Some vital tips for providing cement plaster on wall surface

Cement plastering is normally applied to provide perfect coating to the outside and inside surface of wall. Cement plaster is normally given in a single coat or double coat. Double coat plaster is suitable where thickness of plaster is retained in excess of 15 mm or when it is necessary to maintain a very fine finish. The method for double coat cement plaster involves the following 5 steps.

a. Step-1-Making the surface ready for plastering
b. Step-2-Ground work for plaster
c. Step-3-Providing first coat (or under coat or rendering coat)
d. Step-4-Providing second coat (or finishing coat or fine coat)

STEP-1 (MAKING THE SURFACE READY FOR PLASTERING)

1. Retain all the mortar joints of wall rough, in order to maintain a good bonding to retain plaster.
2. Use a wire brush to cleanse all the joints and surfaces of the wall with a wire brush, the wall surface does not contain any oil or grease etc. left on wall surface.
3. In case the surface is smooth or the plastering wall is old one, then extract the mortar joint to a depth of minimum 12 mm to provide a superior bonding to the plaster.
4. If the projection on the wall surface remains over 12 mm, then rub it out to maintain a smooth surface of wall. It will minimize the consumption of plaster.
5. For any cavities or holes on the surface, fill it with exact material beforehand.
6. Roughen the whole wall to be plastered.
7. Wash the mortar joints and whole wall to be plastered, and make it wet for minimum 6 hours prior to use cement plaster.

STEP-2 (GROUND WORK FOR PLASTER)

1. To maintain smooth thickness of plastering all through the wall surface, initially settle dots on the wall. A dot belongs to patch of plaster with size 15 mm * 15 mm and thickness of about 10 mm.
2. Initially, dots are set on the wall horizontally and then vertically at a spacing of about 2 meters coating the whole wall surface.
3. With the help of plumb-bob, examine the verticality of dots, one over the other.
4. Once the dots are set, the vertical strips of plaster alias screeds are arranged among the dots. These screeds function as the gauges for retaining smooth thickness of plastering to be used.

STEP-3 (PROVIDING FIRST COAT OR UNDER COAT OR RENDERING COAT)

1. For brick masonry the thickness of first coat plaster usually remains 12 mm and for concrete masonry this thickness differs from 9 to 15 mm.
2. The proportion of cement and sand for first coat plaster differs from 1:3 to 1:6.
3. By using a trowel, provide the first coat of plaster among the spaces developed with the screeds on the wall surface.
4. The surface should be leveled with flat wooden floats and wooden straight edges.
5. Once the leveling is finished, leave the first coat to set but not to dry and then roughen it by a scratching tool to develop a key to the second coat of plaster.

STEP-4 (PROVIDING SECOND COAT OR FINISHING COAT OR FINE COAT)

1. The thickness of second coat or finishing coat may differ from 2 to 3 mm.
2. The proportion of cement and sand for second coat plaster differs from 1:4 to 1:6.
3. Prior to provide the second coat, moist the first coat uniformly.
4. Provide the finishing coat with wooden floats to a perfect uniform surface and apply finishing touch with a steel trowel.
5. If possible, the finishing coat should be provided starting from top towards bottom and finished in one operation to remove joining marks.

As soon as the plastering work is completed, water should be sprinkled over it to keep moist for minimum 7 days to maintain strength and hardness.



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Published By
Rajib Dey
www.constructioncost.co
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Plaster of Paris In Construction – Uses and Benefits

Plaster of Paris (POP) is a elementary building material that is mainly applied for coating walls and ceilings as well as for making architectural designs. It comes as dry powder and gets solidified when used along with water and heat.

The following types of plaster of paris is mainly available :-

a. Plaster of paris (Gypsum)
b. Lime Plaster
c. Cement Plaster

POP is originated by incomplete calcination of gypsum or calcium sulfate at 100 – 190 degree C without any admixture. The setting time is 5 – 20 min.

Benefits of Plaster of Paris:

1. It is light in weight and long lasting.
2. It contains low thermal conductivity.
3. It has strong resistance capacity against fire and it is considered as a very good heat insulating material.
4. It does not shrink at the time of setting and as a result it does not form cracks at the time of heating or setting.
5. It develops a thick surface to withstand normal knocks once drying is completed.
6. It blends easily with water and disperses quickly and level.
7. It contains good adhesion on fibrous materials.
8. It provides a solid surface on which the colours are set.
9. It does not provide any chemical action on paint and does not produce alkali attack.
10. Plaster of Paris provides a elegant interior finish. Due to inclusion of gypsum in POP, there is lot of shine and smoothness.
11. It can be easily changed into any shape.

Drawbacks of Plaster of Paris:

1. Gypsum plaster is not recommended for exterior finish as it is dissolved in water to some extent.
2. It’s cost is high as compared to cement or cement lime plaster.
3. It cannot be applied in moist situations.
4. Skilled labor should be appointed for proper application and consequently huge labour cost is required for using plaster of Paris.



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Published By
Rajib Dey
www.constructioncost.co
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Derivation for quantity in CFT in 1 Bag Cement

On the basis of the capability of the cement to be set in the existence of water, cements used in construction are classified as either hydraulic or non-hydraulic (see hydraulic and non-hydraulic lime plaster).

It will be difficult for non-hydraulic cement, to be set in wet conditions or underwater; instead, it sets once it dries and reacts with carbon dioxide in the air. It is defiant to any chemical attack as soon as it is set.

Density of Cement = 1440kg/m3

For 1 m3 Cement needed is 1440 kg

1 Bag of Cement = 50 kg

For 1 m3 Cement needed = 1440/50 = 28.8 bags

We know, 1 m3 = 35.3147 CFT

Or, 28.8 bags = 35.3147 CFT

Or, 1 Bag = 35.3147/28.8 = 1.226 CFT

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Published By

Rajib Dey

www.constructioncost.co

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Difference Between Cement Plastering and Rendering

Plaster and render refer to mortar coatings which give a protection to blockwork. The coatings provided on interior walls are named plaster, whereas the coatings on outside walls are termed render.

The plaster and render is differentiated with the uniformity of the mortar. Render usually consists of more cement as compared to plaster so that it becomes weather resistant. It is its primary function. It’s essential to render a building if it is developed with landcrete or mud blocks as when these blocks are uncovered to water for prolonged period, these can be broadened as well as turned out to be soft and cracked.

All exterior walls must be protected with render. The sides of the building, which have to combat with the scorching weather, should be covered with a heavier mix. The primary role of the plaster is to create the inside walls smooth and easily washable as well as make it good looking and decorate (paint or wallpaper) over. Plaster or render contains cement, sand, water and occasionally lime is included with the mix. Sharp coarse sands are most suitable for render, but this type of sand can make the mortar complicated to function wall. The sand applied for plaster must be well graded and less coarse as compared to the sand applied for render.‪

Because of diverse locations of utilizations of plasterwork, the percentage of material component for plaster and render may differ. As for example:

(i) Cement plaster 

Undercoat- cement:lime:sand (by volume) = 1:4:16

Finishing coat – cement:lime:sand = 1:12:30

(ii) Cement render 

Undercoat- cement:lime:sand (by volume) = 1:2:6

Finishing coat – cement:lime:sand = 1:3:6

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Published By

Rajib Dey

www.constructioncost.co

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