How to distinguish mold growth from other discolorations

How do we tell if it is mold growth?

• Are mold growth conditions present?
  For mold growth to occur there should be a nutrient source, moisture and suitable temperature. So, the first step would be to determine if the material being investigated for mold growth is biodegradable and its moisture content. In indoor environment, the temperature is always within the range required by environmental molds. Events that would be indicative of mold growth include water leaks, floods, high humidity and poor ventilation. Water-damaged drywall, wood materials, jute, wallpaper, and cardboard are prone to mold growth when damp. mold growth tends to follow the pattern of water condensation or leak. In cases where water damage is not obvious use of a humidity sensor and a moisture meter is recommended. Both active and inactive mold can produce volatile organic compounds which may have distinctive smell commonly described as musty or earthy. Such smells are therefore suggestive of mold growth.



• Are signs of mold growth present?
  Signs are the actual physical evidence of the occurrence of mold growth on a surface. These include:
  • mycelia or mold growth readily visible to the unaided eye as blue green, bluish, yellowish, greyish, black, white or other shades of these colours. With some molds, the observed colour is actually the colour of the spores. Colour together with texture would more or less confirm mold growth. Although it is possible to have one dominant mold, often different groups of molds grow together giving a variegated surface appearance.
  • discoloration or spotting on surfaces. As the mold grows on the material it produces enzymes for breaking down the material for easy absorption. Some molds also produce pigmented compounds that stain the surface on which the mold is growing. Irregular stains may be an indication of mold growth. Aureobasidium pullulans, Sclerophoma pithyophila, Cladosporium spp may cause black or black-blue stains on wood. The fruit-bodies and possibly dark coloured hyphae of the molds may be present.
  • water stains. Water stains are an indication of water problem and hence the possibility of mold growth.
  • damage to surfaces
  • Peeling or curling of vinyl floors, wallpaper or paint. mold (and other microorganisms) will cause structural damage to the material it is growing on. Damage may not be obvious depending on the material and the length of time the material has been infested by the mold.
  
  
  
• How to Confirm mold growth
  In some cases mold growth is obvious and may not require further confirmation. To confirm whether those coloured spots, patches or stains are mold growth or not, a magnifying glass can help to see the mold structures and for some groups even to tell the genus. On the picture below one can easily identify Stachybotrys. An investigator should have a magnifying glass in their tool kit for mold investigation. The characteristics to look for are the:
• appearance and texture.
  molds form colonies that will most often appear as fluffy, velvety or hairy spots or patches of various colours. This is easily observed with species of Penicillium, Aspergillus, and Cladosporium growing on surfaces of plaster, wall paper, paint, damp wood, carpets and other floor coverings. Actively growing mold in the early stages of growth has hair-like extensively branching filaments (hyphae), which develop a more hairy appearance as the mold matures. This can easily be seen under a magnifying glass or a portable handheld microscope. Actively growing mold may be soft, slimy, and damp and may smear when touched. Inactive or dead mold is dry, appears powdery and rubs off the surface easily subsequently becoming airborne. If one presses a sticky tape on the suspicious surface, mold should easily stick to the tape unless the surface is wet.
• fruiting structures. Fruiting structures not only confirms that the spots are mold but would also help the investigator to know which taxonomic group the dominant mold belong to.

mold and efflorescence

To read the February Issue of this Newsletter, click February Newsletter.

References

Gravesen S, Nielsen PA, Iversen R, Nielsen KF. (1999). Microfungal Contamination of Damp Buildings--Examples of Risk Constructions and Risk Materials. Environmental Health Perspectives, Supplements Volume 107, Suppl 3:505-8.

Sedlbauer, K., (2002): Prediction of mold fungus formation on the surface of and inside building components. Doctoral Dissertation, Fraunhofer Institute for Building Physics.

ABOUT THE AUTHOR:

Dr. Jackson Kung’u is a Microbiologist who has specialised in the field of mycology (the study of molds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analysed thousands of mold samples from across Canada and is currently the Principal Microbiologist for Mold & Bacteria Consulting Laboratories (MBL) Inc. MBL provides laboratory mold and bacteria testing and identification services to environmental consultants, indoor air quality professionals, institutions and homeowners across Canada. Get more information about indoor mold and bacteria at http://www.moldbacteria.com.