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How Fast Does Mould Grow On Building Materials?

Under experimental conditions moulds are found to cover artificially inoculated building materials in 4-10 days. For example, fast growing strains of Stachybotrys chartarum produce visible mould growth on new water-damaged gypsum boards in 5 days. Slow growing strains of Stachybotrys take 14 days to completely cover the test materials. These observations suggest that visible mould growth could appear within 1-3 weeks after water damage. Under natural conditions mould growth is influenced by a number of factors.

Key factors that determine how fast mould grows

  1. Type of mould: All moulds don’t grow at the same rate. Some moulds grow faster than others. For example, under the same conditions of growth, Ulocladium would grow faster than Stachybotrys.
  2. Temperature: Moulds grow faster at or closer to their optimal temperature for growth. For most indoor moulds the optimal temperature is around 25 °C. However, mould can still grow at temperatures as low as -7 °C. Some species of Cladosporium and Penicillium are capable of growing on wood at -5 °C although spore germination requires at least 0 °C. At low temperatures mould growth is very slow.
  3. Water activity: Growth rate of mould increases with increasing water activity. Most indoor moulds have their optimal water activity at 0.96-0.98. Lowering the water activity of the material lowers the growth rate significantly. However, a few species such as some species of Aspergillus, Penicillium, Eurotium and Wallemia are able to grow at lower water activities. Germination of spores requires slightly higher water activity than the minimum required for growth.

    4. White wood-rotting fungus

  4. Age of the spores: Older spores require longer time to germinate than relatively younger spores.
  5. The spore load: If a building is full of settled viable spores, mould would cover a wider area in a shorter time, than, if there were a few settled spores.
  6. Composition of the building material: Most building materials derived from plants are highly susceptible to mould attack. For instance, wallpaper allow fast growth for cellulolytic moulds such as Chaetomium and Stachybotrys.
    • pH of the material: pH of the material strongly influences the rate of mould growth, sporulation and metabolite production. Some moulds such as Aspergillus fumigatus grow best in the pH range from 4-7 and less well at acidic and basic extremes.
    • Nutrient availability in the material: Growth could be unrestricted if all nutrients are in excess but restricted when not all nutrients are in excess.
    • Presence of antimicrobial compounds in building materials: Some building materials contain antimicrobial compounds. These compounds slow down mould growth.

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  7. Competition with other micro-organisms: In a moisture damaged environment, there is a great diversity of microorganism. These microorganisms (including bacteria) compete for nutrients and also produce by-products that may inhibit the growth of other microorganisms. Fast growing moulds tend to over-grow slow growers.

    8. Picture of black mold in basement

Conclusion

Since there are many factors that influence mould growth in buildings, it is hard to say when mould growth started. However, if we know where and when the moisture problem started, we could speculate how long the mould growth has been there.

References

  1. Nielsen, K. F. (2002). Mould growth on building materials. Secondary metabolites, mycotoxins, and biomarkers. Ph.D. Thesis. BioCentrum-DTU, Technical University of Denmark.
  2. Nielsen, K. F., Holm, G., Uttrup, L. P & Nielsen, P. A. (2004). Mould growth on building materials under low water activities. Influence of humidity and temperature on fungal growth and secondary metabolism. International Biodeterioration & Biodegredation, 54(4) 325-336

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For more information on mould growth, please visit http://www.moldbacteria.com/ or call 905-290-101.

Types Of Mold

Many people often ask what are the types of mold commonly found indoors. Generally the prevailing conditions determine the types of mold prevalent in a given environment. A highly humid environment is likely to be dominated by those molds that require a lot of water such Aspergillus fumigatus, Chaetomium globosum, Stachybotrys chartarum, Ulocladium chartarum, Fusarium solani, Trichoderma sp, while a relatively dry environment may be dominated by those molds that require less moisture to grow such as Aspergillus versicolor, Eurotium spp, and Wallemia sebi. For a more detailed discussion on the types of mold commonly found indoors and their hazard classes, visit the website http://www.mouldfacts.ca/mouldtypes.html.

If you have a question concerning indoor mold or bacteria, give us a call at (905)290-9101.

Black Mold: How Do You Know If It Is Toxic?

Black mold is generally thought by the general public to be toxigenic. But what is black mold? There are a number of molds that grow indoors and they appear black. Some of these are not even known to produce any significant amounts of toxins. Stachybotrys chartarum, which is incorrectly referred to as black mold is known to produce toxins. However, even the toxigenic molds do not produce toxins all the time. Several factors including substrate composition, water activity, pH and temperature influence production of mycotoxins.

It is difficult to know whether a toxigenic mold has produced toxins or not unless the material on which the mold is growing is tested for mycotoxins.

If you are a home owner worried about black mold in your house visit this web page Mold Testing Kits For Homeowners And Property Managers.

My Mould Test Results Said Phoma: Is Phoma dangerous?

This is one of the questions we received recently from one of our web visitors. Phoma is one of the moulds that may be found in water damaged buildings. Other common fungi in water damaged buildings include Chaetomium globosum, Stachybotrys chartarum, Ulocladium chartarum, Trichoderma spp such as Trichoderma harzianum, Aureobasidium pullulans, and the yeast fungus Rhodotorula spp.

In nature, Phoma is widespread in soil and a wide range of plants and plant materials. It is one of the most important plant disease causing agents. In indoor environment, Phoma is common on wet/damp paints, wood, wall papers, window frames, and caulking especially in bathrooms. Species of Phoma are also commonly isolated from house dust. The common species in indoor environment are Phoma glomerata and Phoma macrostoma.

Phoma species are mainly contaminants, though may rarely cause infections in humans particularly to individuals with weak immune system. They are not known to pose an inhalation hazard to humans. However, any mould growing in human occupied environment should be treated as potentially hazardous.

Do you have a mould question? Call us at (905)290-9101 now!

Memnoniella echinata: how different is it from Stachybotrys chartarum?

Memnoniella echinata is an indoor mould very similar to Stachybotrys chartarum. The only obvious difference between the two moulds is that Memnoniella echinata produces spores in chains while Stachybotrys chartarum produces its spores in a mass. Memnoniella echinata was previously named Stachybotrys echinata.

Memnoniella echinata has a world-wide distribution and is mainly isolated from soil. Similar to Stachybotrys, it is isolated from cellulose containing materials such as paper, wallpaper, textiles and dead plant material. Sometimes both Memnoniella echinata and Stachybotrys chartarum occur on the same water damaged building material.

Memnoniella echinata produces toxic metabolites similar to those of Stachybotrys chartarum.

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