Indoor Environmental Quality: Questions and Answers
Notice the use of the phrase indoor environmental quality instead of indoor air quality (IAQ). The indoor environment is more than just the air space within a building. The Indoor Environmental Institute has described the indoor environment as “…an ecosystem that encompasses everything that impacts the indoor air and its occupants, to include influences from the outdoor environment, the structure that surrounds the air space indoors, the building contents and the occupants. It might be said that the built environment comprises ‘the conditions that surround one.’”
The intent is to focus attention on IEQ issues that relate to the cleaning, restoration and remediation industries, including health and safety; work practices that protect workers; work practices that may contribute to good or bad IEQ; building considerations that might adversely affect workers or occupants; equipment and it’s operation that might adversely affect workers or occupants; standards, guidelines and regulations; and other IEQ-related subjects that pertain to the cleaning and restoration professional.
Q: Can wet cleaning procedures such as stripping or mopping cause mold to grow in walls? What can I do to prevent this?
A: Drywall that becomes wet as a result of wet-cleaning floors can lead to mold growth (Image 1). In order for mold to grow on building materials, it needs water and a food source. The cellulose in many building materials, such as wood and the paper surface of gypsum wallboard, is a good food source. Even ceramic and other non-nutritive materials may have sufficient nutrients in a dirt or bio-film layer for mold to grow. Situations where mold grows in walls are more likely to develop as a result of stripping floors or employing other cleaning procedures that use massive amounts of water. However, it could also develop from ordinary mopping performed without attention to proper technique.
In 2002, researchers from the Institute of Occupational Health in Kuopio, Finland investigated school buildings that had liberal amounts of water applied during floor scrubbing or stripping operations occurring once or twice a year. The researchers found these buildings developed mold damage behind baseboards and in wall cavities when water was allowed to build up against walls, seep inside and then was unable to dry quickly.
The vulnerable point is generally where the wall meets the floor (Image 2). If the floor is waterproof vinyl or ceramic tile, the wall is covered with vinyl wallpaper and the juncture is protected with vinyl base molding, it is easy to assume that the assembly is essentially moisture-proof. However, this combination of materials, as they are usually installed, does not prevent water from penetrating into underlying gypsum wallboard and wall cavities.
Capillary action causes water to wick into materials through very small cracks and openings where these materials meet. Once the water has entered, the impermeable materials trap it. Water entry may also cause swelling, allowing additional openings to form.
Surface mold species like penicillium and aspergillus can colonize materials in as little as two to three days. According to the Finnish study, stachybotrys was found in some of the samples. It states, “Stachybotrys is considered a sign of serious mold problems connected with flooding or situations connected with free water.” Stachybotrys requires very wet conditions for seven to 14 days to begin colonization. If wood remains at a moisture content above 20 percent, various types of rot organisms may even cause structural weakness.
Chemical additives and antimicrobial agents are generally not effective in preventing mold from developing when repeated wettings occur. These chemicals are frequently inactivated by the presence of dirt or organic materials, and usually cease to work long before the water dissipates. According to “Bioaerosols: Assessment and Control,” a publication of the American Conference of Governmental Industrial Hygienists, “Antimicrobial agents should not be used in place of moisture control in buildings.”
There are several ways to prevent mold damage from developing as a result of wet cleaning. Ideally, during the building’s design phase, materials and construction techniques that facilitate the use of wet-cleaning processes will have been incorporated.
Prior to beginning wet cleaning, the area should be evaluated to determine if at-risk materials are present. Sealed concrete floor and wall systems are an excellent preventive construction technique. Various types of reinforced cement-type panels are a preferable to drywall for use in areas where wet cleaning is anticipated, as they do not degrade when wet. However, these panels may not prevent water from entering into the wall cavity behind them, which may still result in mold growth and/or decay of the framing materials and insulation. Make sure that base moulding or cove base is securely attached and sealed, or that ceramic tile grout is in good condition.
Unfortunately, many situations exist where the building has been constructed without consideration for moisture control. In these cases, care must be used during the cleaning process. Water use should be minimized. Mops should be wrung almost dry when used around unsealed joints. If cove base, wall cavities or other areas collect moisture, they may require rapid drying using air movers and other drying equipment to prevent mold growth. Moisture meters may be necessary to determine whether these areas have become wet.
The Finnish study concluded that, “Cleaning should not lead to the deterioration of indoor air, but it should be considered as an important factor in creating good indoor air quality.”