LCS Laboratory has examined thousands of construction‑material samples collected from buildings with suspected water damage. By analysing these samples and applying a statistical approach, we established practical benchmarks that help inspectors interpret whether mould growth on a surface is typical, elevated, or severe.
Where the Data Comes From
Samples were submitted by homeowners, restoration contractors, indoor‑air consultants, and insurance assessors across Canada. While the exact building histories were not always provided, most materials showed signs consistent with moisture exposure or visible mould.
To quantify surface contamination, each sample was examined under Phase Contrast Microscopy or staining microscopy at 400× magnification. Results were reported in fungal structures per mm² (fs/mm²), and the dominant spore types were identified. Common findings included:
- Alternaria
- Ascospores
- Aspergillus/Penicillium‑like
- Basidiospores
- Chaetomium
- Cladosporium
- Curvularia
- Drechslera/Bipolaris‑like
- Smuts / Myxomycetes / Periconia
- Stachybotrys / Memnoniella
- Ulocladium
- Hyphal fragments
- Miscellaneous or unidentifiable spores
This combination of spore counts and species information provides a clearer picture of the contamination level and the likely moisture conditions that produced it.
Interpreting Mould Growth on Building Materials
After reviewing results from several hundred samples collected between 2020 and 2023, four concentration ranges emerged as reliable indicators of contamination severity:
- < 15 fs/mm² — Negligible growth
Found in roughly one‑quarter of the cleanest materials. Typical of dry, well‑maintained surfaces. - 15–100 fs/mm² — Moderate growth
Below the overall median. Often associated with early or limited moisture exposure. - 100–700 fs/mm² — Active growth
Above the median. Indicates sustained moisture and conditions favourable for mould proliferation. - > 700 fs/mm² — Aggressive growth
Represents the top 25% of the most contaminated samples. Common in materials with prolonged water damage or chronic leaks.
These ranges convert what is often a subjective visual assessment into quantitative, defensible data. Inspectors can use them to support remediation decisions, document insurance claims, or explain findings to clients.
How These Benchmarks Help Field Professionals
For home inspectors, mould consultants, and HSE specialists, numerical thresholds offer several advantages:
- A consistent basis for determining whether mould is incidental or significant
- Support for recommending remediation, material removal, or further investigation
- Clear documentation for insurers, contractors, and property owners
- A way to compare multiple samples from the same building or across projects
This approach reduces ambiguity and strengthens the technical foundation of mould assessments.
Support From LCS Laboratory
LCS Laboratory provides accredited testing for mould, air quality, and building‑material contamination. Our team can help you select the right sampling method, interpret results, and manage testing costs effectively.
To request a quote or obtain sampling instructions, contact LCS Laboratory through our Contact Us page.
2 Responses
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
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.