Up Wood & Water Specific Gravity Mechanical Properties Enemies of Wood Tree Growth & Wood Quality

 

Enemies of Wood

 

A. Fungi - 

Plants that contain no chlorophyll and must take their food from other material.

 B. Insects -

 Either use wood for food, a place to live, or both.

 C. Marine Borers -

 In salt water - 2 mollusks and I crustacean

 D. Fire and Heat

 E. Weathering

  


 

Decay Fungi

Basidiomycetes

 

A. White Rot - attacks lignin, leaving mainly white cellulose.

 B. Brown Rot - attacks cellulose and hemicellulose, leaving mainly brown lignin.

 C. Dry Rot - special mycelial tubes bring water to wood.

  

They 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.

 

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Soft-Rot Fungi

Ascomycetes

 

Major cause of failure in hardwood transmission poles and other hardwood products that are in ground contact.

 Usually start on the outside of wet wood and works it way inward.  A slow and less obvious degradation.

 The problem is that the hyphae grow strictly within the cell wall and never enter the cell lumen or pits where many treatments are restricted.

 

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Staining Fungi

 

Do not destroy wood - only degrade it.

 The 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.

 Staining fungi live on sugars in cell lumen; therefore, hyphae are in lumens and through pits to other lumens.

 

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Mold and Mildew Fungi

 

Grows on surface of wood where moisture content is 20 - 25 percent.

 The mycellium are usually clear but the fruiting bodies are dark, giving the surface a very dirty look.

 


 

 Conditions required for fungal attack

 

A. Moisture -

most fungi will not attack wood that is below the FSP, especially below 20%.

 B. Temperature-

grow most rapidly between 70 and 90 degrees F. Inhibited below 32 degrees and above 1 00 degrees.  Killed by high temperatures in kilns.

 C. Oxygen-

need less than atmospheric amounts but if moisture content is high enough - not enough oxygen.

 D. Acidity-

pH of 4 to 6 for best growth

E. Food -

the wood itself - thiamine is necessary.

 

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Preventing Fungal Attack

 A. Keep wood dry -

1) keep wood indoors

2) prevent leaks

3) prevent condensation - ventilate

4) prevent contact with ground, concrete, or stone.

 B. Treat with a toxic chemical

 C. Use decay-resistant species

 


 

 Insects - Termites

 

Subterranean Termites-

Queen lives in ground up to 20 feet deep.  Workers tunnel to surface under a piece of wood and start eating it.

If 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.

Termites never work in the open.  Always in wood or tubes.

There are only two types of homes in East Texas: those with termites and those that are going to get termites.

FORMOSA Termites - subterranean termites on steroids.

Drywood Termites - Attack wood structures like telephone pole cross arms from the air.

 

 


 

 Insects -- 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.


 

Insects

Carpenter Ants

Carpenter Bees

 

Mainly looking for a home.

Ants - get between two wood members and wear away the wood surfaces creating a cavity that they use as home.

Bees - 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.

 


Conditions Required for

Insect Attack

 

Termites-

 A. Moisture - they will bring it in themselves if necessary.

 B. food - prefer wood already attacked by fungi but will attack sound wood.

 C. Shelter from exposure.

 

 Powder Post Beetles -

 Food - wood of the right species exposed outside.

 


Preventing Insect Attack

 Termites -

 A. avoid ground contact

 B. use termite shields and proper construction techniques

 C. Treat with toxic chemicals

1. Wood

2. Ground

 

Powder Post Beetles -

 A. dip treat fresh cut lumber in insecticide

 B. infested lumber needs to be:

1. Kiln dried (high temperature)

2. Fumigated

3. Burned

 


 Marine Borers

 

Mollusk --

1. Teredo (shipworms)

2. Pholads

bore 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

Crustacean -- Limnoria

Causes the most damage but is less catastrophic because it is done in the open.

The 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.

  

  


Conditions Required for

Marine Borer Attack

 

1. Saltwater or brackish water

 2. Wood

 

 

 

Preventing Marine Borer Attack

 

1. Use naturally durable species (none in USA)

2. Saturate with creosote

3. Dual treatment - treat to refusal with CCA, dry, then saturate with creosote.

 

 


 Fire and Heat

wood starts to decompose at temperatures above 100 degrees C.

 Above 200 degrees C - starts pyrolysis

 Above 270 degrees C - fire is self-sustaining

 

As 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.

 2-inch lumber will char in from both sides so that:

                 3/4 + 3/4 = 1 1/2 which equals the thickness of the piece.

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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.

 

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Conditions Required for

Fire Damage

 

1.     High temperature

2.     Oxygen

  

Preventing Fire Damage

 

Treat with a fire retardant - produces a 1/4 inch char layer that insulates and keeps out oxygen.

 


 

 Weathering

 

Caused by:

 1. Ultraviolet light

 2. Dew cycle

 3. Shrinking and swelling

 4. Soft-rot

 5. Abrasion from wind and rain

  

Conditions necessary:

 

exposed wood in outdoor environment

 

 Preventing weathering:

cover with a coat of paint or other protective finish.  Shield wood from ultraviolet rays and dew cycle.

 

 


 

 Wood Preservatives

 

Ideal Preservatives:

 1. Toxic to wide range of fungi

 2. High degree of permanence

 3. Ability to penetrate wood

 4. Non-corrosive to metal

 5. Safe to handle

 6. Economical

 

Basically 3 types of preservatives:

 A. Creosote - over 150 identifiable chemical compounds that are toxic to fungi

 B. Oil-Borne -

            1. Pentachlorophenol (Penta) may contain very small amounts of dioxin

             2. Penta WR - water repellant and light oil

             3. Copper naphthenate

 C. Water-Borne

1. CCA - types 1, 2, or 3

2. ACA

3. ACC

4. CZC

5. Boron salts

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Select the correct:

 

A. Preservative -- each type of preservative has it's advantages and drawbacks:

 1. 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.

              2. Penta will not kill marine borers

             3. CCA will not treat hardwoods sufficiently (Outlawed for home and playground uses)

 B. Penetration very seldom you can treat the whole object; therefore, you must have a treated shell of sufficient thickness.

 C. Retention -- Amount or volume of preservative per unit volume of wood.  Different uses require different retentions to ensure proper protection.

 

 


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.

 

Wood Preservative Treatments

 

All 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 viewpoint.

 I. Non-pressure Processes

 Non-pressure 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.

(A) 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.

Even 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.

 (B) 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.

 (C) 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.

 Cold 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.

 In 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.

(D) 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.

 The 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.

 Though 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.

(E) 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.

As 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.

Diffusion 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.

 2.  Pressure Processes

 The 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.

 The 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 cylinders.

 Accessory 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.

 Pre-treatment 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 chemicals.

 The 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.

 (A) 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 cylinder.

 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 treated timber.

 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.

 (B) 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 Textbook.

 In 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.

 

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