The last thing that you want to deal with when buying, selling or living in a house is mold, especially in the visible areas like the bathroom. 

As a green contractor, our clients expect us to build in such a way so mold never appears, however some houses already have a mold problem before we even start the project.

Not only are our clients concerned about mold, members on home improvement forums such as have the same question:  “How do I kill the mold in my bathroom?” 

Unfortunately, the “knee jerk” response that most people offer as a suggestion is to try to kill the mold with bleach.  This common perception of dealing with mold can cause it to spread and also does not deal with the cause of the problem.

What is mold and why is mold growing on the walls and other surfaces of the bathroom in the first place?  Mold is a fungus and is nature’s way of breaking organic matter down so new life can emerge.

Mold grows on the surfaces of the bathroom only if you have several conditions occurring at the same time.  Let’s explore the causes of mold growth, then discuss some of the solutions for dealing with current mold growth and ways to prevent mold from growing in the first place.

Mold likes to eat

The first thing you need is a food source and most bathrooms have many potential food sources for mold. In showers and bathtub surrounds, you might see mold and/or mildew growing in the grout lines or in the corners where the moisture builds up. The mold is not eating the grout itself; it is eating deposits of organic material that is coming off of us when we shower.  When you rinse, the water splashes on the walls and the grout collects some of the dirt and organic materials that you have just washed off your body.

Mold also likes to eat the materials that are used to construct the bathroom. Most wall coverings in the US are now some sort of drywall. The newest building codes require that they come with asphalt in the outer layer which would inhibit mold growth, however if you have an older home or your contractor installed the wrong type you could have an ongoing mold problem.  

The outer layer of typical drywall is usually some sort of paper material. This paper is an excellent food source for mold and when introduced to a moist climate such as a bathroom, it can start to mold. We have seen houses where they accidentally installed the incorrect type of sheetrock near the shower and it starts to mold within a few months of exposure to the steam from the shower.

Solution: Starve the mold

Clean your tile more often so the mold does not have a chance to start eating the residue. Prevention allows you to avoid harmful chemicals that are necessary to kill the mold. If you only clean the shower once a year, you will have to wear safety goggle and a respirator and a harsh chemical. However, if you use a safe cleaner approved by organizations like GreenSeal and clean more frequently, you will be able to prevent mold and avoid harmful chemicals that can pollute your indoor air.

When constructing the bathroom, you should also use products that are mold resistant (also known as "inorganic"). One of the products that our company uses on both basements and bathrooms is a type of drywall called “paperless” drywall. Instead of using paper to hold together the drywall, materials such as fiberglass are used instead. Georgia Pacific started promoting their DensArmor plus line several years ago as an excellent alternative to standard drywall in damp locations such as bathrooms, basements and garages. By using this product, we can sleep at night knowing that our clients are not going to have a mold problem that can potential make them sick and open us up to liability lawsuits.

Mold likes moisture

Like us, mold cannot live on food alone; it also needs a water source. When you take a shower or a hot bath the steam collects on the tile, on the walls and also on the ceiling. The tiles start to grow mold because of the organic residue and the moisture. You could have a dirty shower and no moisture and the mold would not grow.

Even if you install the correct type of drywall or plaster, you can still have a mold problem on the ceiling or walls of the bathroom if the insulation is not installed correctly. In the winter months, the moist air from the shower can condense on the walls or ceiling if there is inadequate or missing insulation.

Solution: Keep your bathroom dry

The best way to prevent moisture build up is to install a bath fan. A typical bath fan alone is not going to suffice it you took a 30 minute long shower and the bathroom is full of steam. You leave the bath fan running for at least 15 minutes after you exit the shower. A timer switch is a great way to make sure you leave the bath fan on and have it shut off in order to save energy.  Manufacturers such as Panasonic have models that have a sensor and automatically come on when you enter the room and can be set to run for a short period after you leave so you don’t have to worry about using the switch or the timer switch.

If you have mold growth on either the drywall or paint, then covering up the mold is not the solution. In many cases the mold has taken a foothold in the drywall or ceiling tiles and will need to be removed and replaced. Using a professional mold remediation company is recommended since they know how to properly handle the contaminated material without spreading it to other parts of your home.

This article by Matt Hoots was reprinted with permission. It originally appeared here on

See also:

How to prevent mold

How to deal with mold
Find out how to clean and kill mold, and why it grows in your bathroom. The last thing that you want to deal with when buying, selling or living in a house is m