Biodeterioration of wood - causative agents, how to prevent biodeterioration and assessment of biodeterioration.

1. Biodeterioration of wood
Ajimoon Nissa

2. What is Biodeterioration?
• Biodeterioration or biodegradation of
materials can be defined as any undesirable
change in the properties of a material caused
by the vital activities of biological agencies
organisms

3. Different types
• Biofouling which is in the form of deterioration
occurring when the mere presence of an organism or
its excrement renders the product unacceptable
• Chemical assimilatory biodeterioration occurring
when a material is degraded for its nutritive value

4. The Rot
 Causative organism is Fungi
 Wood being a vegetative material i.e. Cellulose and lignin
provides food for the saprophytic fungi.
 Looses strength, becomes soft & spongy.
 Joints, seams, places a where the grains are exposed cracks
in the wood are mostly affected.
 Two types –
 White Rot – Basidiomycetes – break lignin
 Brown Rot – Zygomycetes, Ascomycetes and Fungi impertectii
– consume sugar and other carbohydrates

7.  By discoloration of paints
 By sounding with hammer, dull sound
indicates fungal infection
 Pressed with finger in advanced stage,
powder comes out
 By drilling small holes in wood at different
places of the vessel

8.  Use of only seasoned wood for boat
construction
 Use of heart-wood always but not the soft-wood
or sap-wood.
 Allow proper ventillation into the vessel
 Infected wood should be replaced immediately
to prevent infection to other wooden members
 Avoid painting of the inner surfaces of the boat
below the water line
 Eliminate entry of water into the hull-planks

9. Borers
 log rafts, harbour piles and many other
waterfront structures.
 distributed throughout the salt waters.
 Two types - bivalve molluscs and crustaceans

10. Molluscan Borer
• Two families
– Teredinidae or the wood - boring shipworms,
– the pholadidae or rock borers
• Important genera of wood boring molluscs
are Teredo, Bankia, and Nausitoria
• The larvae make very small entrance holes on
the surface of the wood secreting a
protective calcareous lining for the burrow
• Commonly known as `shipworms’

11. Pholadidae
• Bore into wood, clay, soft rock, shells and even
into plastic and poor grades of concrete.
• Pholas and Martesia – in india M.striata and
M.fragilis is common

12. Crustacean Borer
• attack the wood making narrow galleries, which
seldom reach very deep
• Eroded away by wave action, which exposes
unattacked surface for fresh attack
• Important Orders `Amphipoda’ and `Isopoda’
• Genera – Limnoria, Sphaeroma and Chelura

13. How to Prevent?
 Keeping the vessel in freshwater for some duration so
that the marine borers would die
 Take the boat out of water & keep for 2-3 weeks, when
they die due to want of moisture
 By sheating through copper/aluminium/ FRP sheets
 By chemical treatment of wood by toxic preservatives
like coaltars, creosote etc

14. Fouler
• Does not destroy materials directly
• On immersion in seawater, fouling settlement starts
• A primary film or slime film (formed by bacteria,
fungi, diatoms and protozoa enmeshed in detritus), fixation
of larvae of macroscopic organisms (algae, tubeworms,
bryozoans, hydroids, barnacles, mollusks) and finally the
growth of the fouling community.
• Among these Barnacles especially Balanus deteriots
antifouling coating and allows corrosion

15. Effects of fouler
 roughness of hull
 fuel consumption are increased
 speed is reduced
 failure of antifouling coatings results in Corrioson
 Clogged Pipes & engine get heated up
 Reduces the efficiency of electronic devices like transducers
etc

16. How to Control
 By application of antifouling paints, the self-life of
paint varies from 6 months of 1 year
 Commonly Cuprous oxide, an inorganic toxicant
and tributyl tin oxide (TBTO) an organic toxicant
mostly used in the antifouling coatings
 Organometallic - TBTO and tributyl tin fluoride
(TBTF) provide 4 to 5 years of fouling free life
 By copper-sheathing, being poisonous & prevents
both the borers & foulers, but Al or FRP cannot
help
 By keeping the sea going vesels in freshwater for
some duration

17. Application
• TBT based antifouling paints must not be
applied to vessels of < 25 m in length
• biocide release rates less than 4 µg TBT cm -2
day -1
• copper based coatings must have a copper
release rate of less than 40 µg cm -2 day -1.

18.  Destructive testing- includes test procedures, which
destroy the test sample under assessment. Mechanical
strength testing and cutting opening the sample to see
the internal damage especially in natural materials like
wood come under this.
 Non-destructive testing - include procedures like X-
ray radiographs and visual observation of the surface of
the test sample. These methods do not destroy the test
sample and have the advantage of using the same sample
for further study
Assessment of Biodeterioration

19. Prevention
 Use of biocides to control the biological activity.
 Use of anticorrosive coatings and application of
Cathodic protection procedures.
 Upgradation of material.
 Use of physical barriers/wrappings.