What is pointing?

• It is the art of finishing the mortar joints in exposed brick or stone masonry with suitable cement or lime mortar, in order to protect the joints from weather effects and also to improve the appearance of building structure.

• Often an entire wall, or even a whole structure, is pointed because defective points cannot easily be detected, and adjacent joints may also be in need of repair. The mortar is packed tightly in thin layers and tooled to a smooth, concave, finished surface.

Scope of pointing

• Maintaining the joints of the structures.

• Pointing being cheap can be adopted in places

of low rainfall.

• Where the natural beauty of materials, viz.,

stone blocks, bricks etc, is desired to be

exhibited.

• Gives resisting power to the bricks and stones

used in construction towards weather

conditions.

Method of pointing • All the mortar joints (on the masonry face required to be

pointed) are raked out by a special pointing tool to a depth of 15 to 20 mm, so as to provide an adequate key for the fresh mortar used for pointing.

• All the loose mortar and dust are removed by brushes

• The joints and wall surface are washed with clean water, and then kept wet for few hours.

• The joints so prepared, are filled with suitable mortar with a small trowel. The mortar is well pressed into the joints to form a close contact with the old interior mortar joints. All excess mortar sticking to the sides is scraped away.

• The finished pointing work is kept wet for about 3 days when lime mortar is used for pointing and for 10 days when cement mortar is used for pointing.

What is plastering? • Plastering is the process of covering rough walls and

uneven surfaces in the construction of houses and other structures with a plastic material, called plaster or mortar.

Objective of plastering • To provide an even, smooth, regular, clean and

durable finished surface with improved appearance.

• To preserve and protect the surface.

• To cover up the use of inferior quality and porous materials of the masonry work.

• To conceal defective workmanship.

Requirement of the good plaster

• It should be hard and durable.

• It should be possible to apply it during all weather conditions.

• It should adhere to the background and should remain adhered during all climatic changes.

• It should be cheap and economical.

• It should offer good insulation against sound and high resistance against fire.

• It should effectively check the entry or penetration of moisture from the surfaces.

Method of plastering (general)

• The plaster may be applied in one or more coats, but the thickness of a single coat should not exceed 12 mm.

• In the case of inferior or cheaper type of construction, the plaster may usually be one coat. For ordinary type of construction, the plaster is usually applied in two coats, whereas for superior type of works it is applied in three coats.

• The final setting coat should not be applied until the previous coat is almost dry.

• The previous surface should be scratched or roughened before applying the next coat of plaster.

• In plastering, the plaster mix is either applied by throwing it with great force against the walls or by pressing it on the surface.

Types of plasters • Lime plaster

Lime plaster is a mixture of calcium hydroxide and sand

(or other inert fillers) in 1: 1 ratio.

Carbon dioxide in the atmosphere causes the plaster to

set by transforming the calcium hydroxide into calcium

carbonate (limestone).

In order to improve building properties of lime plaster ,

gugal (a kind of fragrant gum) @ 1.6 kg/m3 of mortar , is

added when the mortar is being ground.

In order to improve adhesive and tensile properties of

lime mortar, sometimes, small quantities of chopped

hemp (i.e., vegetable fibres) @ 1kg/m3 are added to the

lime mortar.

The lime mortar thus prepared is usually kept for 2 days

before use.

• Cement plaster:

Cement and sand in required proportions ( 1:3 or 4) are first thoroughly mixed in dry conditions and then water is added to form a paste of required consistency.

Generally it is mixture sand, portland cement and water mixed in a suitable proportion.

This prepared mortar for plastering should be consumed within 30 minutes after the addition of water.

• Gypsum plaster (plaster of Paris)

Gypsum plaster, or plaster of Paris, is produced by heating gypsum to about 300 °F (150 °C).

2CaSO4·H2O + Heat → 2CaSO4·½H2O + H2O (released as steam)

When the dry plaster powder is mixed with water, it re-forms into gypsum. The setting of unmodified plaster starts about 10 minutes after mixing and is complete in about 45 minutes but not fully set for 72 hours.

• Water proof plaster of Mortar:

This mortar consists of 1 part of cement, 2 parts of sand and

pulverised alum @ 12 kg/m3 of sand. To this dry mix , the soap

water containing about 75 g of soft soap/L of water , is added to

obtain the waterproof mortar.

• Heat resistant plasters

It's purpose is to replace conventional gypsum plasters in cases

where the temperature can get too high for gypsum plaster to

stay on the wall.

Heat resistant plaster should be used in cases where the wall is

likely to exceed temperatures of 50°C .

Heat resistant plaster is a building material used for coating

walls and chimney breasts.

Defects in plastering The following defects may arise in the plaster work:

Blistering of plastered surface: This is the formation of small patches of plaster swelling out beyond the plastered surface, arising out of late slaking of lime particles in the plaster.

Cracking: it is the formation of cracks in the plaster work due to the following reasons:

Structural defects in building

Movements in the background due to its thermal expansion or rapid drying

Movements in the plaster surface itself, either due to expansion or shrinkage.

• Efflorescence: It is the whitish crystalline substance which

appears on the surface due to presence of salts in plaster

making materials. It affects the adhesion of paint with wall

surface. Efflorescence can be removed to some extent by

dry brushing and washing the surface repeatedly.

• Flaking: It is the formation of very loose mass of plastered

surface, due to poor bond between successive coats.

• Peeling: It is the complete dislocation of some portion of

plastered surface, resulting in the formation of a patch. This

also results from imperfect bond.

• Popping: It is the formation of conical hole in the plastered

surface due to presence of some particles which expand on

setting.

Brick masonry

Brick masonry is built with bricks bonded

together with mortar. For temporary sheds mud

mortar may be used but for all permanent

buildings lime or cement mortars are used.

The various types of bonds generally used in

brick masonry are:

1. Stretcher bond

2. Header bond

3. English bond and

4. Flemish bond.

Stretcher bond • A stretcher is the longer face of the brick as seen

in the elevation. In the brick of size 190 mm ×

90 mm × 90 mm, 190 mm × 90 mm face is the

stretcher. In stretcher bond masonry all the

bricks are arranged in stretcher courses.

• However care

should be taken to

break vertical

joints. This type of

construction is

useful for the

construction half

brick thick

partition wall.

Header bond • A header is the shorter face of the brick as seen

in the elevation. In a standard brick it is 90 mm ×

90 mm face. In header bond brick masonry all

the bricks are arranged in the header courses as

shown in Fig. This type of bond is useful for the

construction of one brick thick walls.

English bond • In this alternate courses consist of headers and

stretchers. This is considered to be the strongest

bond. Hence it is commonly used bond for the

walls of all thicknesses. To break continuity of

vertical joints a brick is cut lengthwise into two

halves and used in the beginning and end of a wall

after first header. This is called queen closer.

Figure shows typical one brick and one and half

brick thick wall with English bond.

Flemish bond • In this type of bond each course comprises of alternate header

and stretcher figure. Alternate courses start with stretcher and

header. To break the vertical joints queen closers are required, if

a course starts with header. Every header is centrally supported on

the stretcher below it.

• Flemish bonds may be further classified as:

I. Double Flemish Bond

II. Single Flemish Bond.

• In case of double flemish bond, both faces of the wall have

flemish look, i.e. each course consist of alternate header and

stretcher, whereas single flemish bond outer faces of walls have

flemish look whereas inner faces have look of English bond [Fig

(a), (b)].

• Construction of flemish bond needs greater skill. It gives more

pleasing appearance. But it is not as strong as English bond. If

only pointing is to be used for finished wall, flemish bond may be

used to get good aesthetic view. If plastering is going to be used, it

is better to use English bond.

Advantages and Disadvantages of Brick Masonry Over Stone Masonry Advantages:

1. Since shape and size of bricks are uniform, it do not need skilled labour

for the construction.

2. Bricks are light in weight and hence handling them is easy.

3. Bricks are easily available around cities and their transportation cost is

less because their weight is less. Stones are to be brought from quarries

which are located only at few places.

4. It is possible to use all types of mortar in brick masonry. For

unimportant buildings even mud mortar can be used.

5. Thinner walls can be constructed with bricks but it is not so with stones.

6. It is easy to form openings for doors and windows.

7. Dead load of brick masonry is less.

8. In brick masonry mortar joints are thin and hence construction cost is

reduced considerably.

9. Brick masonry has better fire and weather resistance compared to

stone masonry.

Disadvantages:

1. Strength of brick masonry is less than that of stone masonry.

2. Durability of brick masonry is less.

3. Brick masonry needs plastering and plastered surface needs

colour washing. Stone masonry don’t need them and hence

maintenance cost is more in brick masonry.

4. Brick masonry absorbs water and there are possibility of

dampness. There is no such problem in stone masonry.

5. More architectural effects can be given in stone masonry

compared to that in brick masonry.

6. Stone masonry gives massive appearance and hence monumental

buildings are built in stone masonry.

Some points • Reinforcement masonry

does not require expensive element of concreting.

• Reinforcement masonry is capable of taking tensile and shear loads.

• Reinforcement masonry is a cheap, durable, fire proof and easy to construct.

• Reinforcement masonry is used for construction of walls, columns, lintels and slabs.

Important points • Concrete Association of India recommends face

thickness should be less than 5 cm and net area

should be minimum of 55 to 60% of the gross area.

• The holes in the block should be at least two in

number and they should preferably be oval shaped.

• The common sizes generally adopted for building

blocks are: 39x 19x 30 cm; 39x19x20 cm and

39x19x10 cm.

• The blocks are manufactured by using the mixture of

fine aggregates 60% and 6 to 12 mm size coarse

aggregate 40%. The fine modulus of the mixture

should range between 2.9 to 3.6. The 1:6 (cement to

combined aggregate) concrete mix should be used.

• The strength of block should be 30 kg/cm2

• For the construction of walls, only well dried blocks should be used. Blocks should have less than 10% water absorption for external walls and less than 15% for internal walls. Blocks with higher water absorption should be painted with water proof material.

• The joints should be 5 mm to 10 mm in thickness and cement, lime and sand mortar of 1:1: 10 should be used.

• When two walls of different heights meet each other, they should be separated by a joint.

• In order to avoid cracks , hollow blocks filled with concrete should be used at the junction of walls.

• When used in columns, the hollows within the blocks may be filled with concrete.

• Lintels should be made of hollow channel-shaped blocks filled with concrete having steel reinforcement at their bottom.

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