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Chapter 4:Timber

1. Classification and Structure of a Tree:

1. Exogenous Trees: These Trees increase in bulk by growing outwards and distinct consecutive rings are formed in the horizontal section of such a tree. These rings are known as the annual rings because one such ring is added every year and these rings are used in predicting the age of tree. They are further divided into two groups:

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I. CONIFERS: THE CONIFERS ARE ALSO KNOWN AS THE EVER GREEN TREES AND LEAVES OF THESE TREES DO NOT FALL TILL NEW ONES ARE GROWN. THESE TREES YIELD SOFT WOODS WHICH ARE GENERALLY LIGHT COLOURED, LIGHT IN WEIGHT AND WEAK.

II. DECIDUOUS: THE DECIDUOUS TREES ARE ALSO KNOWN AS THE BROAD LEAF TREES AND LEAVES OF THESE TREES FALL IN AUTUMN AND NEW ONES APPEAR IN SPRING SEASON. THE TIMBER FOR ENGINEERING PROPOSE IS DERIVED FROM DECIDUOUS TREES.

III. ENDOGENOUS TREES: THESE TREES GROW INWARDS AND FIBROUS MASS IS SEEN IN THEIR LONGITUDINAL SECTIONS. THE TIMBER FROM THESE TREES HAS VERY LIMITED ENGINEERING APPLICATIONS. EXAMPLES – BAMBOO, CANE, PALM ETC.

Structure:

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2. DEFECTS IN TIMBER:

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Q - What are defects in timber ?A -Types of timber defects are as following:1. Knots2. Shakes3. Dry rot

1. KNOTS:

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1.1 KNOTS:

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1.2 KNOTS:

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• Where a branch has grown out of a tree the grain in the trunk becomes very twisted. When this is cut through during conversion the result is a weaker board and one which is difficult to work. Dead knots occur in some softwoods.

• These are distinguished from live knots because they show a black line round their circumference and they sometimes fall out of the wood leaving a hole.

1.3 KNOTS:

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2. SHAKES:

• These are splits along the grain of the wood.

• Heart shakes and star shakes are very similar; they radiate from the centre or heart (see drawing)

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2.1 SHAKES:

• Cup or ring shakes follow the annual rings.

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• End splits are caused by rapid drying from the end grain

• Shakes may occur during the felling or as a result of faulty seasoning.

2.2 SHAKES:

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3. DRY ROT:

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3.1 DRY ROT:

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• This is caused by a fungus growth which lives on the wood and thus destroys it. It attacks wood in damp, unventilated positions causing it to dry up and crumble into dust.

3. CLASS WORK:

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Questions:1.Show by means of sketches what you understand by the following: star

shake, knots, cup shake, waney edge ?2.Write down what you know about the common furniture beetle ?3.Name a fungus which destroys wood particular damp unventilated

position ?

The art of seasoning is to extract the moisture under controlled condition as nearly as possible at a uniform rate from all part of timber and to leave the remaining moisture that cannot be extracted uniformly distributed trough out the mass.

• Air Seasoning or Natural Seasoning

• Artificial Seasoningi. Water Seasoningii. Boiling or Steamingiii. Kiln Seasoningiv. Chemical Seasoningv. Electric Seasoningvi. Smoke Drying

As soon as the tree fall, it is converted by sawing into battens and planks etc. these are then stacked on a well drain place in shade, care is taken to ensure free circulation of air all around each piece. Stacking is done on masonry or concrete support a few centimeters Above ground. These process of seasoning timber is the best as it gives very strong and durable timber, but its is extremely slow. It takes more than 6 months for timber to season in moderate climates.

i. Water Seasoningii. Boiling or Steamingiii. Kiln Seasoningiv. Chemical Seasoningv. Electric Seasoningvi. Smoke Drying

Timber Immersed

Running Stream of Water(3 to 4 weeks)

Air to Dry

Timber Immersed

Boiled water(3 to 4 hours)

Steam spray

Air and dry

Timber log

Stacking

Heating(hot air and electric heater 3 days)

Air and dry

Timber log

Place salt

Absorbed moisture content from inside of timber

Natural seasoning

Timber log

Field electrodes

Transform high voltage current

Produces heat

Timber dry

Natural seasoning

Timber log

High density of smoke

Timber hard

Natural seasoning

5. PRESERVATION OF TIMBER

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• Timber has to be protected from the attach of insects e.g. white ants etc. and from internal decay due to dry and wet rots.

• Perfect seasoning is the most effective means of preservation. Timber should be well seasoned before application of preservatives as otherwise the preservations would block the pores of timber, thereby causing this decay due to entrapped moisture, Common method of preservation adopted are :-

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I. Charring:- Lower ends of posts that are to be embedded in ground area charged with a view of present dry rot attack of worms. It is done by quenching the ends of posts in water after they are charred on wood fire to depth o 1.5cm.

II. Tarring; It consists in coating with tar or tar mixed with pitch. Embedded portion of timber fence posts, ends of door and window frames, batters and beams built in wall area usually tarred.

III. Painting: A paint with applied to timber acts not only as a good preservative but also it enhances the appearance of the surface so treated. For e.g. So lignum.

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(iv)Creosoting: Creosote oil is a dark brown thick oily liquid. This is done in air tight chamber, after the air is exhausted from chamber the creosote oil is then pumped at a pressure of 9kg/sq cm and at a temp of 50 degree Celsius so long as the timber is not fully saturated with oil. It is used in railway sleepers. Piles and transmission poles, undesirable color and smell inability to take paint well and tendency to stain plaster limit its use.

(v) Wolman salt: This salt consist of creosote and sodium fluoride and is soluble in water. It is odorless and leaves no stain on wood. This renders the timber extremely fire resistant and destroy many kind o fungi.

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(vi)ASCU Treatment : Forest Research Institute, Dehradun has developed a new preservative know as ASCU . It is available in form of powder and is made up of three chemicals mixed in ratio given below :1 Part by weight of hydrated arsenic pent oxide (As2O5.2H2O)3 Part by weight of blue vitriol

(CuSO4.5H2O).4 Part of weight of potassium

dichromate (K2Cr2O7.2H2O) Six parts o this powder are mixed with 100 parts by weight

of water. ASCU solution can be applied or sprayed in two coats. This treated timber may be painted . Varnished, polished or waxed, the solution is odorless. This render timber immune to the attack of white ant.

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Six parts o this powder are mixed with 100 parts by weight of water. ASCU solution can be applied or sprayed in two coats. This treated timber may be painted . Varnished, polished or waxed, the solution is odorless. This render timber immune to the attack of white ant.

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• (vii) Fire proofing of timber :- Making timber fire proof is not possible , but fire resistant is possible up to sufficient extent.

• Soaking timber is ammonium sulphate, ammonium chloride, ammonia , phosphate, sodium arsenate,

Zinc chloride, etc or spraying on timber,

a solution of sodium silicate, potassium

silicate or ammonia phosphate etc. Imparts

fire resisting property.

• Abel's method of fire proofing timber is painting the surface first with a dilute solution silicate (Na2SiO6) then with a cream like paste of slaked fat lime and in the end with concentrated solution of silicate of soda.

ANY QUERY

CHAPTER 5MISCELLANEOUS MATERIALS

Topic: DISTEMPERING

1. DEFINATION: DISTEMPERS ARE CONSIDERED TO BE WATER PAINTS CONSISTING

OF WHITING GLUE OR CASEIN AS A BINDER & SUITABLE PROPORTION OF FAST COLOURING PIGMENTS. THESE DISTEMPER FORM A CHEAP AND DUARABLE AND EASILY APPLIED DECORATION FOR INTERNAL USE ON PLASTERED CEMENT CONCRETE AND VARIOUS WALL BOARD SURFACES.

2. COMPOSITIONS: A DISTEMPER IS COMPOSED OF BASE (WHITING OR

CHALK ), GLUE(BINDER), WATER(CARRIER OR THINNER ) AND COLOURING PIGMENT. DISTEMPER ARE AVAILBLE IN VARIOUS SHADES. THEY MAY BE EITHER IN POWDERFORM OR PASTE FORM . THESE ARE REQUIRED TO BE MIX WITH HOT WATER BEFORE USE .

3.VARIOUS FORMS: WHITE DISTEMPER COLOUR DISTEMPER OIL BOUND DISTEMPER CASEIN PAINTS

3.1 WHITE DISTEMPER:• MADE BY MIXING ONLY WHITING

& GLUE SIZE

3.2 COLOUR DISTEMPER:• PREPARED BY MIXING DESIRED

COLOUR PIGMENT TO WHITING BEFORE MIXING IT WITH GLUE SIZE

3.3 OIL BOUND DISTEMPER (OBD):• IT IS VARIETY OF OIL

PAINT IN WHICH THE DRYING OIL IS SO TREATED THAT IT MIX WITH WATER. SUCH DISTEMPERS ARE DILUTED OR THINNED WITH WATER WHEN REQUIRD THEY FORM ON DRYING A DURABLE & WASHABLE COATING.

3.4 CASEIN PAINT:

• PREPARED BY MIXING A FINELY GROUND CASEIN (IS EXERTED FROM MILK, CURD AND ACT AS A BINDER) WITH A WHITE BASE USUALLY SLAKED LIME. DUE TO HIGH OPACITY, THESE PAINT ARE USED ON THE PLASTERED SURFACES.

4. PROPERTIES: DISTEMPER MAY BE FORM OF OIL BOUND

WASHABLE PAINT, WASHABLE OIL FREE DISTEMPER, NON WASHABLE.

THEY ARE CHEAPER THEN PAINT AND VARNISHES.

THEY ARE TREATED LIKE WATER PAINTS AND HENCE ARE EASIER TO APPLY.

THEY ACT AS SEALER OVER POROUS SURFACES AND ALLOW THE WATER TO PASS THROUGH THEM. THIS PROPERTY PERMITS THE NEW WALL TO DRY OUT WITHOUT DAMAGING FILMS.

THEY ARE MORE DURABLE & PRESENT SMOOTHER.

THEY ARE PREFERRED TO COLOUR WASH AND WHITE WASH. THEY PROVIDE A GOOD REFLECTIVE COATING.

PREPARATION OF DISTEMPER

PROCESS OF DISTEMPERING• Various steps involved in process of distemper:

1.Preparation of surface

2.Priming coat

3.Coats of distemper

PREPARATION OF SURFACE(1) The new plastered surface should be kept exposed for a

period of two months or so to dry out before distemper is applied on them. The presence of dampness on the surface results in failure of distemper coating.

(2) The surface to receive distemper should be free from any efflorescence patches. These are to be wiped out by clean cloth.

(3) The cracks, holes seen on wall surface should be filled with putty and to allowed to be becomes hard before distemper is applied on the surface

(4) The old distemper should be removed by scraping and profuse watering before applying the new distemper.

PREPARATION OF SURFACE

PRIMING COAT• After proper preparation of surface, The next step is to apply priming coat . it is

allowed to dry .For local made distemper, the milk is used for priming coat. One liter of milk will cover about 10 m square of the surface.

COATS OF DISTEMPER • The first coat of distemper is then applied on the surface. It should be of a light and

applied with great care. The second coat of distemper is applied after the first coat has dried and become hard. The distemper should be done in dry weather to achieve better results.

5. DISADVANTAGES: 5.1:ON DRYING DISTEMPER FILMS LEADS TO CRACKING AND FLAKING DUE TO SHRINKAGE PROVIDE THAT THE RECEIVING SURFACE IS WEAK.

5.2: Distemper films are thicker and more brittle then other water paints

5.3: Distemper give poor result in damp place as alternative wetting and drying cause defects like peeling, flaking and plastering. distempering should not be done in damp weather.

TOPIC: PAINTS1. The main types of Paints are as following :• Aluminium paint• Anti corrosive paint• Asbestos paint• Cement paint• Emulsion paint• Enamel paint• Oil paint• Plastic paint• Silicate paint• Synthetic rubber paint

(A) ALUMINIUM PAINT

• It protects the iron & steel from corrosion in better way.• Possesses good weather resisting and water proofing qualities.• Due to its brilliant silvery shining texture it is visible even in darkness.• High spreading or covering power.

(B) ANTI CORROSIVE PAINT• They consist oil; a

strong drier colouring pigment mixed with very fine sand. They are cheaper to white land. It lasts for long period and give back appearance to surface

• Used for external work to protect and preserve structure steel work against adverse effect of weather fumes ,acid corrosive chemicals etc.

(C) ASBESTOS PAINT• Consists the fibrous asbestos as

the man ingredient of paint. It possesses the qualities of retarding the action of fire.

C: (A) ASBESTOS PAINT• Used for painting structural

steel and iron works under water also used for painting exterior brick and plastered surface.

C: (B) ASBESTOS PAINT• It is different from ordinary

oil paint and varnish. A cellulose paint hardens by evaporation of thinner or solvent used.

(D) CEMENT PAINT • Better water proofing qualities• Possesses good strength,

hardness density and durability• It exhibits excellent decorative

appearance.

(E) EMULSION PAINT• Used for brick and

masonry surface which contain free alkali the surface to be painted should first be washed with zinc sulphate solution.

(F) ENAMEL PAINT• T dry slowly, but on

drying, it produces a very hard, impervious, glossy and elastic, smooth and durable film over the surface being painted.

• Enamel painted surface is not affected by hot & cold water, steam, acid, alkalis, fumes of gas etc.

(G) OIL PAINT• This is ordinary paint consist of

base and vehicle may contain others such as drier, thinner, an inert filler and coloring pigments.

(H) PLASTIC PAINT

• Used for painting showrooms, auditoriums, offices, cinema halls etc. where attractive appearance is desired.

(I) SILICATE PAINT• On drying, forms a very

hard and durable surface.• Paint has no chemical

action.• No affected by alkali's.

(L) SYNTHETIC RUBBER PAINT• Excellent acid,

alkali and moisture resistance properties.

• Dries quickly and high covering power

• Moderate in cost and can be applied easily on surface.

HEALTH EFFECTS OF VOCS IN HEALTH EFFECTS OF VOCS IN PAINT FUMES:PAINT FUMES:

• There is a wide variety of both short-term and long-term negative health effects associated with VOCs in paint fumes. The severity of the health effect depends on several different factors, including both the length of time and the level of exposure. Some examples of short-term, temporary side effects include:

• Irritation of the eyes, nose, throat or and/or respiratory tract• Visual disturbances• Headaches• Loss of coordination• Nausea• Lightheadedness• Dizziness• Allergic skin reaction• Fatigue• Memory impairment

• Some of the conditions above can become chronic in individuals who are consistently exposed to VOCs in paint fumes either in the home or at work on a daily basis. Long-term health effects of VOCs can include:

• Liver damage• Kidney damage• Central nervous system damage• Certain types of cancer• Asthma

DO VOC’S DISAPPEAR WHEN DO VOC’S DISAPPEAR WHEN PAINT DRIES:PAINT DRIES:• The odor that emits from paint when it is freshly applied is

a result of the ingredients within the paint that turn it to a liquid substance. These substances are evaporated into the air while wet paint is drying. The more wet the paint, the more substances in the air and the stronger the odor. As the liquid part of the paint continues to evaporate, odorous paint fumes continue to form. Along with evaporation comes the process of dispersion.

• Dispersion occurs when the fumes mix with the air and are dispersed into the environment. As dispersion occurs, more and more of the fumes are carried throughout the air, which makes them less concentrated, and the odor less strong. When the fumes are completely dispersed, the paint is dried entirely and the odor eventually disappears. VOCs are at their highest concentration when paint is freshly wet.