How To Prevent Mold Growth In Shower

One of the most important aspects of tile installation in one of the key areas of your home; is the bathroom, and specifically the shower. It’s here where extreme moisture is most common and where the presence of mold can become a problem. How do you safeguard your property and, ultimately, your health when waterproofing your shower? Here you will learn how to prevent mold growth in the shower.

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 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 true and/or because an improperly waterproofed shower will grow mold whether the first two happen or not.

Mold is a simple creature. It doesn’t require much to survive and multiply. It needs only two things: moisture and food. And similar to my teenage son, it can consume nearly anything within reach.

In most cases, the 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.

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 wood, paper, cloth, and 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 behind your tile is directed down into the floor or basin and out the drain. Water will get behind your tile as 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 in the corners enough, they can eliminate leaks – it will not work. Sealer does not waterproof tile or grout, and it simply makes them more resistant to staining.

Your shower should be waterproof before a box of tile is opened.

Eliminating mold growth is a key factor in a properly functioning shower. Mold can cause health problems like allergies, lung problems, etc.

Suffice it to say that mold has the potential to be very dangerous. The minimum requirements suggested by the EPA for mold removal are an N-95 mask, gloves, and goggles.

How Mold Growth in the Shower?

You can never eliminate mold spores. Mold spores are the dormant form of mold or seeds. 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. You can not control the spores – you can only hope to contain them! Mold spores without moisture are about as dangerous as dust.

However, once these mold spores come in contact with moisture, they begin to feed and grow. That’s just a big fancy math word that means 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 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 the bread doesn’t last, your shower, in which you dump gallons of water per day, doesn’t stand a chance.

You can visit the EPA’s mold website for very detailed information. You can access thousands of technical information from that page about mold and how it grows.

How To Control Moisture in Your Shower

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, but every proper method will flush water through and replace it with new water.

If water remains in your shower substrate after use, it will be flushed through and replaced with each use in a correctly built shower. If any mold spores 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.

On the other hand, a food source can be mostly eliminated in your shower substrate. Materials such as cement backer boards are not viable for mold to feed. However, any soil or contaminants on these backer boards may be enough to start mold growing.

While some of this may exist, it will never cause enough of a problem with mold as long as your substrate’s moisture is properly channeled.

It all goes back to the water, doesn’t it? Mold is like a plant as long as moisture is present. Dehydrate it, and it will die.

A fully waterproof 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 an important factor in controlling mold growth in your shower installation.

Correctly Waterproofed Shower

A shower can be fully waterproof and still have standing water that never recycles. A good example is when a shower liner is placed flat on the substrate without a pre-slope beneath it. The water in the bottom portion of that liner lies about 1/4″ below the drain’s opening and never gets flushed into the drain and recycled.

Water that remains stagnant or unmoving can grow mold if a food source is available (soaps, shampoos, etc., are all potential food sources).

A correctly waterproofed shower flushes old water and replaces it with new every time the shower is used. If the spores are not flushed through with each use, they can remain in the shower and begin to propagate.

A correctly built, full system is required to eliminate mold growing inside a shower substrate.

A full system simply refers to a shower built that does not leak, correctly eliminates any standing water, and controls water in a way that always channels it into the drain.

The most important part of a properly constructed shower is the part you will never see. When you spend all that money on the perfect design for what your new shower will look like, be sure to spend some time on ensuring all of that will prevent mold growth in the shower.

Mas Broto

Written by: Mas Broto

Mas Broto is a small business owner with 30 years experience in the real estate industry. He is the founder and editor of, the most comprehensive free home improvement website on the planet!