Illustration 1:
Mould on silicone sealant
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Mould fungus on sealants -
causes, countermeasures and prevention
The attack on elastic sealants by mould is a constant concern.
Mould attacks can be recognised from the incidence of mainly dark
spots on the surface of the sealant. The spots are usually black, as
in the case of the well-known mould "Aspergillus Niger," but can
also be brown, yellow, violet, red or pink.
Fungi are a large group of micro organisms. There are estimated to
be about 250,000 different types of fungus with around 50,000 of
them being mould fungi. The visible spots on the sealant are
metabolic products of these micro-organisms.
1. Causes
Illustration 2: Schematic representation of the
agglomaration of a mould fungus on a sealant.
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Illustration 3: Schematic representation of a
primary attack.
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Illustration 4: Schematic representation of a
secondary attack.
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The following conditions help to form mould on sealants:
- High air humidity with little movement of air. e.g. in
bathrooms, showers, kitchens etc.
- Warmth
- Nutrients in the form of organic deposits. e.g. residues from
body care materials such as soap, shower gel etc.
Since elastic silicone joints have low thermal conductivity they
are the warmest part of a tiled surface and where mould thrives
best, in combination with organic residues and moisture.
Mould fungus spreads through spores. Spores are mostly small
round cells with a diameter of a fraction of a millimetre and a mass
of a billionth of a gram. They are spread by the wind like dust
particles and are very resistant and long-lived. When they first land on, for example, a silicone joint where the
three factors for growth exist (humidity, warmth and nutrients), the
spores initially absorb water and enlarge by swelling in volume (see
illustration 2).
Then a thread-like filament grows out of the spore and spreads
by lateral branching in a circle around the germinating spore. A
network of filaments forms. These so-called mycelia (networks of filaments) can grow very
rapidly and thrive under favourable conditions. If mould is only
growing on the organic deposits on the sealant surface, it is called
a primary attack (see illustration 3).
These mould fungi
secrete a type of digestive juice which is able to break the sealant
down into usable decomposition products for the mould. If this
occurs, the mould can grow into the sealant. This is called a
secondary attack, which in the end results in the unattractive spots
on the silicone joint (see illustration 4.)
2. Countermeasures
Roberts Designs provides fungicidal (mould resistant) properties
to the sanitary silicone Maxisil A Ceramic, to the swimming pool silicone Maxisil P and to the natural stone silicone Maxisil N.
By using a
fungicidal formulation, mould attack is prevented as far as
possible. To ensure the sealants are physiologically safe, Roberts
Designs only uses fungicides that do not contain any toxic heavy
metal compounds or any other toxic substances.
A problem in making
fungicidal formulations of sealants by using additives is that the
anti-fungal effect cannot be guaranteed to be long-lasting, since
the protective agents can be consumed themselves (taken up my mould
fungi) as a result of their mode of action.
3. Prevention
The best means of prevention against mould on sealants is good
ventilation as well as regular cleaning and disinfection of the
elastic joints. Nothing can be done about the spores occurring
naturally everywhere in the air. However, the colonisation and
multiplication of micro organisms on the sealant can be prevented if
the rooms are well ventilated and the elastic joints are properly
looked after.
In addition to regular cleaning, the elastic joints should be
treated at definite intervals (e.g. weekly) with a commercial
disinfectant. For cleaning, preferably neutral or alkaline cleaning
agents should be used, since mould spreads more vigorously under
acid conditions.
If a mould attack occurs, as long as it is just limited to the
surface (primary attack), it should be treated with anti-fungal
spray from Roberts Designs. If the mould has already entered into
the sealant (secondary attack), the sealant must be removed
completely.
Before applying the replacement, the affected joint areas should
be treated with anti-fungal spray in order to remove any fungus
spores present. Otherwise, if any spores are still present around
the joints, fungal attack may very rapidly reoccur in spite of the
new sealant having fungicidal properties.
Should you have any further questions regarding this topic our
technical department will always be at your disposal.
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