Interior Materials

Compare ‘POP ceiling’ with ‘Suspended Al T ceiling or modular ceiling’.

2013-09-01T07:58:00.001-07:00

Sr. No.	POP ceiling	Aluminium ‘T’ ceiling
1.	Made with GI frame work and POP tiles	Made with Aluminium T framework and tiles [of either particleboard or fibreboard or Thermocole or plastic sheets or POP or Mineral wool tiles] are just placed in the frame work.
2.	Curved profiles are possible & very common.	Curved profiles are not possible.
3.	Cornices are made easily.	Cornices of this material are not possible.
4.	Relatively heavy weight ceiling.	Very light in weight with low density fiber or plastic or Thermocole or Phenotherm tiles or Mineral wool tiles.
5.	Takes relatively longer time for erection.	Takes relatively short time for erection.
6.	Access above the ceiling is virtually ruled out.	Access above the ceiling after erection is easy & without damage.
7.	Can develop cracks due to vibrations of the floor.	Cracks cannot be developed since the tile fitment is loose.
8.	Much cheaper than Al ‘T’ ceiling. Costs around Rs. 450=00 /Sq. Met.	Costlier than POP ceiling. Costs around 750=00 Rs. / Sq. Met.

Explain seasoning of timber.

2013-08-31T08:30:00.001-07:00

              Timber contains water. Timber does require a definite percentage of water in it, in order to retain its fibers strongly adhered to each other.
               Timber releases a part of this moisture in dry and hot atmosphere. And absorbs moisture in cold and humid conditions. This absorption and release, makes the timber bent, warped, shrunk or swollen etc. This change in the shape of a member can endanger the structure of which it is a part of.
               It has been found that if the percentage of moisture is controlled to a certain level, there is a least transfer of water between the timber and the atmosphere. And thereby the structure is prevented from damaging or deforming. This percentage to be controlled depends upon tropical conditions where the timber is to be used.

‘Controlling water percentage in timber to an extent that least moisture transfers take place between timber and environment, for the given ambient conditions’, is called as ‘Seasoning’.

Moisture content = Weight of water in timber.

Weight of dry timber.

Moisture content in the felled tree is 50 %. The desired moisture content for timber in Asian countries is between 10 to 20 %. For Mumbai, a humid place, it is 17 to 20%. For Nagpur, a dry place, it is 10 to 12%. And for Pune, a moderate place, it is 14 to 16%.

In order to control moisture in sawn timber sections, there are two methods:

1. Natural / air seasoning method.

2. Artificial seasoning methods.

1. Natural / air seasoning method.

Swan timber sections are stacked horizontally on a 30cm raised platform as shown. These are arranged in layers one above other. The layers are separated by sound dry wood spacers. Gap of about 50cm is kept between two adjoining members for free air circulation. Roof covers the stack and the timber is not exposed to direct sunlight or dew. The process of seasoning is very slow & takes even upto 2 years. Capital cost and operating costs are least in this method.

2) Artificial seasoning:

There are various methods of artificial seasoning as follows:

a) Kiln seasoning

b) Chemical seasoning

c) Electrical seasoning

d) Water seasoning

e) Boiling

Brief information of above methods is as under:

a) Kiln seasoning:

In this method, the drying of timber is carried-out inside an airtight chamber or oven. Timber is placed in such a way that free air circulates around. The steam is first forced inside in order to control the termites. Then the temperature is raised and maintained till the desired degree of moisture content is attained. The kiln seasoning, though costly, gives well seasoned timber as it controls three important conditions, namely, circulating air, humidity and temperature.

b) Chemical seasoning: This is also known as the salt seasoning. In this the timber is immersed in a solution of suitable salt. The salt is hygroscopic in nature and attracts the water content of timber. This water is then wiped out by cloth. But this method affects the elasticity and strength of wood.

c) Electrical seasoning: In this method, the use is made of high frequency alternating currents. The timber, when it is green, offers less resistance to the flow of electric current. The resistance increases as the wood dries internally which also results in the production of heat. This is the most rapid method of seasoning. But the initial and maintenance costs are so high that it becomes uneconomical to season timber on commercial base by this method.

d) Water seasoning: In this method the timber is cut in suitable sizes and immersed wholly in water, preferably in running water. The timber is taken out after 2 to 4 weeks. During this period the sap contained in wood is washed away. Then the timber is allowed to dry under a shed having free circulation of air. And the timber is seasoned.

e] Boiling: In this method the timber is immersed in water and then it is boiled. This is a very quick method. The timber is boiled for three to four hours. Then it is dried very slowly in shed. The periods of seasoning and shrinkage are reduced by this method, but its affects the elasticity and Strength of wood. This method is costly as compared to others.

What are the advantages of pre-cast slabs over slabs cast on site?

2013-08-29T01:39:00.000-07:00

The advantages of pre-cast slabs are following

1. Pre-cast slabs are light in weight compared to the slabs cast on site. Hence the structure gets less loaded with pre-cast slabs.

2. Quality of the pre-cast slabs is well controlled since the job is carried under skilled supervision.

3. Casting and curing time for a slab cast on site is at least one moth. Installing a pre-cast slab takes hardly a day or two. Hence installing pre-cast slab in an occupied tenement / shop / office is a much better solution.

4. The pre-cast slabs can be dismantled and reused somewhere else.

5. No centering structures are needed for pre-cast slabs.

Teak wood window compared with MS window

2012-04-22T19:51:00.001-07:00

Compare the advantages and disadvantages of a wooden window with an MS window.

ANS.

Sr. No.	Teak Wood Window	M S Window
1.	Looks elegant, if maintained well	Looks may not be appealing
2.	Can be polished or painted	Can be painted only. Before installing it could be powder coated.
3.	Gaps/ air leakages can be sealed better.	Probability for Gaps and air leakages is more
4.	Can bend, twist, rotten if not maintained well.	Can rust if not maintained well.
5.	Cost wise more ( Almost 3 times MS window )	Relatively much cheaper.
6.	Has a life of 70 & 80 years even if maintained well. Members are brittle later.	Has an infinite life if maintained well.
7.	It is strong enough, but not as strong as MS window.	Stronger than TW window.
8.	Catches fire.	Does not catch fire.

Wooden staircase V/s RCC staircase

2012-04-22T19:39:00.002-07:00

Compare the advantages and disadvantages of the Wooden Staircase over the RCC staircase.

Sr. No.	Wooden Staircase	RCC Staircase
1	Wooden staircase is relatively weaker.	RCC staircase is relatively stronger.
2	Construction time is relatively less.	Cement setting takes at least 21 days. Hence construction time is more.
3	Timber has a life. It becomes weak after about 70 to 80 years	RCC hardens with age. The process of hardening continues forever increasing its strength.
4	The appearance and the colour of the timber can be attractive.	RCC staircase can be made attractive by cladding and other decorations.
5	Timber staircases are light in weight	These are heavier in weight.
6	Timber is costlier than RCC.	RCC is cheaper than timber.
7	These are fire hazardous	These cannot catch fire.
8	These are sound and heat insulators.	Comparatively lesser insulators.

Advantages of a PVC carpet floor over woolen carpet floor

2012-04-21T16:44:00.002-07:00

What are the advantages of a PVC carpet floor over woollen carpet

floor?

ANS.

1. PVC flooring can be easily cleaned whereas; cleaning of woollen

flooring is a tedious job. For cleaning of woollen carpet, wet cleaning

is ruled out, and for dust removal, vacuum cleaner is needed.

2. PVC flooring does not get damaged due to water or by mild acids or

mild alkalies. Whereas woollen flooring becomes wet with water and

can create unhealthy situation due to rottening of jute backing cloth.

3. PVC flooring is available in many colours, designs, sizes and in tile

forms. There is a limitation of colours and design in woollen flooring.

4. Woollen flooring is much expensive as compared to PVC flooring.

Carpet, rug and durry

2012-04-21T15:42:00.001-07:00

Explain carpet, rug and durry.

Carpet: Carpet is normally referred to floor coverings when it is laid for the entire room, from wall to wall. Carpets are made of wool yarn or synthetic yarn. These can be woven, knitted or hand-made. There is backing layer of Jute cloth to attain the needed stiffness and weight.

Carpets are pasted to the floor, not rigorously but intermittently. To attain further softening, many times an under-layer of synthetic foam is pasted to the floor before laying the main carpet. This under-layer may be of U foam (Flexible PU foam) or coir foam or some similar material.

Carpets are excellent thermal and sound insulators. For acoustic control these are one of the best.

Rug:

The difference between carpet and rug is that the rugs are easily transportable and carpet is not. Also rugs are never pasted to floor and do not cover the entire room. Rugs are placed on selective portion of the room, say for seating area or for sleeping area. Woollen rugs of Kashmir are famous worldwide for their attractive design patterns and wool quality. Apart from wool and synthetic yarn, rugs can be of Jute, cotton or coir. These are also good heat and sound insulators.

Durry:

Durries are similar to carpets and rugs except that these have no backing layer of Jute. And hence both sides are attractive. Also durries can be as small as o 300 x 300 mm. Durries can be very large also that these can be placed in an Auditorium with no chairs. Durries can be folded and transported. These are made of either Jute or cotton or wool. These are also good heat and sound insulators.

Rubber Foam, U foam and Coir foam.

2012-04-21T12:58:00.001-07:00

Explain the terms Rubber Foam, U foam and Coir foam.

ANS.

i. Rubber Foam:

This is made out of natural rubber and while rubber is getting solidified, air is entrained. These are available in slabs measuring 2m x 1m and thickness varying from 12mm to 100mm. In addition to the air entrained minute cavities, it has half holes on one side of about 10 mm to 25mm diameter and in section it looks like an inverted U.

Rubber foam is used as cushioning material for sofas, chairs, padding and beds. It was the most popular foam in earlier days, but with the evolution of plastics, the ‘U’ foam has almost replaced Rubber foam. Rubber foam helps to some extent in absorbing sweats. Rubber foam has a life of 5 to 10 years and starts crumbling to powder later. It does generate marginal sag on sofa seats or beds due to a prolonged use.

ii. U Foam or Flexible PU foam:

U foam is artificial foam used in cushioning & padding. It is Synthetic and plastic product created by entraining air in Synthetic resins. It is available in various densities and it can be softer or harder to any extent. It does not deform due to repeated use. It is nonabsorbent and hence does not absorb sweat. It is available in slabs measuring 2m x 1m and thicknesses available are from 6 mm to 100mm. It has an infinite life.

iii. Coir Foam:

Coir foam is made by mixing molten rubber and coir. Thus the slabs made are a mixture of Rubber & Coir. The slabs of size 2m x 1m are available in thickness ranging from 25mm to 100 mm. This has a larger deformation coefficient and is used in cheap sofas / beds etc. It sags in one year only.

Window draping varieties

2012-04-20T19:42:00.001-07:00

What are the alternative window covering other than curtains?

Describe briefly.

Ans.

Other than curtains, following are the alternatives for windows covering-

1) Vertical venetian blinds.

2) Horizontal venetian blinds.

3) Chic-blinds or roll up curtains made out of sliced bamboo sticks.

4) Roll up curtains made out of dried grass.

5) Roll up curtains made out of sweet-odour herbs or coir.

In vertical venetian blinds, the slats are hung vertically & slide horizontally. They have an inverted U shaped top rail, duly powder coated, & is made out of extruded MS sections. The blinds slide horizontally when the nylon thread, hanging at one end of the track, is pulled. The blinds can be rotated by pulling the beaded garland. This beaded garland operates the rotating gear mechanism installed in the top track. The blinds or slates are made of stiff polyester + cotton fabric and are 100mm wide. The cost is about Rs. 500/Sqm.

In horizontal venetian blinds, the slats are hung horizontally and can be folded vertically by pulling a nylon thread. The slats are normally made of aluminium and are powder coated. To achieve the needed light or vision effects, slats can be rotated. This is done by rotating an Acrylic rod or an SS rod hung at one end. This rod when rotated operates the gear mechanism located in top rail. The cost of these horizontal blinds is about Rs. 500/Sqm.

In chic-blinds, bamboo sticks are sliced and are tied together suitably by two or more threads. The sticks are of about 2 mm thick. The curtains thus made have stiffeners at top and bottom end normally of timber-sticks. These can be rolled up by a pulling thread. Chic blinds prevent vision and sunlight and allow ventilation to a considerable extent.

Similar to Bamboo stick curtain, dried grass curtains are also made. Normally these curtains have a backing cloth. These are also of pulling up types. These days very attractive varieties are available in market.

Like bamboo and grass curtains coir curtains and herbal curtains are also available.

Lime plaster and cement plaster compared.

2012-04-20T14:45:00.002-07:00

Compare Lime plaster with cement plaster.

Sr. No.	Lime plaster	Cement plaster.
1	For plastering with lime, the lime used must be tempered and kneaded well.	Cement is ready for use and there are no preparatory steps
2	The ratio of lime to sand is 1 : 2 or 3.	The cement to sand ratio is 1 : 3 for high strength and 1 : 4 or 6 for normal walls.
3	The mixture prepared must be used within 4 hours.	The mixture prepared must be used in 30 minutes.
4	Lime plaster does not need watering/curing.	The cement plaster needs to be watered for 3 weeks for adequate curing.
5	The atmospheric carbon-di-oxide hardens or settles lime plaster.	The sprinkled water, working as a catalyst, hardens cement plaster due to formation of various silicates and aluminates.
6	The lime plaster is not as strong as cement plaster.	Cement plaster is stronger than lime plaster.
7	Durability of lime plaster is lesser than cement plaster.	Cement plaster is more durable than lime plaster.
8	The thickness of the plaster coat is 10 to 15 mm.	The thickness of the plaster varies from 7.5mm to 20mm.

What is terracotta?

2012-04-20T14:30:00.003-07:00

Explain the term terracotta. What are its properties?

Ans-:

Terra means earth and cotta means baked. Thus terracotta means baked earth. It is a type of earthenware or pottery made from local earth. It is also glazed from locally available galena. This glazing is not hard enough and can be scratched by knife.

The properties of terracotta are as under.

1. Terracotta is brittle.

2. Intricate items of terracotta can be moulded or shaped on potter-wheel.

3. It has a typical brownish red colour.

4. It is durable in exterior conditions and even in rains.

5. There are no atmospheric effects and lasts longer.

6. It can be scratched easily and is not very hard.

7. It can be either glazed or unglazed.

Why is Ceramic sink recommended in Laboratory platforms?

2012-04-20T14:20:00.005-07:00

Why is Ceramic sink recommended in Laboratory platforms?

Ans:

Ceramic sink is recommended in laboratory platform for…

1) Ceramic is not affected by strong acids and alkalies used in laboratory.

2) Stone sinks (granite) are also not affected by acids and alkalies. But stone sinks are difficult to clean especially at stone joints. And, in these joints the accumulation a dirt, moss etc, is a problem. Where as ceramic sink, due to rounded corners are easy to clean.

3) Even though ceramic sink is brittle, the laboratory apparatus that are cleaned in the sink, are normally made of glass. And in case there is an impact of one on another, the glass apparatus will break, & not the sink.

4) Steel sink is ruled out since strong acids react with steel.

5) FRP/Plastic sinks are ruled out since many acids & alkalies affect the plastic.

6) Glass sink will be acceptable but it is expensive.

Compare Venetian blinds with curtains.

2012-04-20T13:10:00.003-07:00

Compare Venetian blinds with curtains.

Ans.

Sr. No.	Venetian blinds	Curtains
1	Venetian blinds are made of slats/strips.	Curtains is made of cloth.
2	For horizontal blinds, the strips are normally Aluminium. Timber or plastic strips are also used in some cases. For vertical blinds, the strips normally are of cotton mix polyester yarn.	Cotton, polyester, silk, woollen, velvet are the normal types.
3	The strips fold on each other either vertically or horizontally depending upon whether vertical or horizontal	The curtains normally collect on one side, if single and both side, if split.
4.	The blinds are hung on the “C” shaped track in which they slide [vertical blinds] or towards which fold up [horizontal blinds].	The curtains are normally hung on a round pipe on which these slide to get collected.
5	To fold up, there are gears, pulling thread, tilting rod etc. Though operating blinds is simple, there exists a delicate mechanism.	To collect the curtain on one side, normally the hooks holding the curtain slide in the bar. This is achieved normally by simple push.
6	By tilting the blinds suitably, we can prevent the sunlight but can let in the diffracted light.	Such an arrangement is not possible in curtains.
7	Washing and cleaning is difficult.	Can be washed like a cloth is washed.
8	Since the operation is mechanised to some extent, a trained mechanic is needed for repairs.	Since there is no mechanism, simple repairs like ‘torn cloth stitching’ can be done easily.
9	Elongation or contraction of length is not a problem.	Cloth can elongate or contract depending upon the quality.
10	Horizontal venetian blinds do not have any acoustic control qualities. Vertical blinds may have some acoustic control qualities.	Cotton & woollen curtains have very good acoustic control qualities.

Major varieties of Indian Timber

2012-04-20T07:47:00.007-07:00

Enlist and briefly describe major varieties of Indian timber.

1. Deodar: Deodar is a conifer. It is light in weight. It is yellowish-whitish in colour and shows large knots. It is water resistant and also termite resistant. It is highly durable. It has a moderate strength. It is used for export packaging, false ceiling, panelling and light furniture.

2. Teak wood. Teak wood is a major timber used in India. It is deciduous/broad leaf tree. It is medium in weight. It has brown colour and close fibres. It is water resistant, termite resistant and is highly durable. It is strong and attractive. It is easy to work on since it possesses good machinability.

3. Sal wood. It is a broad-leaf tree. It is heavy in weight. It is durable but is not water resistance. It is not attached by white ants. Its colour is brown but cannot take polish well. It has a good machinability. It is used for door frames, ceiling frames, panelling frames, partition frames and other furniture which are to be painted.

4. Walnut. It is a broad leaf tree. It is moderately durable and moderately water resistant. It is moderate in weight. It has a brown colour, darker than teak. On polishing grain show food appearance. Its machinability is good and is easy to carve out.

5. Mahogany. It is a broad leaf tree. It is fairly strong and water resistant. It is red brown in colour with fine grains figure and it takes good polish. It is heavy in weight. Its machinability is good. Can be used to make all the furniture. The tree population in India is poor.

6. Sisoo. It is a broad leaf tree and heavy in weight. Its durability is good and, is strong. The colour is darker brown and is close grained. It has fair water resistance. Can be used to make most of the furniture. [It is called Shisam in North India.]

7. Rosewood. It is the most expensive timber in India. It is a broad leaf tree and very heavy in weight. It is highly durable, strong, tough and water resistance. It is not attached by termites. It has fairly good machinability. It has dark-gray/black grains with red/brown background. It takes high polish and is very attractive. It is used for expensive furniture of any kind and is very popular amongst Hindus for Mandir [Small temple in Home], since red colour is holy/pious to them.

There are some more varieties of timber that are used in India occasionally. These are

a] Ash, b] Silver oak, c] Aini, d] Babul, d] Mango, etc. Bamboo is also abundantly used for scaffolding and laddering. Bamboo, since it is an endogenous tree, is normally not covered as Timber. Cane, another endogenous tree, is also used for making chairs, sofas, beds and racks.

Can sea sand/salty sand be used for construction?

2012-04-19T20:47:00.002-07:00

Justify : Salt free sand should be used for mortar and concrete.

ANS:

Salts and alkalies play a damaging role in cement setting. Their presence affects the strength of the cement set.

In addition, salts & alkalies have hygroscopic properties. They absorb water from atmosphere and make the walls damp resulting into unhealthy atmosphere and weaker structure. Also, when the moisture in the wall evaporates, they leave behind white or gray spots spoiling the appearance of the building. This effect is called ‘Efflorescence effect’.

In case a situation warrants one to use sea sand only, it can be used by washing this with pure water till the sand is free from salt.

Hence salt free sand should be used for cement screed, mortar, plaster and concrete.

Methods of polishing timber

2012-04-19T18:31:00.001-07:00

Following are the ways of conventional varnishing/polishing timber......

1] Oil varnish: Here the resin is copal, a very hard gum, dissolved in a self drying oil like linseed oil. A thinner like benzene or turpentine may be present. This varnish is slow in drying [may be 24 hours or more] but forms a very hard film and is durable in exterior conditions. Repeated coats, over a period of time, of this varnish make the wood darker towards black-brown colour. This was the varnish used in earlier days in India and is still used in Indian villages to protect the wooden trusses, beams, doors, bullock-carts etc.

2] Turpentine varnish: This is prepared by dissolving soft gums like Rosin in pure turpentine. Since it dries quickly, a separate drier may not be needed. However, it does not withstand exterior conditions and hence can be used in interior only.

3] Water varnish: This is prepared by dissolving Lac in hot water along with Ammonia, borax and potash. This varnish is water resistance on drying and was used in earlier days for laminations on paper.

4] Spirit polish or French polish: Here the solvent is methyl alcohol and the resin is shellac or lac. These are quick in drying and the film is adequately hard. It has a bright and glossy finish. In India, we use this polish for all the furniture. This polish can be stained with suitable pigments to attain desired colour. French polish cannot withstand erosion due to direct contact of water. The process of application of this polish is explained later.

5] Lacquer polish: This polish was in use in India and other Asian countries till 1950. But, due to its toxicity, it is becoming obsolete. Shellac, which is a purified extract of lac, is coated on the furniture with or without a soluble oil. Another accepted version of lacquer-polish is by coating some polymer compounds dissolved in nitrocellulose. The lacquer-polish forms a strong, tough and transparent film on the surface. The film is resistant to water. With the advent of Melamine polish, which is much less toxic than this, this polish is not in use since last 50 years.

6] Melamine polish: Melamine polish is a synthetic resin and hardens when exposed to air. However this hardening is very slow and additional hardeners are added before spraying the coat of this polish. These hardeners, contained in a small bottle, are supplied along with the polish can. Melamine polish is water resistant. It has a better scratch resistance when compared to polishes explained earlier. It is available in mat, semi-gloss and gloss finishes. It is transparent but a faint brown tint is developed. The process of application of this polish is explained later.

7] Polyurethane coat [PU coat]:

A polyurethane, commonly abbreviated PU, is any polymer consisting of a chain of organic units joined by urethane (carbamate). The polish-coat of this forms a very strong, protective and glossy film on the wooden surface. Unlike melamine, the drying time for this coat is very short and is around 15 to 30 minutes. This coat is water resistant to a large degree. This polish is more expensive than even melamine polish and costs around Rs. 1200 per Sqm. The process of applying this polish is similar to that of melamine, except for the drying time, and hence is not explained in this chapter later .

Of these 7 processes briefed above, French polish, melamine polish and polyuretane coat are widely adopted practices in India.

What is an ELCB?

2012-04-19T17:45:00.001-07:00

Explain the function of an ELCB with neat sketch

Ans:

Earth Leakage Circuit Breaker or ELCB:

In case of earth leakage either through human body or through poor insulation of the instrument, the current may leak to the earth. That current is sensed through the help of electronic circuit that operates a relay. This relay disconnects the supply from the load. Hence the danger of shock is avoided.

Whenever there is no leakage to the earth, the current in phase wire and neutral wire will be equal. If there is a leakage to the earth, the current in neutral wire will be less compared to the phase wire. The electronic circuit detects this current difference and this sensor disconnects the supply.

3-Phase supply, Earthing wire & Neutral wire

2012-04-19T12:56:00.004-07:00

Explain terms: 1. 3phase supply

2. Earthing wire

3. Neutral wire

ANS:

1. Three phase electric supply:

In a normal single-phase line, there will be two wires. One is called as live wire or phase wire and the other is called as neutral wire. Voltage is available at live wire only. Neutral wire is used for completing the loop. In a three-phase line, there are three live wires and one neutral wire. [For star connection only].

The generator or alternator generates the electric current. In the electric generator, if one coil is rotated in the magnetic field, single phase or single supply of electric current will be generated. Whereas, if three coils separated 120° apart, are rotated; three separate supplies of electric currents are generated. Such kind of supply is called a three-phase supply. As a convention, for three phases, three basic colours, that is, Red, Yellow and blue wires are used. For neutral wire black colour is used.

2. Earthing wire:

In addition to phase wires and neutral wires there is one more wire [normally green] called earthing wire. This wire connects the device-body to the earth. This connection enables a large quantity of the leakage current to pass through this wire to the earth. And a very small amount of current passes through the human body to the earth. Thus, the human beings are saved from the shock effects.

3. Neutral wire:

In an alternative current for a single-phase supply, these are two wires. One is called as phase wire and other is called as neutral wire. Electric supply is given to the phase wire and the neutral wire just completes the circuit. The on- off switch is installed in phase wire. The neutral wire is normally black in colour.

Advantages of a multi strand wire over a single strand wire

2012-04-18T21:19:00.001-07:00

What are the advantages of a multi strand wire over a single strand wire?

Ans:

1) The multi strand wires are flexible and can be conveniently pulled through conduit and there is a less possibility of these getting ruptured during pulling. Single strand wires are less flexible and may get ruptured during this process.

2) Electrical fixture like holder, plug etc. hold the wire by a simple flat bottom fine thread straight shank screw. This fitment is better with multi strand wire. In a single wire, if the singular wire slips, the connectivity hampered.

3) Through the wire from control switch to the point or to electrical device should be continuous, there are some occasions on which wires need to be connected / joined. During such situation, for a multi strand wire, individual strand can be looped /connected to each other and a better joint obtained.

What do you mean by a 'Fuse"?

2012-04-18T21:12:00.000-07:00

What is the function of a fuse? And what are the types?

Ans: A fuse is a device that disconnects the circuit, in case the current exceeds the rated capacity of the circuit. If the circuit the circuit is not disconnected, either the instrument may get damaged or the wire may get heated up resulting into fire hazard or even the source may get damaged. Fuse basically consists of a piece of wire having lower melting point and is connected in series in the circuit. In case of short circuit, the fuse element gets melted and thus the electric circuit is broken.

The fuses are of two types 1] Rewirable fuse 2] Cartridge fuse.

Rewirable fuses were used earlier for electrical circuits of residential or commercial or industrial electrification. Whereas cartridge fuses are used in machinery. In case the fuse gets melted due to higher current/voltage, care should be taken to ensure that the replaced fuse wire/cartridge is of the same capacity. Else the fuse may not melt may not protect the circuit/appliance.

Compare MCB with fuse

2012-04-18T19:46:00.001-07:00

Compare MCB and fuse

	MCB (Miniature Circuit Breakers)	FUSE
1	MCB trips off in case of excessive load.	Fuse melts/fuses in case of excessive load.
2	MCB is to be just put-on after correcting the fault in wiring.	Fuse needs to be replaced with a new one.
3	Since we do not change the MCB, there is no risk of putting on the MCB/switch even if the fault is not correctly repaired.	There is a risk of putting on the switch in case; due to ignorance higher capacity fuse-wire is positioned.
4	Compact, small equipment.	Porcelain base and top. Not attractive.
5	Works on Bi-metal expansion or induced magnetism.	Works on melting/fusing due to high temperature.
6	Relatively costlier than fuse.	Relatively cheaper than MCB.

What are the short-comings of Plastics?

2012-04-18T13:48:00.002-07:00

SHORTCOMINGS OF PLASTIC

Though the plastics have found a wider application range, plastics do have some shortcomings. These are….

1. Lower Melting point and low heat resistance: Most of the plastics have low melting point and, have low heat resistance. Due to this, hot liquids/hot foods cannot be stored. Also plastic articles are needed to be protected form hot materials or fire.

2. Lower Hardness: The plastics are not that hard and have low scratch resistance.

3. Gradual disintegration: The plastics gradually disintegrate and become dull over a period of time. This disintegration is due to atmospheric effects of sun, rain, wind and temperature variations. Due to this disintegration, the luster of surface finish is lost and the article looses its attractive appearance.

4. Creep: The plastics exhibit high creep. In other words, plastics deform due to frequent loads it sustains.

5. Thermal expansion: The coefficient of thermal expansion for plastics is high and due to this, moderate temperature variations will affect the size and shape of articles.

Plastic chair V/s wooden chair

2012-04-18T13:45:00.001-07:00

Compare the advantages and disadvantages Plastic chair with a wooden chair

ANS:

Sr. No.	Plastic chair	Wooden chair
1.	Light in weight.	Relatively much heavier.
2.	Much cheaper.	Relatively much costlier.
3.	Becomes dull in 2 to 3 years since plastic looses its luster.	Can be repainted or re-polished to bring back the luster.
4.	Plastics have a creep problem & it de-shapes.	Wood does not have creep problem to that extent.
5.	Normally a ‘one piece molding’.	Assembled with various members.
6.	Relatively weak in load bearing capacity.	Much stronger in load bearing.
7.	Stacking facility for plastic chairs is usual or normal.	Stacking facility is not usual or normal.
8.	Does not catch fire.	Can catch fire.

FRP sheet roof V/s AC sheet roof

2012-04-18T13:37:00.002-07:00

Compare the advantages and disadvantages of FRP roof with an A. C. sheet roof for a small terrace.

Ans.

Sr. No.	FRP Roof	A.C. Sheet Roof
1.	Can be made elegant / attractive since various colors & designs are available	Has limitations on making it attractive since it can be painted only.
2.	It is translucent	It is opaque.
3.	Makes larger noise when rain-drops fall.	Relatively less noise during rains.
4.	It is not brittle and does not break easily.	It is brittle and can break even during careless handling.
5.	Can bend across the flutes & curved ceiling possible.	Can not bend.
6.	Cannot catch fire, but due to proximity of fire, it will melt or Char (M. P. 80º C ]	Totally fire proof, may crack at higher temperature.
7.	Can become dull or loose luster over a period of time – say 3 to 5 years.	No deteriorations due to atmospheric effect, but becomes weak when wet.
8.	FRP sheets are expensive compared to AC sheet	Much cheaper than FRP sheets.

Materials used for Thermal insulation

2012-04-18T13:12:00.002-07:00

List and explain in brief the materials used for Thermal insulation

1. Hollow bricks -

Walls made in hollow bricks are very good heat insulators. Hollow bricks could be of Burnt-Brick type or Concrete blocks. Air is a bad conductor of heat and these cavities retard the heat transfer through the wall. Porous bricks also have same properties.

2. Light weight concrete -

Concretes having density less than 1920 Kg / m³are called Lightweight concretes. Normal concrete where crushed stone or Gravels are used have a density 2400 Kg / m^3.In lightweight concrete, instead of crushed Stones/Gravels, expanded blast furnace slag is used. This blast furnace slag has a very good compressive strength and the concrete works out to be adequately strong. Thus, the walls with this concrete are good thermal insulators.

3. Air entraining Concrete/ Mortar / Plaster

Air entraining Cement, if used in concrete, creates minute air bubble in the mixture and, these air cavities assist the insulation. The air entraining cement is made by adding organic agents like Vinsol resin or Darax to the Portland cement. Air entrained Mortars and Plasters are also used for mortaring and plastering the walls. The use of air entrained concrete in cold countries is a normal practice for thermal insulation.

4. Combination of light weight concrete & Air entrained Concrete –

For better results of heat insulation, a combination of these two concretes is also possible. However, the multiple loss of strength by using the two relatively weaker concretes has to be considered while designing RCC structure.

5. Cork –

Cork is made from the bark of cork-oak tree. The bark of tree is cleaned, sized, ground and then baked. While it is being baked, it oozes natural resin. This resin binds the powdered cork to form a slab/sheet when pressed or rolled. Cork is a very light material having Sp. gr. 0.25. It is porous and not affected by moisture. It is a good Sound insulator both for sound transfer and acoustic effects. It is an electric insulator and heat insulator for temperatures below 70^oC.

Cork sheets are available in market and can be used for panelling. These can be coated with melamine polish to reduce abrasion damages, but the acoustic control is marginally affected.

6. Eel grass tiles:

Eel grass is used for making ceiling or panelling tiles. These tiles are used for both Thermal and sound insulation. Eel grass is a marine plant containing silica and iodine. Silica imparts the property of non-inflammability & iodine makes it termite proof. The grass obviously is a fibrous structure.

These tiles are very light in weight. These are specially recommended for acoustic control and thermal insulation. These have poor abrasion resistance. Hence the use may be restricted to ceiling and panelling above 2.4 meter heights.

7. Quilt -

Quilt is normally referred to some padded material like cotton pad stitched in linen cloth for bed covering or body covering. This cotton quilt can be a good heat & sound insulators. However, it is not moisture & termite proof.

For heat and sound insulation, a material called ‘Cobalt Quilt’ is used. This is created by stitching treated ‘Eel’ grass between very tough craft papers or canvas sheets. Eel grass is a marine plant containing silica and iodine. Silica imparts the property of non-inflammability & iodine makes it termite proof. The grass obviously is a fibrous structure.

8. Rock wool -

Rock wool or mineral wool is produced from flint stone, a calcareous stone. The stone is melted in a furnace at 1700^o C. This molten stone while it is leaving the furnace is acted upon by a blast of steam. This blast of steam converts molten mass into beads while getting solidified. These beads, still in hot condition are pressed to convert these into boards or blankets.

Rock wool is soft, light & flexible but has some resilient properties. It is available in markets as boards, blankets or quilts. This is used for thermal insulation.

9. Glass wool or Fibre glass

It is made from molten silica glass by forcing the same through apertures under steam or air pressure. A thread like mass is obtained and is known as Fibreglass or Glass wool.

It is fibrous in structure and has a good tensile strength. It is durable. It is a good thermal insulator and is abundantly used for thermally insulated partitions and panelling. It is also a good sound insulator from sound transfer point of view.

These are available in market in blankets form, but the blankets are not firmly built. And the blankets get de-shaped to bulk if not handled properly. Also, if these blankets or the bulk is handled with bare hands, the skin will irritate. Hence, use of hand-gloves is a must while handling these.

10. Coir

Coir is a hairy substance grown on Palm trees either on the fruit or on the trunk or under the leaves. This fibrous part is cleaned and used. Coir does not perish or degenerate under normal circumstance or in moist conditions and lasts long. Coir is a good thermal and sound insulator. Coir curtains and coir mats are insulating materials used by people under low income group. Coir quilts were also used earlier for padding and cushioning sofa.

11. Woollen carpets

Woollen carpets are a very good alternative for treating floor for thermal and sound insulation. For acoustic effects, it is the best. Natural wool is best but synthetic wool also give satisfactory results. It is normally backed by the jute cloth and is laid with an under-layer of PU foam or coir foam or some other synthetic foam. The jute backing cloth and the under-layer, both increase the insulation effect. Cleaning of these carpets is a bit tedious and vacuum cleaner is a must. Removal of stains is more difficult and Petrol-dry-washing agencies need to be called.

Woollen carpets are available in the market with varying thicknesses ranging from 8mm to 25 mm. The under-layers are of thickness from 12 mm to 25mm. These carpets are available in roll form of about 1.5m or 1.8m. Both the under-layer and the carpet are laid on the floor with intermittent use of rubber adhesive. The edges of the roll need to be hand-stitched for necessary width adjustments.

12. PVC carpets.

PVC carpets are good thermal insulators. These are fairly good sound insulators from sound transfer point of view but, for acoustic effects do not play a significant role. These are good electrical insulators.

The thickness available is from 0.6mm to 3mm. 1.5 mm or 2mm thick PVC, is normally used for flooring. These are available either in tile form or in roll form. The tile sizes vary from 250mm x 250mm till 450mm x 450mm. The roles have widths varying from 1.2m to 1.8m. These are pasted to floor with rubber adhesive. These can be pasted on smooth surfaces and not on rough surfaces like that of ‘rough Shahabad’. These can be easily cleaned by wiping with wet cloth.

13. Wooden flooring.

Wooden flooring done in natural timber is a good thermal insulator and fairly good sound insulator. Wooden flooring done in artificial timber like laminated particle/fibre board; does have thermal insulation properties but their sound insulation properties have some limitations. Wooden flooring are normally used for thermal insulation purpose or for places like dance floor, badminton hall etc.

Wooden flooring has a longer life than PVC flooring but can catch fire. The artificial timber floor is easy to clean with a damp cloth. The natural timber floor, if polished, cannot be cleaned with a damp cloth.

14. Thermocole, Polyurethane foam, Polyurethane beads etc.

Thermocole is a type of plastic and has good thermal insulation properties. It is available in sheet form up to 50mm thickness. It can also be molded to any desired shape in Plastic molding machine. Thermocole is used for sealing gaps in refrigeration chambers or for storing chilled articles. Thermocole tiles are used in false ceiling either as face tiles or as backing tiles. Thermocole is very light and is not adequately strong. It gets abraded with slight friction. Hence for thermally insulated partitions, it is only a filling material and not a surface material. Thermocole has moderate sound insulation properties.

Like Thermocole, PU foam or PU beads are also very good thermal and sound insulators. But these are expensive and are used in expensive refrigeration machinery. In interior jobs, where large quantity is required, Thermocole finds a better alternative.

15. Asbestos Cement sheet [A. C. sheet]

Asbestos is a natural mineral available in fibrous form. It is composed of silicates of calcium and magnesium [CaSiO3. 3MgSiO3]. This is mixed in cement and AC products are made. These products include pipes, plain AC sheets, corrugated AC sheets etc. AC sheets are good thermal insulators, but these are brittle. However, these find use in ovens etc. Also corrugated AC sheet roofing in factories, godowns and terraces/balconies is a better alternative from preventing radiated heat.

More information about this is given in chapter on Plastics.

16. Porcelain.

This is a clay product. It is a very good Electrical and Thermal insulator. It can withstand high temperatures. It is used for making Fuse boxes, High tension line holders.

17. Jute.

This is a vegetable fibre and is produced from ‘Jute plant’. The colour of the fibre varies from white to dark brown. It is bio-degradable. It is extracted from the stem of the plant after soaking it in the running water. The running water loosens the fibre and drives away the non-fibrous vegetable matter. Jute has very low thermal conductivity, it is electric insulator and is a very good sound insulator. Jute carpets, Jute curtains, Jute packaging and covering hot water pipes with Jute threads are Insulation applications.

Interior Materials

Compare ‘POP ceiling’ with ‘Suspended Al T ceiling or modular ceiling’.

Explain seasoning of timber.

What are the advantages of pre-cast slabs over slabs cast on site?

Teak wood window compared with MS window

Wooden staircase V/s RCC staircase

Advantages of a PVC carpet floor over woolen carpet floor

Carpet, rug and durry

Rubber Foam, U foam and Coir foam.

Window draping varieties

Lime plaster and cement plaster compared.

What is terracotta?

Why is Ceramic sink recommended in Laboratory platforms?

Compare Venetian blinds with curtains.

Major varieties of Indian Timber

Can sea sand/salty sand be used for construction?

Methods of polishing timber

What is an ELCB?

3-Phase supply, Earthing wire & Neutral wire

Advantages of a multi strand wire over a single strand wire

What do you mean by a 'Fuse"?

Compare MCB with fuse

MCB

(Miniature Circuit Breakers)

FUSE

What are the short-comings of Plastics?

Plastic chair V/s wooden chair

Compare the advantages and disadvantages Plastic chair with a wooden chair

FRP sheet roof V/s AC sheet roof

Compare the advantages and disadvantages of FRP roof with an A. C. sheet roof for a small terrace.

Materials used for Thermal insulation