Expert Witness Journal Issue 64 December 2025 - Flipbook - Page 96
hygroscopicity. Paper facing degradation: High
pH ~11–12, (which the Stachybotrys Chartarum
likes) saponi昀椀es organic binders and weakens
cellulose, making the cellulose available to the
Stachybotrys Chartarum as a food source as well as
reduced sodium and increase in available calcium.
ɿ
Gypsum Chemistry
Gypsum
is
calcium
sulphate
dihydrate
(CaSO4·2H2O). Normally, gypsum is close to neutral
pH, but processing or contamination (e.g., alkaline
residues from plaster additives) can lower its pH. By
increasing acidity (lowering pH toward ~3-4), you:
Residue Formation After Bleaching:
•
•
•
•
•
Sodium salts (often sodium hydroxide or sodium
hypochlorite residues) remain embedded in the
paper matrix after bleaching.
These salts Increase surface conductivity paper
becomes more prone to electrostatic interactions
and moisture attraction.
Raise hygroscopicity the paper absorbs water
more readily, creating a microenvironment
favourable to mould colonization.
Reduces the sodium through leaching.
Makes available the cellulose and calcium as a
food source.
•
•
•
•
E昀昀ect on Stachybotrys Chartarum
High pH (11–12):
Promotes saponi昀椀cation of organic binders
(e.g., oils, resins, adhesives).
Weakens the structural integrity of cellulose
昀椀bres by breaking glycosidic bonds.
Stachybotrys Chartarum prefers alkaline to slightly
neutral substrates with abundant cellulose and
calcium. Acidic conditions Inhibit fungal enzyme
systems (e.g., cellulases and proteases), reduce
spore germination and hyphal growth. Shift the
ecological balance toward non-cellulolytic microbes
that outcompete Stachybotrys Chartarum, such as
penicillium spp
Resulting vulnerability:
•
•
Cellulose becomes more accessible as a nutrient
source.
Opportunistic fungi such as Stachybotrys
chartarum exploit this weakened cellulose,
accelerating biodeterioration.
Practical Considerations
Controlled acidi昀椀cation:
Use acidifying agents such as strong mineral acids,
Aim for a bu昀昀ered pH ~ 3-4, not extreme acidity, to
maintain material stability.
Microbiological Implications through
biological colonization pathways.
Stachybotrys chartarum thrives in moist, cellulose-rich,
alkaline and high calcium environments, through a
combination of:
•
•
•
•
Residual low sodium salts,
Moisture retention and leaching of sodium
High alkalinity binder breakdown exposed
cellulose and calcium.
Exposed cellulose and calcium as a food source
Which creates an ideal ecological niche for
colonization and sporulation of Stachybotrys
Chartarum on gypsum masonry walls.
Practical Considerations
•
Preventive conservation:
ɿ Do not use bleach to control Stachybotrys
chartarum
ɿ Increase the acidity of the gypsum to
control stachybotrys chartarum growth.
ɿ Do not neutralize or wash out residual
sodium salts.
EXPERT WITNESS JOURNAL
Reduce the solubility of cellulose breakdown
products.
Limit the availability of nutrients that fungi
exploit.
Create a less favourable environment for fungal
enzymatic activity.
Add this to the control humidity (
