How Much Mould Is Too Much? Insights from Statistical Analysis of Water-Damaged Materials. LCS Laboratory has analysed hundreds of construction material samples from water-damaged buildings to identify typical and elevated mould growth levels. Our statistical approach provides clear benchmarks for interpreting mould contamination results.
Sample Collection and Analysis Overview
Samples were submitted by the general public, contractors, safety consultants, and insurance assessors, primarily from Southwestern Ontario. While the specific origins of the materials remain unknown, most samples likely came from water-damaged or mould-contaminated buildings.
To assess surface contamination, we used Phase Contrast Microscopy or Staining Microscopy at 400x magnification. Mould spore concentrations were measured in spores per mm² (sp/mm²), and the most common types of mould were identified, including:
- Alternaria
- Ascospores
- Aspergillus/Penicillium-like
- Basidiospores
- Chaetomium
- Cladosporium
- Curvularia
- Drechslera/Bipolaris-like
- Smuts/Myxomycetes/Periconia
- Stachybotrys/Memnoniella
- Ulocladium
- Hyphal Fragments
- Miscellaneous/Unidentifiable Spores
Key Findings on Mould Contamination
Our analysis revealed the following:
- 95% of samples contained detectable mould.
- Spore concentrations ranged from 3 sp/mm² to 300,000 sp/mm², with a median value of 100 sp/mm².
- Concentration distribution follows a log-normal pattern with these thresholds:
- <10 sp/mm²: Represents the cleanest 10% of construction materials.
- 100 sp/mm²: Median concentration; 50% of samples fall below this level.
- 1000 sp/mm²: 75% of samples fall below this concentration.
- >1000 sp/mm²: Indicates the top 25% of most contaminated materials.
These benchmarks provide a quantitative framework for interpreting mould assessment results, transforming qualitative microbiological observations into actionable data.
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at 5:03 pm
Meanwhile …. ASTM requires reporting in fs/cm2 not. sp/mm2
In built houses we find most building products that have not been water damaged have a fungal structure concentration of <500fs/cm2
at 10:31 am
Hi Joseph, thank you for letting me know. Which ASTM method are you using? 500 fs/cm2 sounds like a lot of mold. At 1000 fs/cm2 you can see mold stains with the naked eye.