Myths about Mould
1. Mould can only grow where it is wet
This is not true. Mould initially needs moisture to start growing. The substrate can then completely dry out but the mould will still grow because it takes moisture out of the ambient air. The ambient air would need to have less than 4% relative humidity (which can only be reached artificially by using a desiccant) for the mould to die off.
2. Drying the substrate makes the mould go away
The only solution to reducing and/or eliminating the mould is to fix the source of moisture (leaking pipe, shower recess, etc.), dry the substrate and then physically agitate the surface using a microfibre cloth and a mould cleaning solution (we use 80% vinegar solution) to remove remaining mould. Simply drying the substrate with fan blowers and dehumidifiers may slow the progression of growth, but the mould contaminants are still present which could possibly be aerosolised in to the air causing an allergic reaction and more importantly is also able to off gas myco-toxins.
3. A mouldy musty smell is an indication of mould growth
This is only partially right as the mouldy musty smell comes from MVOCs (Microbial Volatile Organic Compounds) containing long chained alcohols, aldehydes and ketones. Often with this smell we also have secondary metabolites emitted (some of which are mycotoxins) so the mouldy musty smell itself is not toxic however it is a good indication that mycotoxin off-gassing may be occurring.
4. Bleach kills mould
We all know how to get rid of mould in our house, right? Just pour some bleach on it and it goes away, until the next time that you need to pour bleach on it again. Most chemicals have been proven to be ineffective against mould in the long run. The widespread use of chemicals fails to correct the original reason why the mould grew there in the first place. It also introduces additional air pollution into the indoor air. Specifically, bleach has a high pH which makes it ineffective to kill mould. The mould detects the bleach as a chemical attack and defends itself with exo-enzymes and a good defending membrane. The exo-enzymes makes the chlorine compounds in the bleach inert which then the fungi uses it as a food source. So when we put bleach on mould we are actually feeding it. Visually it looks like the mould is disappearing because bleach “bleaches” which means it strips the melanin compounds out of the hyphal membrane (just like the melanin in our skin when we get a sun tan). Three weeks later the fungi hyphae recovers the melanin content and the mould becomes visible again so it was actually never gone.
5. You don’t need to do any testing if you clean it up quickly
This is wrong again as you can only clean up if you know how widespread the mould is. Most of the mould is actually invisible so like with the tip of an iceberg, the black or green stuff we can see is just a very small portion of the mould. Most of the mould is hyaline (see through) and not visible to the naked eye. Failure to clean up the entire mould can result in re-growth. So before you do any cleaning it is important to find out the source and how widespread the mould contamination is, and then with a proper scope of works, protecting yourself and avoiding cross contamination, the clean-up can start.
The only proven way to deal with mould is to find the source of the moisture, fix it, dry the substrate out, physically remove the mould and then apply a mould cleaning solution, but only in the right dilutions or they will not work. The most effective cleaning solution that we have against mould so far is our favourite salad dressing - vinegar. This is claimed to be the most effective because it actually kills mould, but doesn’t introduce a new chemical pollutant into the indoor air. Vinegar is even used by some European hospitals as one of their main disinfectants.
A point of note is that only white fermented vinegar seems to work, as synthetic acetic acid does not appear to be effective. Diluted alcohol comes a close second, but there are a number of issues concerning its acquisition, storage, handling and OHS, PPE, duty of care and its effects on some surfaces that make it difficult to recommend.