Expert Witness Journal Issue 67 June/July 2026 - Flipbook - Page 119
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able to grow even when concentration of sodium
are delivered to samples. As it increases the levels of
nitrate available to the mould as a food source.
As polysaccharides are frequently found
association with gypsum in two main contexts:
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in
As additives in commercial products: Polysaccharides
such as starch ethers, cellulose ethers (like
carboxymethylcellulose or CMC), and dextrin are
widely used as additives in commercial gypsum-based
materials (plasters, mortars, wallboards). They are
added to modify the material’s properties, such as
controlling setting time, improving rheology (昀氀ow
and workability), and enhancing water retention for
speci昀椀c applications like 3D printing or plastering.
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Polysaccharide Digestion
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Stachybotrys chartarum’s ability to digest
polysaccharides is linked to its production of
cellulolytic enzymes, which break down cellulose
and other plant-derived polysaccharides. It is
the nitrate that is in short supply in the gypsum
which is delivered to the surface through
e昀툀orescence processes.
Stachybotrys chartarum can metabolize
polysaccharides in plaster and other celluloserich materials, once sodium id broken down
and nitrates are available to it to feed upon. but
this process is not directly triggered by sodium
reduction itself but as a by-product of leaching.
Instead, the fungus thrives when nitrate
cellulose and polysaccharides are available, and
competing salts or alkaline conditions are at a
positive ph., which makes the substrate more
accessible for enzymatic breakdown
To block or immobilize nitrate in gypsum, you
typically need to use additives or chemical
binders that either trap nitrate ions or reduce their
mobility. Common approaches include aluminium
or iron salts, pozzolanic additives (like 昀氀y ash or
metakaolin), and specialized admixtures that bind
anions. These are used in gypsum board or plaster
formulations to control unwanted nitrate migration
and e昀툀orescence. Saturation of buildings releases
the nitrate and reduces the sodium to a point where
the Stachybotrys Chartarum can colonise.
Plaster and gypsum often contain sodium
salts (e.g., sodium sulfate).
EXPERT WITNESS JOURNAL
Forensic Building Pathology: In plaster
systems, sodium reduction (e.g., e昀툀orescence
leaching) can inadvertently increase fungal
colonization risk by exposing polysaccharides
and nitrates making available it food source.
Hypothesis of how to stop Stachybotrys
Chartarum from colonising buildings
Role of Sodium in Plaster:
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S.
chartarum
secretes
hydrolytic
enzymes that degrade cellulose and
other polysaccharides into glucose and
oligosaccharides.
These sugars are then metabolized via
glycolysis and other fungal metabolic
pathways,
supporting
growth
and
sporulation.
This explains why the fungus is most
often found in water-damaged plaster
and drywall as moisture activates enzyme
activity reduces salt crystallization barriers
and releases nitrates.
Summary: Stachybotrys chartarum does not
“eat sodium,” but when sodium salts are reduced
in plaster, the fungus gains easier access to
polysaccharides (cellulose, starch), which it actively
metabolizes for growth
Nutrient Source:
Stachybotrys chartarum is a cellulosedegrading fungus. It colonizes gypsum-based
plaster, drywall, wallpaper, and other building
materials because these contain polysaccharides
(cellulose, hemicellulose, starch) which serve
as its primary carbon source once sodium is
broken down and nitrate is available through
leachiung.
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Mechanism of Polysaccharide Breakdown:
ɿ
In natural microbial environments: In nature,
microbial communities can colonize gypsum
outcrops. The organic matter embedded within
these natural gypsum deposits has been shown to
contain polysaccharides, which are components
of microbial extracellular polymeric substances
(EPS). Certain bacteria isolated from gypsum
dunes are even known to synthesize extracellular
polysaccharide
High sodium concentrations can create
osmotic stress or alkaline conditions that
allow for fungal growth.
When sodium levels are reduced
(through leaching, chemical reaction, or
environmental changes), the substrate
becomes less hostile, allowing fungal
enzymes (like cellulases and hemicellulases)
to act more e昀케ciently on polysaccharides.
Once nitrates are releases due to leaching.
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Source: Gypsum (CaSO4·2H2O) can contain
impurities such as sodium nitrate or potassium
nitrate, especially in recycled or industrial
gypsum.
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Problem: Nitrate salts are highly soluble. They
migrate to surfaces, causing e昀툀orescence,
staining, and increased moisture retention,
which in turn promotes mould colonization.
JUNE 2026
