Avoiding mold on a jobsite

Mold is all around us and can be an important part of life. People have found ways to use mold. For example, one of the most common antibiotics, penicillin, was developed from mold. And if you’ve ever wondered what gives blue cheese its distinctive color, it’s the mold that spreads through the cheese as it ages.

Mold can also cause concerns. Certain types of molds can create toxins that can have negative health effects, leading many to panic at the sight of green or black spots. Much of that panic is driven by poorly informed people, but for some individuals, the danger can be real.

It’s not unusual to encounter mold during construction or demolition of buildings. In addition, failure to take the right precautions during construction can create environments in which mold may thrive. Because of the potential for legal liability and health problems, it’s a good idea for construction crews to develop a basic understanding of mold and treat it with respect.

Just what is it?

Mold is a type of fungus that can be found both outdoors and indoors throughout the year. While many assume that mold is a single species, there are actually thousands of different types of mold, and fewer than 100 that are believed to create health issues when encountered indoors. Those issues can range from simple nasal congestion or eye irritation to more serious problems, deepening upon the species, the degree of someone’s allergy, and the amount of exposure. People with weakened immune systems may be at increased risk.

Most molds thrive in damp conditions. They spread by releasing millions of microscopic spores that may float through the air, travel along moisture, or even be carried by insects. The spores are what causes allergic reactions in people. Some molds also produce mycotoxins, which are toxic agents that may be harmful to humans. But just because a mold can be seen doesn’t mean there’s a hazard to people. Again, it depends on the type, the degree of exposure, and how a particular mold works with an individual’s body chemistry.

Mold and construction

Most molds require warm, humid environments and some kind of organic matter to thrive. The moisture can be caused by high humidity or exposure to water from condensation or flowing liquids. As for organic matter, materials such as wood, drywall, and ceiling tiles provide a source of sustenance for many mold species.

During construction projects, moisture tend to become an issue in several different ways. It can be caused by poor site drainage, stored building materials that become wet from rain or snow, leaking water pipes, and failure to protect the building from weather. Within 24 to 48 hours after building materials such as drywall and ceiling tiles become wet, visible mold can begin to form. And the longer those materials stay damp, the more that mold will grow. If materials with active mold growth are used in construction, the mold may continue to grow if exposed to enough humidity.

Preventing the spread

Fortunately, there are steps that can be taken to discourage the growth of mold. So-called “greenboard” is a type of drywall to which wax is added to make it more resistant to moisture. Some builders shy away from greenboard because of its slightly higher cost, but when viewed as part of the total project cost, the difference between greenboard and traditional drywall is minimal. The use of moisture barriers and capillary breaks can also limit the environment for mold.

Practical steps to keep vulnerable building materials dry can also discourage mold growth. Storing drywall and wood in a dry location that’s raised off the ground (and inspecting them upon delivery) is one such step. Another involves sealing the building envelope before beginning interior construction. Thoroughly dry any materials that may have become wet before installation. For example, wood subfloors that become wet in the rain can release moisture long after the rain has ended, and if the envelope is sealed before they dry, they may be a source of humidity.

Pay attention to outdoor drainage to ensure that stormwater drains away from the foundation, and that roof drains are large enough and properly mounted. Make sure all water lines are free of leaks and insulate pipes that could develop condensation. Check all windows, doors, vents, and other penetrations to ensure they are properly sealed and flashed.

Basic remediation

During construction, have a plan for what you’ll do if there’s a water incursion. For example, you may want to have ready access to wet-vacs, fans, and dehumidifiers to dry out building materials. It’s important to dry materials as soon as you can after they come in contact with moisture, even if that means having to open wall cavities. Inspect electrical and HVAC equipment to ensure they can be used safely.

If you see mold, don’t begin to clean it until you take care of any sources of moisture, because the presence of that moisture will continue to feed the growth of the mold. When you’re ready to begin cleaning, obtain the advice of an environmental professional. Many people reach for bleach, but the EPA and OSHA do not recommend its use. UV lights and ozone generators also tend to be ineffective. In some situations, you can encapsulate mold by using paints with high zinc levels.

What about monitoring?

Given the potential for mold-related problems, it might seem that ongoing testing and monitoring would be prudent. The problem is that scientists haven’t been able to agree on what levels of mold are safe. There’s no PEL for mold, for example.

If you plan to test, make sure you obtain samples simultaneously from the outdoors and the area where you suspect a mold problem. Comparing the results is the best way to tell if there are substantially more spores indoors. But again, having more spores doesn’t necessarily translate to an elevated health risk. Mold surrounds us.

The best way to check for the presence of mold is generally to use your senses. Look for visual signs of mold or discoloration on building materials. A musty smell may also be a warning sign. If you think moisture may be present in building materials, you can use a meter to measure the level. And, if you believe you have a significant problem, don’t panic. Instead, bring in an environmental professional who specializes in working with mold.


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