Enemies of Wood
A. Fungi -
that contain no chlorophyll and must take their food from other material.
use wood for food, a place to live, or both.
Marine Borers -
salt water - 2 mollusks and I crustacean
Fire and Heat
White Rot - attacks lignin, leaving mainly white cellulose.
Brown Rot - attacks cellulose and hemicellulose, leaving mainly brown lignin.
Dry Rot - special mycelial tubes bring water to wood.
start as a spore that comes in contact with moist wood.
They germinate and start producing long, thin, thread-like segments
called hyphae. The hyphae enter the
wood through end grain or ends of cut wood cells.
The hyphae grow through the cell lumen and pits, into other cells.
As the hyphae further develop, they produce enzymes that allow them to
"eat" their way through cell walls creating bore holes.
Enzymes are then produced along the sides of the hyphae which allows them
to destroy the cell wall.
Major cause of failure in hardwood transmission poles and other hardwood products that are in ground contact.
start on the outside of wet wood and works it way inward.
A slow and less obvious degradation.
problem is that the hyphae grow strictly within the cell wall and never enter
the cell lumen or pits where many treatments are restricted.
not destroy wood - only degrade it.
dark color of the hyphae causes the wood to look blue or black thus losing its
appearance value. Also, because it
destroys the pit membranes, it makes the wood more permeable.
fungi live on sugars in cell lumen; therefore, hyphae are in lumens and through
pits to other lumens.
and Mildew Fungi
on surface of wood where moisture content is 20 - 25 percent.
mycellium are usually clear but the fruiting bodies are dark, giving the surface
a very dirty look.
required for fungal attack
fungi will not attack wood that is below the FSP, especially below 20%.
most rapidly between 70 and 90 degrees F. Inhibited below 32 degrees and above 1
00 degrees. Killed by high
temperatures in kilns.
less than atmospheric amounts but if moisture content is high enough - not
of 4 to 6 for best growth
wood itself - thiamine is necessary.
Keep wood dry -
keep wood indoors
prevent condensation - ventilate
prevent contact with ground, concrete, or stone.
Treat with a toxic chemical
Use decay-resistant species
lives in ground up to 20 feet deep. Workers
tunnel to surface under a piece of wood and start eating it.
they can't reach wood from ground, they build tubes of dirt up to the wood.
Some tubes are self-supporting and reach up to 2 feet.
Others are attached to other structure such as block wall and have been
known to go up 8 feet to reach wood.
never work in the open. Always in
wood or tubes.
are only two types of homes in East Texas: those with termites and those that
are going to get termites.
Termites - subterranean termites on steroids.
Termites - Attack wood structures like telephone pole cross arms from the air.
-- Powder Post Beetles
Adults lays eggs in open pores of wood.
Larvae eat into wood causing honeycomb.
After pupating and becoming adults, they bore out of the wood leaving
behind small holes and a pile of powder or "sawdust".
The different types of powder post beetles are given in Table 11.1. on Page 267 in Textbook.
One type attacks ring-porous hardwoods; therefore, ash and hickory
handles of tools left outside are susceptible.
Also, lumber stacked in air drying yards.
Infested firewood brought into the house at the right time can cause
infestation into furniture and paneling.
See Figure 11.9 on Page 267 of Textbook.
See Figure 11.9 on Page 267 of Textbook.
looking for a home.
- get between two wood members and wear away the wood surfaces creating a cavity
that they use as home.
- bore cross grain into a wood member, once in the middle, turn and bore both
direction along the grain. Leaving
a perfectly smooth, perfectly round hole about 1/2inch in diameter.
Moisture - they will bring it in themselves if necessary.
food - prefer wood already attacked by fungi but will attack sound wood.
Shelter from exposure.
Post Beetles -
- wood of the right species exposed outside.
avoid ground contact
use termite shields and proper construction techniques
Treat with toxic chemicals
Post Beetles -
dip treat fresh cut lumber in insecticide
infested lumber needs to be:
Kiln dried (high temperature)
tiny hole into wood and as they grow, they keep eating longitudinally, getting
fatter and longer with tails remaining near initial opening.
Some shipworms will get 2 feet long.
See Figure 11.10 on Page 269 in the Textbook
the most damage but is less catastrophic because it is done in the open.
attack takes place between the water levels at low tide and high tide.
They attack the surface of the wood and slowly grind it away.
Saltwater or brackish water
Marine Borer Attack
Use naturally durable species (none in USA)
Saturate with creosote
Dual treatment - treat to refusal with CCA, dry, then saturate with creosote.
starts to decompose at temperatures above 100 degrees C.
200 degrees C - starts pyrolysis
270 degrees C - fire is self-sustaining
a piece of wood burns, it forms a char around the outside.
If there is no external heat source, once the char is 3/4 inch thick, the
fire will go out.
lumber will char in from both sides so that:
3/4 + 3/4 = 1 1/2 which equals the thickness of the piece.
One of my favorite pictures. After the fire is out, the wood is still holding and the metal beams have collapsed.
|Two beams, one was wood and the other was steel, where placed in a test building. Fire was supplied for a half hour and the steel beam collapsed. Firemen stood on the wood beam and put the fire out.|
with a fire retardant - produces a 1/4 inch char layer that insulates and keeps
Shrinking and swelling
Abrasion from wind and rain
wood in outdoor environment
with a coat of paint or other protective finish. Shield wood from ultraviolet rays and dew cycle.
Toxic to wide range of fungi
High degree of permanence
Ability to penetrate wood
Non-corrosive to metal
Safe to handle
3 types of preservatives:
Creosote - over 150 identifiable chemical compounds that are toxic to fungi
1. Pentachlorophenol (Penta) – may contain very small amounts of dioxin
2. Penta WR - water repellant and light oil
3. Copper naphthenate
CCA - types 1, 2, or 3
each type of preservative has it's advantages and drawbacks:
Creosote is very good preservative for all needs except: it smells greatly; it
burns exposed skin; must be kept in a heated container for treatment.
3. CCA will not treat hardwoods sufficiently (Outlawed for home and
(Outlawed for home and playground uses)
very seldom you can treat the whole object; therefore, you must have a
treated shell of sufficient thickness.
In the 1970"s, I was working in Texas and part of my job was to develop a 40 page handout on wood and wood products for college students. The following is a copy of the section on preservative treatments. Things have changed since then and anyone now wishing to treat at home has to be a registered pesticide applicator. But the information is still worth knowing.
of the wood preservation processes in current use can be placed under one of the
following categories: non-pressure/ diffusion,, sap replacement, or pressure and
vacuum impregnation. Cost is often
a major consideration. The simplest
Processing method generally requires the least expensive equipment, but at the
some time, it is often the least effective for long term protection of the
material. However,, for some requirements it is not necessary to extend the
service life of untreated material. So
the choice of wood preservative and application method depends upon many
factors, each of which should be considered from the technological and economic
processes include any method where no external pressure is applied to force the
wood preservative into the timber. These
include brushing, spraying, dipping, steeping, cold socking, and hot-and-cold
both. Diffusion method can also be
considered in this category.
Brushing or spraying -The application of wood preservatives by brushing,
painting, or spraying i simplest treatment available. It requires a minimum investment in equipment and can be
employed for applying oil-borne and waterborne preservative chemicals, coat-tar
cresote or other low viscosity oils. This
method permits treatment to be carried out at the construction site or on wood
parts already in service.
when used in treating well seasoned material, the effect of brush or spray
treatments is superficial. They
cannot be recommended except as temporary expedients. The moderate penetration
that results is seldom more than a few millimeters in depth. If any physical
damage should rupture the thin protective shell, the piece is subject to attack
through the open area. Water-borne
chemicals are readily leached out of such timbers if they are in the open, but
oily materials should provide protection for somewhat longer periods.
Under optimum conditions the normal service life of the wood can be
extended one to three years, assuming that surface cracks and checks are
thoroughly filled and that generous quantities of preservatives are applied over
the entire surface of the timber.
Dipping - Another non-pressure process for applying preservative material
is dipping - This method involves the immersion of wood in a treating solution
for a period of a few seconds to a few minutes.
It provides little more effectiveness than brushing or spraying except
that end penetration is frequently better in easily treated species.
Complete immersion probably provides greater uniformity of coverage than
brushing and gives more assurance that all checks are filled.
Dip treatment is not effective if the wood is at a moisture content above
the fiber saturation point. Dipping has been found to be particularly well
suitable for the treatment of millwork such as window sash at the factory.
Paintable preservative in a non-swelling carrier (NSP), of which
pentachlorophenol is a good example, is widely used.
Dipping times are approximately three minutes.
Dip treatment extends service life two to four years when the wood is not
subjected to physical damage.
Steeping and Cold Soaking - Steeping and cold soaking are merely
prolonged immersions of wood in preservative solutions.
The term cold soaking is generally applied to the use of oil solutions
while steeping refers to the soaking of wood in water solutions of preservative.
soaking has been shown to be a rather effective method of treating seasoned
material for farm use because of this simplicity. Fuel oil solutions of pentachlorophenol are commonly
employed. The more viscous oils are
not as satisfactory unless heated to reduce viscosity. Soaking times are not critical and may be extended for long
periods although two to several days is usually sufficient.
Actually, a large proportion of the absorption takes place during the
first day of treatment, but prolonged soaking does increase depth of penetration
and amount of retention. As would be expected from anatomical considerations,,
the sapwood of certain softwoods is easily treated by this method.
Hardwoods having tylosis free vessels show good end penetration, but
generally poor transverse penetration.
the steeping process it is possible to use green as well as seasoned timber
because salt from the treating solution can move into wet wood by diffusion.
Seasoned timber absorbs both water and salt so that lower concentrations
of salt solutions can be used. When
treating green material, stronger solutions should be used to offset the
dilution and to speed up the rate of diffusion.
Hot-and-Cold Bath - The hot-and-cold bath process is undoubtedly the most
effective of the so-called non-pressure treatments.
The effectiveness of the method can actually be attributed to the mild vacuum
which is produced by the process, through not by mechanical equipment.
The poles, posts, or other timbers are first heated in preservative
solution, or in a dry kiln in some cases. This
causes the air in the cells of the outer layer of the wood to expand.
The heated material is then transferred to the cold preservative
solution. The warm air in the wood
cells contracts upon cooling and creates a partial vacuum in the outer portions
of the wood. As atmospheric
pressure tends to satisfy this mild vacuum, penetration of preservative into the
wood is aided.
mechanics of the operation are very flexible and can be adjusted to the
conditions at hand. Heating can be
accomplished in a kiln, in a tank of preservative or in water, depending on the
choice of treating chemical. The
material being treated need not be removed from the hot tank if the solution can
be pumped out and quickly replaced by cold preservative.
Though possibly not quite as effective, the hot liquid can simply be
allowed to cool.
coal-tar creosote and other preservative oils are generally used in this
treatment process, water-soluble salts can also be applied very effectively by
this method. Care must be exercised to limit the temperature of the hot both to
a level that is safe for the particular solution being employed while the cold
bath must be warm enough to ensure liquid flow.
If too high temperatures are reached, the oily preservatives are likely
to evaporate, Water solutions are subject to this danger as well as to the
possibility of precipitating part of the salts out of solution.
The recommended temperatures are 190'F to 2350 for the hot both and 90OF
to 150OF for the cold bath.
Diffusion Method - In the diffusion method of treatment, green timber is
gradually penetrated by a water-soluble salt which is generally applied in
concentrated form. The best known
example is the Osmose process in which the toxic chemicals in paste form are
coated over the surface of green, peeled timber. Over a period of weeks the preservative diffuses into the
green wood, provided the timber is stacked and carefully covered to prevent
moisture loss. Variation of this
method include the use of preservative bandages which are wrapped around
individual poles, either after an application of chemicals, or with a layer of
preservative lining the bandage itself. The
purpose of the bandage is to prevent the loss of moisture from the unseasoned
timber and to keep a supply of chemicals in contact with the wood.
with other non-pressure treatment methods, there is not great degree of control
over depth of penetration except through duration of stacking.
Duration of treatment can be adjusted from about 30 days for small
material to 90 days for timbers requiring greater penetration.
treatment is also employed in the protection of the groundline zone of standing
poles. Holes are bored into the poles near the groundline, preservative is
introduced into them and then the holes are plugged. The toxic chemical is believed to diffuse through this
critical zone over a period of time.
preservative treatment of wood by pressure methods is the preferred commercial
approach because of its greater efficiency and effectiveness.
Its efficiency stems from the much closer control over treating
conditions than is possible with the non-pressure processes.
Its effectiveness is due to the more uniform, deeper penetration and
greater absorption of preservative than can usually be attained by other means.
The fact that the timber is totally enclosed in a cylinder in which
conditions can be varied widely offers a great advantage.
cylinder is the heart of a pressure treating plant. It is a steel tank, usually horizontal, designed to withstand
high working pressures. Door may be
installed at either or both ends of the cylinder, depending on its size, the
nature of the material to be treated in it, and the loading system used.
In the treatment of poles, pilings, and other large timbers, the charge
can be rolled into the cylinder on standard or narrow gauge rail trams and
rolled out of the cylinder to the yards. Hand
loading or crane systems, are used for smaller material and small treating
equipment must be provided for heating and storing preservative, for
transferring it in and out of the treating cylinder and for measuring the amount
of preservative consumed in treating a charge. In addition, compressors and pumps are required for vacuum
and pressure phases of the treating schedule and gauges must be installed to
indicate those conditions.
with steam, vacuum or air pressure permits a greater range of control over the
final treatment with preservative. Each
of the well-known treating methods using pressure is based on a variation in
treating schedule of one or more of the above factors.
The desired method is selected because of its characteristic preservative
retention which in turn can be related directly to the cost of treatment
terms "empty-cell process" and "full-cell process" are
frequently applied to treatments by pressure methods. Though these terms may not be strictly accurate, they can be
applied in a relative way in describing the effect of a particular treatment
schedule. Cell lumens in the
penetrated portions of the wood treated by the full-cell process are supposedly
full of preservative. In the
empty-cell process the lumen walls are left with only a coating of chemical.
Diffusion from the lumen into the cell wall must take place in both cases
but it would be expected that greater concentrations of preservative would
ultimately be found in the walls of wood treated by the full-cell process.
Full-Cell Process - The primary objective of a full-cell treatment is to
attain maximum retention of preservative in the treated portion of the lumber.
The factor which distinguishes it from empty-cell treatment is the
preliminary vacuum which is designed to remove as much air from the cells as
possible, thereby removing the air cushion which resists preservative
penetration. A further advantage is
that there is a minimizing of preservative release ("kick-back")'
caused by the expansion of trapped air when pressure is removed from the
Bethell process is a full-cell process that is employed in treating with oils.
A preliminary vacuum is applied to the charge and held for a period of
time. Then, without releasing the
vacuum, the cylinder is filled with preservative and pressure is applied and
maintained until the desired absorption is reached.
After the preservative has been drained from the cylinder, it is
customary to apply a mild final vacuum to reduce preservative dripping from the
high net retentions attainable with the full-cell process can result in rather
high preservative costs. Its use
can be justified for marine applications where maximum retentions of creosote
are necessary for effective protection. In
certain tropical situations the high costs are also justifiable.
However, in many other uses,, the service life obtained from the timber
treated by the empty-cell process is adequate and the treatment costs are lower.
Empty-Cell Processes - The empty-cell process differs from the full-cell
process in that some means of recovering much of the preservative is used,
leaving no liquid preservative in the cell lumens of the treated portions of the
wood. In the original Rueping
process, this is accomplished by applying compressed air to the timber before
forcing the preservative into it. The
preservative can be admitted into the treating cylinder from an equalizing tank
where the air in the cylinder can interchange with the preservative.
This procedure traps air in the cells and when the pressure is released
after treatment, the trapped air expands and forces the preservative out.
A final vacuum serves to remove even more of the solution.
A diagram of the Rueping process is shown in Figure 11.12. on Page 282 in
A diagram of the Rueping process is shown in Figure 11.12. on Page 282 in Textbook.
the Lowry process there is no preliminary air pressure applied, but the schedule
is otherwise the same as for the Rueping process.
This eliminates the need for an air compressor.