What Makes Mold Grow in New Jersey?

Folks often ask me what mold needs to grow indoors.  The answer is pretty simple because it involves only three things.  Just like most creatures, mold needs food, moisture and suitable temperatures.  Inside a home or office, the moderate temperatures are usually a given, so we are down to two.  The three main food groups that mold seems to enjoy are carpet, drywall and fiberglass insulation.  This is not a complete list, since mold will colonize on a lot of other materials, such as vinyl, wood, paint and leather.  The three main food groups are so common, however, that they account for the vast majority of mold problems.

Carpet is usually made from synthetic petroleum hydrocarbons that mold can colonize and drywall is coated with paper (pre-digested cellulose) that is preferred by many molds.  So it is pretty obvious how they have become foods.  But what about fiberglass?  Nobody eats glass.  That is true, but it is also true that the fiberglass does not form itself into a batt by magic.  There is a coating of adhesive resin that forms the batt during the extrusion process.  The resin on the fiberglass is the food.

If these materials stay dry, of course, they will not grow mold.  Moisture is the limiting factor in mold growth.  If the water activity (more or less the humidity level in a material) remains below 0.60 (60% RH), mold will simply not grow.  When water activity increases above ~0.65, the more dry tolerant (xerophilic) mold spores can germinate.  The higher the water activity, the greater number and types of mold can germinate.  When water activity gets above 0.90, which is approaching saturation, some of the most hydrophilic molds can germinate, including Stachybotrys, Fusarium and Aspergillus fumigatus.  Please note that we are still not talking about liquid water, just ample and chronic humidity.

So, to avoid mold contamination in New Jersey, you either need to control the water or eliminate the food.  An example of eliminating food is an unfinished basement with very limited stored materials.  Materials such as metal, plastic and glass are quite resistant to mold growth, so they can usually tolerate a damp basement.  Avoid storing clothing, vinyl, paper, cardboard, clothing and synthetic fabrics and you may be able to avoid mold growth even if moisture is present.

On the other hand, if the basement is finished or you have to store numerous materials, you must control the moisture.  This is a bigger challenge and I will discuss this more fully in my next blog.

Thank you for your attention.

David M. Kichula, CIH

Mold Contamination and Control in New Jersey