It is a fact that mold is everywhere; it is inside, outside, in the air that we breathe, on our clothes, and on our bodies. Mold can grow in most habitable climates around the world. We as humans can do little to totally eliminate mold in the world, but we actually don't want to.

Mold and other various forms of fungi play a critical role in the balance of nature. If we eliminate mold completely from the world, we would begin to be overrun by dead organic matter. Fallen leaves, dead wood and other organic materials will continue to pile up in the environment. Mold is important in nature to provide the decay of these organic materials, and allowing this decaying matter to enter back into the environment and provide a food source for future growth of vegetation. We also use different molds for other human good. One species of the mold penicilium (Penicilium Notatum) is used to manufacture penicillin. There are other molds which are important in the manufacturing of wine, bread, cheeses and other foods.

It is unfortunate, but true, that a vast majority of the population does not see the good that mold performs. Most of us have seen mold in our home, work or hotels. We see mold, often in showers or other wet areas, and we do everything we can to get rid of it. Unfortunately, there are some battles that cannot be won outright. The good news is that mold can be controlled with some effort.

The first step to controlling mold is to know and understand what it is and what it needs to flourish and grow.

What is mold?

Simply stated, mold is a living organism (part of the family of fungus) that can grow on virtually any organic substance. Other members of the fungus family are mushrooms, yeast and mildew. Many members of the plant world have chlorophyll to help them create their own food, but fungi lack chlorophyll and therefore rely on getting nourishment from other organic food sources. There are approximately 100,000 known types of mold, and some of these are considered toxic. Toxic molds produce mycotoxins or aflatoxins that may cause health problems in certain humans. Members of the fungi family do not digest food internally. Rather, they excrete enzymes onto the food source and break it down into smaller components that they can readily use as nutrients. Whatever is left behind can be used in nature's recycling process. Once mold starts growing and flourishing, it can multiply exponentially.

Why do I have mold in my house? This is easy. Mold requires four factors in order to thrive and grow: an organic food source, oxygen, warm temperature and moisture. The ability to control any one of these factors gives you the ability to control mold. Let us look at each factor one by one.

Food source

Mold requires an organic food source to thrive. Paper, wood, dust, organic adhesives and many other organic-based materials are viewed as “mold food.” There are very few, if any, structures that have absolutely no organic materials present in the construction. There are millions of homes built with wood frame construction, and in the right conditions, the wood used to construct the house can be food for mold. It would be practically impossible to remove organic building materials from most new construction and totally impossible to remove organic construction materials from old structures.


Unless you have a type of self-contained breathing apparatus, then eliminating oxygen from the environment is out of the question.


Humans and mold both thrive in similar temperature ranges. Temperatures from 65 degrees F (18 degrees C) to 90 degrees F (32 degrees C) are optimal for humans and mold alike. Since we would be uncomfortable living in temperatures outside of this range, then temperature control would not be an option for mold control.


Mold requires moisture to grow and flourish. The moisture can be in any form, including direct water contact, high humidity or water-saturated organic material. Mold can grow even if there is no visible presence of moisture and the relative humidity is 55% or higher. Moisture would be the easiest of the four factors to control.

If moisture is coming from an unknown source, then finding and fixing the problem are critical to helping control mold. There are many humidity-causing conditions that can facilitate mold growth, including poor construction detailing, lack of proper drainage, leaking plumbing, poor landscaping, poorly maintained HVAC systems and inadequate venting.

Keeping in mind that we live indoors in suitable temperatures, and we are breathing oxygen, means that mold can grow anywhere that there is “food” and moisture. These areas include under bathtubs or showers, behind vinyl wallpaper, in wall cavities, underneath flooring, in HVAC systems or any other damp area that contains “mold food.” Mold does not grow well on certain types of material that it does not consider “food.” These materials include plastic, vinyl, epoxies, concrete (or other Portland cement products), ceramic tile and natural stone. This is great news for the stone and tile industry because these are materials that can be used in the fight against mold.

The first argument against this line of thinking is, obviously, “I have seen mold growing on the grout in my bathroom. Isn't grout made from either Portland cement or epoxy?” Yes, most grout materials are Portland cement-based, and we see more and more epoxy grout being used in showers and tub surrounds. So then why is mold growing there? If you look at what mold requires to grow and then look at what is present in a bathroom, you can see why this is the ideal environment for problems. Mold is not using the grout as a food source; it is using materials that are on the surface of the grout as the food source. These materials include soap, soap scum, shampoo, dead skin and hair - to name a few. With a food source on the grout, it would appear that the mold is actually growing on the grout itself. Portland cement products have capillaries - or microscopic holes - in them, and the mold spores are small enough to get into these holes. It can be very difficult to completely remove the “mold stain” from these areas.

Another problem when installing stone in showers and tub surrounds is the popularity among installers of organic adhesives - or mastics. These adhesives are a virtual cornucopia for mold. Since no stone or tile installation is waterproof, this means that moisture will be able to get to the adhesive. If there is no waterproofing membrane present, then the moisture can get into the substrate and beyond; thus causing unseen damage for extended periods. Once the system behind the stone gets wet, the feast begins and mold runs amok for years before the problem becomes apparent.

What can be done to help control mold?

As previously stated, the easiest way to control mold is to control moisture. So the following are easy steps to help control moisture:

  • Look for condensation and wet spots. If you see wet areas, fix the cause of the moisture and dry the affected areas within 48 hours.

  • Fix leaky plumbing and any leaks in the building envelope.

  • Prevent moisture condensation by increasing the surface temperature, properly insulating exterior walls and increasing ventilation.

  • Replace HVAC filters regularly. HVAC systems are a good way for mold to move around a structure. HVAC duct work is not a food source, but it almost always contains dust, other food sources and moisture.

  • Keep HVAC drip pans clean and flowing properly.

  • Maintain an indoor relative humidity of 55% or less by using a dehumidifier. Monitor humidity levels.

  • Do not let foundations stay wet. Make sure that the ground around the house is properly pitched away from the structure. If foundation moisture is a constant problem, it may be necessary to install foundation drainage (French drains, curtain drains, etc . . . ) to more effectively evacuate water.

  • Maintain an air space of at least 1 foot between furniture and an exterior wall to allow for air flow and provide the ability to see damp areas.

  • Make sure that attic space is properly vented because moisture vapor travels up and can collect in attic space.

  • Control moisture in bathrooms.

These are some easy steps to help control mold in the bathroom environment.

  • After every shower or bath, dry the tub or shower area with a towel. This will quickly remove most of the excess water from the area. Don't leave the wet towel lying around for more than 48 hours, because towels are usually organic based (mold food).

  • Allow the bathroom vent fan to run while showering and for about 30 minutes afterwards. This takes a great deal of the moisture vapor out of the air and sends it somewhere else (hopefully outside). Make sure that the fan vents to the outside of the structure and not into the attic or another room in the house.

  • Do not install carpet in a bathroom. This environment is perfect for a stone installation.

  • Establish and maintain a suitable cleaning regimen. Keep in mind that soap scum, shampoo, and other organic materials can be on the surface and remain unseen. Use a neutral pH soap and rinse well with clean water. Then dry with a towel while keeping the vent fan on.

  • Avoid using organic setting adhesives in a wet environment. These adhesives include mastics and wallpaper glue.

Stone solutions for mold

A couple of years ago, research began addressing the fact that mold was becoming a major factor in the building industry and looked for ways to help inhibit the growth of mold in stone and tile installations. By introducing an anti-microbial additive (biocide) into certain products, it was determined that a stone or tile installation could help inhibit the growth of mold into the system.

Biocides are proprietary agents that either kill mold outright or inhibit the ability of the mold to reproduce. The biocide is added into the stone or tile installation product during production and is fully incorporated during the mixing process. Once incorporated, the biocide additive migrates to the surface to maintain a constant equilibrium within the product structure. The anti-microbial protection will continue for the life of the product into which it has been added. When mold comes in contact with an anti-microbial protected surface, the biocide is absorbed into or is diffused through the mold cell membrane, where it either inhibits reproduction or kills the mold outright.

Keep in mind that the use of products that incorporate the biocide technology does not eliminate the need to maintain a suitable cleaning regimen. Anti-microbial agents will not inhibit the growth of mold located on the surface of the tile or grout if a food source and moisture are present.

The first line of defense against mold-related problems is knowledge. The more that the architect, general contractor, stone contractor and end user know about the mold problem, the easier it is to control the problem.