Expert Witness Journal Issue 67 June/July 2026 - Flipbook - Page 122
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They act as water-retaining agents, slowing
evaporation and improving plasticity during
application. They help control the setting time
and improve the plaster’s spreadability. They
can also enhance bond strength between plaster
and substrate.
Or we could add a breathable, hostile topcoat as
a back-up (mineral/alkaline or acidic coating or
approved dry-昀椀lm antifungal agents, and if nitrate/
chloride salts are present treat them as a moisture
ampli昀椀er: stop the moisture path.
In short: minimise or substitute the food, stop it
reaching the surface, and stop salts keeping the
surface damp.
Problems in Damp Environments
The polysaccharides form a nutrient source for the
Stachybotrys Chartarum, Carbohydrates provide
carbon that the Stachybotrys chartarum can
metabolize. This makes available not only calcium
but also carbohydrates, nitrates and cellulose all of
which Stachybotrys Chartarum consumes.
Summary
It is thought that stachybotrys chartarum is not
moisture dependent but is reliant on the moisture
breaking down the sodium making available the
nitrate and carbohydrates that In dry conditions,
remain inert. In damp conditions, they become
bioavailable.
Indeed, I am of the opinion that when combined with
hygroscopic salts (nitrates, chlorides), carbohydrates
create a microenvironment that sustains microbial
colonization of the property.
The question is how we block this growth of
Stachybotrys chartarum from occurring in the
昀椀rst instance and how do we block or reduce the
carbohydrate consumption by the mould.
We can use formulation changes to replace starch/
cellulose additives with the gypsum plaster and paint
products. Or use Pozzolanic binders or metakaolin
or silica fume can encapsulate organics within a
denser matrix.
We can also moisture control the environment, the
most critical factor — without water, carbohydrates
cannot be metabolized.
Stachybotrys chartarum is a fungus that digests
polysaccharides calcium and cellulose found in
materials like plaster, drywall.
•
Sodium salts (such as sodium sulphate) in plaster
can create osmotic stress or alkaline conditions,
which may initially make the environment less
favourable for some fungal growth, however
the sodium is not only a transport mechanism
for the moisture, but also, as a byproduct of
e昀툀orescence make nitrates available to the
Stachybotrys Chartarum as a food source.
•
When sodium levels are reduced for example,
through leaching or environmental changes
the limiting factor in the formation of the
mould, the substrate becomes less hostile, and
fungal enzymes can more e昀케ciently break down
polysaccharides.
•
Nitrate availability is key: Once sodium is
leached and nitrate remains, Stachybotrys
chartarum can digest the polysaccharides in the
material and colonise the property.
•
Sodium itself does not directly inhibit the
fungus from digesting polysaccharides; rather,
high sodium concentrations can slow down
fungal colonisation, but as sodium is reduced
and nitrate becomes available, the fungus gains
easier access to its food source.
Steps needed to Minimise Polysaccharides
in Plaster
We could use surface treatments Silane/siloxane
coatings reduce water uptake, indirectly blocking
carbohydrate activation.
1. Reduce Dosage of Organic Additives
Lower the amount of starch and cellulose ethers to
the minimum required for workable plaster. This
reduces the available nutrient source for fungi.
However Long-term mould prevention in gypsum/
paint systems comes from breaking the nutrient–
moisture chain at source. First, reduce the digestible
polysaccharide load by either lowering starch/
cellulose-ether dosage to the minimum that still
gives workable skim/昀氀ow, or replacing them
with non-nutritive rheology modi昀椀ers (synthetic
associative thickeners like polyacrylates/PU
thickeners, or inorganic thixotropies/clays) so you
keep spreadability, water retention and open time
without supplying edible carbons to the stachybotrys
Chartarum. Where rheology still needs organic
additives, immobilise/encapsulate them so they’re
not water-extractable and can’t migrate to the
surface during humidity cycling.
EXPERT WITNESS JOURNAL
•
2. Substitute with Non-Nutritive
Rheology Modi昀椀ers
Replace organic thickeners (like starch/cellulose)
with synthetic alternatives such as polyacrylates,
polyurethane thickeners, or inorganic thixotropes
(e.g., clays). These maintain workability without
supplying edible carbon.
3. Encapsulate Organic Additives
Use polymeric binders (acrylics, latex, PVA
emulsions) to encapsulate cellulose and starch
particles, making them less bioavailable to fungi.
120
JUNE 2026
