Flood Information


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Is It Mold?

Homeowners concerned about the health effects of exposure to mold may be looking for it in the damp conditions that high water tables and flooding create.

“However, as people scour their homes for mold, what they find may not necessarily be mold,” says Ken Hellevang, North Dakota State University Extension Service flood expert. “In some cases, what they’re finding are mineral deposits.”

The wet, humid conditions that contribute to mold growth in basements often are the result of moisture vapor coming through the concrete floor or wall because of a high water table or saturated soils. If water comes into contact with inadequately drained or sealed basements, moisture will seep through the wall and floor. The result is not only a damp environment, but mineral deposits (salts) left behind as water evaporates from basement walls and floors.

As water evaporates, salt crystals grow and become obvious. These crystals can take many forms, depending on the relative amounts of sodium, calcium, magnesium, carbonate, chloride and sulfate in them, or other physical factors such as the rate of evaporation.

Sodium and magnesium sulfates are found frequently in some areas. These salts are dissolved and transported in groundwater readily. When they’re deposited on basement walls and floors, they often appear to be a white, fluffy or moldy substance in floor or wall cracks. Water easily dissolves these deposits. Putting a few drops of water on them is one way to determine if they are salt or mold.

Calcium and magnesium carbonates also are found in some areas, but they are relatively insoluble in water. They cause light-colored, powdery deposits that accumulate during relatively long periods. These deposits can be removed with a dilute acid solution, such as vinegar, but cannot be removed effectively with water alone.

Carbonates cause the white plaque you often see on plumbing fixtures, basement walls and floors and in water tanks. If the substance does not dissolve with a few drops of water, try using a few drops of vinegar. If the substance still doesn’t dissolve, then it may be mold.

Soluble salts deposits on basement walls and floors are harmless to human health. However, groundwater with a high concentration of sulfate (more than 150 parts per million) is corrosive to concrete basements. Sulfate corrodes concrete by degrading the cementing agent and forming crystals in the pores that eventually expand and break down the concrete’s internal structure.

“As the amount of sulfate in the groundwater increases, and the longer the concrete basement is in contact with groundwater, the greater the damage from corrosion,” Hellevang says. “Solutions to this problem include a proper tile drainage system around the basement foundation and floor to quickly remove water from the basement.”

For more information, www.ag.ndsu.edu/flood or www.extension.org/Floods.

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