Is It Mold or Isn’t It?

Concern about illnesses caused by certain types of mold has increased as high water tables and flooding have contributed to an ideal environment for mold growth. As people scour their homes for mold, what they find may not necessarily be mold.

"People are looking in places where they probably haven't paid too much attention in the past, like storage rooms in basements," notes NDSU Extension Service water quality specialist Bruce Seelig. "In some cases, what they’re finding are mineral deposits, not mold."

The wet, humid conditions that contribute to mold growth in basements are often the result of a high water table. If the water table comes into contact with basements that are inadequately drained or sealed, moisture will slowly seep through the foundation, Seelig explains. 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 over time, salt crystals grow and become obvious to the naked eye. These crystals can take many different forms depending on the relative amounts of sodium, calcium, magnesium, carbonate, chloride, and sulfate or other physical factors such as the relative humidity or rate of evaporation," Seelig says.

Many different types of salts exist and each has its own properties, such as solubility. Solubility of a salt is a measure of the total amount of salt that can be dissolved in a given quantity of water.

Usually chloride salts, such as table salt, are extremely soluble. Carbonate salts such as lime, on the other hand, are generally very insoluble. Calcium and magnesium carbonates are two common salts found throughout North Dakota that are relatively insoluble, Seelig says. Upon evaporation, they cause light colored powdery deposits that accumulate over relatively long periods of time. These deposits can be removed with a dilute acid solution such as vinegar but cannot be effectively removed with water alone. The white plaque that is often seen on plumbing fixtures and in water tanks or on basement walls and floors are carbonates and are quite harmless.

Sulfate salts tend to be less soluble than chlorides but more soluble than carbonates. Sulfate salts are generally the type of soluble salt found in North Dakota, Seelig says. Sodium and magnesium sulfates are soluble salts that exist in much of the geological material in North Dakota. These salts are readily dissolved and transported in groundwater. "When they are redeposited on basement walls and floors they often take on a white filamentous or moldy appearance. These deposits are easily redissolved by water," he says.

Deposits of soluble salts on basement walls and floors are harmless from a human health standpoint. 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 by forming crystals in the pores that eventually expand and physically break down the internal structure of the concrete," Seelig explains.

As one might expect, 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.

Solutions to this problem include a proper tile drainage system around the basement foundation and floor that quickly removes water from the immediate area of the basement. Also, some types of cement are more resistant to sulfate corrosion than others. Standard Portland cement (Type I), which is usually used for most structures, is the least resistant. Type II cement has some resistance and can be used where sulfate concentrations in the groundwater are 150 - 1000 parts per million. Type V cement has high resistance to sulfate corrosion and should be used where groundwater has sulfate concentration of more than 1000 parts per million.

Some areas of North Dakota have significant areas of saline or sodic soils. These areas are likely to have water tables close to the surface with high concentrations of sulfate salts. Only a field investigation will provide accurate information that can be related directly to a given building site; however, a homeowner or prospective homeowner can get a general idea about the soils in their area by consulting a county soil survey at the local Natural Resource Conservation Service (NRCS) office.

"A little extra time and money spent prior to and during the construction of a new home may save thousands of dollars down the road," Seelig says.

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Source: Bruce Seelig, (701) 231-8690, bseelig@ndsuext.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu

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