Episode description

Think that mould only grows on bread, or on rotting fruit or if it does get inside your home - doesn’t it just live inside your air conditioning ducts where condensation can form, or if there’s been a flood or unexpected water ingress then it might grow on damp wall linings like gyprock plasterboard or on soft furnishings like backpacks or curtains?

This week, I’m wanting to talk about mould growth in extreme habitats like stone and mineral building elements. Think it can’t happen? I didn’t? I thought the only time microbes attacked walls was on really old ones where cultural artefacts like murals in churches or in caves become damaged. This phenomenon is called biodeterioration in the literature. However, I want to share with you some results from an inspection I did where we found mould growing not just on old plaster, but behind bricks, in old mortar joins, behind and between excised bricks and when we cracked some of the bricks open, there was even mould growing inside!!!! How can this be explained? After all, bricks and other stone materials like concrete and terrazzo-type floor tiles are typically a pretty poor foodstuff for microorganisms.

In a recent elegant experiment, some scientists from Israel and Germany did an elegant experiment showing that a fungus called Nigrospora spherica was the dominant fungus with a 100% match with the fungus found growing in efflorescence degrading stone chips of terrazzo floor tiles. When the particle size of the terrazzo was <1mm, the fungus dissolved more than 70% of the powdered tile in 10 days.

Now imagine what happens to your brick work when it gets wet and you see efflorescence. That’s a sign of fungal attack. If you have rising damp, you have slow biodeterioration going on indoors. Health concerns were raised by the authors of this study about breathing in the crystalline salts by residents where terrazzo tiles are breaking up.

This type of dilapidation happens eventually in the built environment. Now I want to show you some examples of fungi growing in a water damaged building inside a wall behind thick plaster….look at the clearly visible mycelium…. What about concrete? Typical fungi to those seen in the contaminated bricks include Aspergillus fumigatus and Penicillium brevicompactum. When concrete specimens were inoculated with these typical fungi and tested for stability and examined under a scanning electron microscope…do you know what they saw and found? The fungi induced: Calcium release from the concrete. If the concrete was wet, then they saw more rapid calcium loss compared to drier concrete.

After 28-days of growth with Penicillium, the stability of the concrete showed a 1% loss.

Now, lets revisit the mould in brick examples… What do you think is going to happen to your house if there’s a fire and the whole house is saturated? How is your remediation process going to get the mould and spores and biofilms out of the bricks, inside the bricks and between the mortar joins?

Citation: Jones CL. Guidelines for the assessment of viable fungal hygiene on indoor surfaces using RODAC petri plates. J Bacteriol Mycol Open Access.
2019;7(5):116‒126. DOI: 10.15406/jbmoa.2019.07.00256

REFERENCES:

Metabolic Activity of Micromycetes Affecting Urban Concrete Constructions.  The Scientific World Journal. Volume 2018, Article ID 8360287, https://doi.org/10.1155/2018/8360287 OR https://www.hindawi.com/journals/tswj/2018/8360287/abs/

Laboratory study of fungal bioreceptivity of different fractions of composite flooring tiles showing efflorescence. Appl Microbiol Biotechnol. DOI 10.1007/s00253-014-5628-4 OR https://www.ncbi.nlm.nih.gov/pubmed/24652060

Concrete Damage in Field Conditions and Protective Sealer and Coating Systems. Coatings 7(7): June. DOI: 10.3390/coatings7070090 OR https://www.mdpi.com/2079-6412/7/7/90