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Most are familiar with Stachybotrys, the “toxic black mold”, which is common to water damaged gypsum wallboard. Stachybotrys mold requires high moisture availability, known as water activity, to develop. Optimal mold growth is achieved at .98 water activity, which is a lot of moisture. Black moldy patches, powerful moldy odor, and lots of water, usually make this mold hard to miss. The real danger of hidden mold is the ability for a small mold problem to develop into a large and expensive one before being noticed. Wallpaper can help to make that possible.

Wallpaper is more than a decorative wall covering. In fact, any large surfaced item or treatment added to a wall, such as bookshelves, paint or wallpaper, can alter the vapor and thermal performance of a wall. This knowledge is particularly important for the perimeter walls of the home, but should be a consideration for some interior walls, as well. A well designed wall will slow the progression of moisture through the wall and yet allow it to pass through before trapping moisture and allowing conditions that will permit mold or water damage to develop. Many wallpaper types impede moisture migration at the most crucial location, the coldest surface of the wall. The obstacle also makes possible a higher water activity in the underlying wallboard that leads to hidden mold growth.

Long before the distinctive odors and black splotches of Stachybotrys manifest to any notable degree, other more insidious molds may develop. Some mold thrives in climates with very little water activity. Such mold growth can be extensive before obvious external clues develop. However, there may be clues. Look for very faint red, yellow, blue or purple stains that might be mistaken for a fruit juice stain. The mold stain can be small and circular, large and streaking, or a combination. Such observations will require further scrutiny to determine if there is mold growth under the wallpaper. Look closely for these stains to be associated with areas where the wallpaper has lost adhesion. Mold needs adequate nutrition to survive. Wallpaper adhesive can make excellent mold food and bubbles may appear where the wallpaper no longer sticks. If you see bubbles, but not stains, a more invasive approach is needed. With your wallpaper repair kit handy, use a razor blade to cut the wallpaper and inspect for underlying mold growth. Anything other than clean wallboard is suspicious. Mold can be many colors and even colorless.

Once you have discovered hidden mold, it’s time to determine to what extent the mold has developed. Determining the moisture source is paramount in estimating the size of the damaged area. You may find that the damage is small and limited to an area around a leaking window, air conditioning unit or associated with a vent blowing cold air directly onto the area. Or, something more serious may have developed.

About The Author:
Thomas Ray promotes better indoor living through his expert Environmental View of indoor environments. While helping occupants improve their indoor air quality, he shares years of mold inspection experience and investigative secrets with clients and readers. More can be learned from ENView at http://www.enviewonline.com.

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