold feeding on wooden structure

Mold feeding on wooden structure

A fully waterproofed shower can still grow mold. A correctly waterproofed shower can not. If the spores are not flushed through with each use they can still remain in the shower and begin to propagate. A correctly built, full system is required to eliminate mold inside a shower substrate. In this context a ‘full system’ simply refers to a shower built in a way that does not leak, correctly eliminates any standing water and controls water in a way which always channels it into the drain.

There is way too much information about mold to stuff into one little post. For very detailed (scary) information you can visit the EPA’s mold information page. From that page you can access literally thousands of pages of technical information about mold and how it grows – more than any normal sane person would need. Simply by reading this post you should score 100% on their basic pre-test. Really, try it HERE. I’ll wait…

See, you’re already one up on everyone else – well done.

When you spend all that money on the perfect tile, all that time on the perfect design, and all that time dreaming about what your new shower will look like, be sure to spend some time on ensuring all that will last. The most important part of a properly constructed shower is the part you will never see.

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