What Is Plastering?
Plastering is a method of applying a thin coat or covering of cement mortar on the surface of the brick masonry wall or concrete wall which is a mixture of lime or cement concrete and sand along with the required quantity of water.
Requirement of Good Plaster
- It must stick to wall and should remain adhered during all climatic changes.
- It must be cheap and economical.
- It must be hard and durable.
- It must provide easy to apply it during all weather conditions.
- It should prevent or restrict the entry or penetration of moisture from the surfaces.
- It must offer good workability.
The following table shows the plastering ratio with cement and sand quantity,
|Area (Sqm)||Plaster thickness (mm)||Mix Ratio of Mortar||Cement (in Kgs)||Sand (In cft)||Water (in Kgs)|
|10 Sqm||12 mm||1:3||49.37||3.77||44|
|10 Sqm||12 mm||1:4||39.29||3.99||44|
|10 Sqm||12 mm||1:5||32.54||4.14||44|
|10 Sqm||12 mm||1:6||27.80||4.24||44|
Wastage of mortar is not considered in the calculation. You can consider a wastage factor of 5% to the above calculation.
Calculating plastering quantity is a too difficult task. You just need to follow some simple steps to calculate plastering quantity. Plastering quantity includes the quantity of cement and sand required and the amount of water to be added to the mortar mix.
How to Calculate the Cement Sand Quantity for Plastering
Lets take one example,
Example: Suppose there is wall having following dimensions,
Length of wall = 10m
Height of wall = 3m
Area of Plastering Work = 10m x 3m = 30 m²
Plastering Thickness = 15 mm (0.015m)
Ratio of Cement : Sand = 1:4
First we calculate wet volume of plaster and then we will convert that in dry volume.
Wet Volume Plaster = Length of wall x Height of wall x Thickness of Plaster
= 10m x 3m x 0.015m
For, filling up joints and for uneven surface, 30 % more mortar is required.
Volume of wet mortar = 0.45 + (0.45 x (30/100))
= 0.45 + 0.135
= 0.585 m³
Now, to find out the dry volume of mortar, add extra 25% of wet volume.
Volume of dry mortar = 0.585 + (0.585 x (25/100))
= 0.73 m³
Proportion = 1:4 = 1+4 = 5
- Cement = (1/5) x 0.73 = 0.146 m³
Now, we know that cement 50 kg bag has volume of 0.035 m³.
By using above relation, we will find out number of bags from volume of cement.
Nos. of cement bags = 0.146 m³/ 0.035 m³ = 4.17 bags.
Sand = (4/5) x 0.73 = 0.584 m³
Cement current market price on an average 300rs per bag.
Cost of cement =4.17 x 300 = Rs. 1251
Sand current market price Rs. 55 Per cubic meter.
Cost of Sand = 0.584 x 55 = Rs. 32.12
Read More: 14 Types of Brick Bond & Their Advantages
Brick Wall Plastering Process
Following steps are involves in plastering process,
1. Preparation for Surface
- In the Plastering process First check the brick wall surface and clean it from dust, oil mortar dropping, sticking of foreign matter, etc.
- Brick masonry or concrete joint shall be raked out at least 10 mm deep. These enlarged gaps shall be sealed by cement mortar mix with a chemical in the proportion of 2:5:15 (2 parts chemical + 5 part cement + 15 part sand) and metal. Also, properly seal the holes made in concrete for the sleeves, etc.
- Remove or cut down any projection or irregularities in the plumb line shall be corrected by chipping or leveling coat with the bonding agent.
- Increase moisture in the surface by applying water before the application of the bonding agent.
2. Preparation of Mortar
- Now, mix cement and sand taking required proportion like 1:4 (Cement: sand). Add a sufficient amount of quality of water is added for getting a cohesive mortar. Mixing of materials can be done manually or by using machine mixing.
|Particulars Bond||Bond Coat||First Coat 8-10 mm||Second Coat 10-12 mm|
|CEMENT||1 Part||Part (1 Bag of 50 kg)||Part (1 Bag of 50 kg)|
|Sand||Nil||4 Part (4 x 0.035 = 0.14 m3)||4 Part (4 x 0.035 = 0.14 m3)|
|Water||Nil||As required||As required|
3. Plastering Process
Now, actual plastering process is start.
- Seal Joint: Rack the joints between RCC members and masonry out at least 10mm deep. Seal this crack with cement mortar mix with a chemical in proportion 2:5:15 (2 parts chemical + 5 parts PP cement + 15 parts sand) and metal.
- After that mark the levelling dots @ 1-meter centre to centre both ways in plumb and line on the surface. References shall be taken from the topmost point of the building irrespective of the location of the actual plaster.
- Before starting plastering on the surface apply cement slurry mixed in 0.5 cement and 1 water proportion by a stirrer to obtain a lump-free consistent slurry. This cement slurry is applied on the surface by using a brush or spray pump as a Bonding coat.
- Take slurry shall be applied on limited are where mason can reach within 10 to 20 minutes. (i.e. before setting off the Bond Coat).
- The well-mixed cement mortar first coat (8 – 10 mm thick) shall be applied to the surface within 10 – 20 minutes after applying a bonding coat before it sets or dries. Applied mortar shall be properly leveled by using wooden floats, Aluminium hollow sections, etc. A rough finish is done.
- Proper curing is done by a sprinkling water manually after the first coat is applied.
- Apply a second coat on the next day having 10 – 12 mm thickness. Properly level and finish it with wooden floats, Aluminium hollow section, etc. Elevation design shall be properly marked and made properly in line, level, and depth uniformly. Mark the Window moldings and finish it well. Clean all finished grooves, cornices thoroughly from all deposits.
- At the end of the day mark the finished plaster level and show the proper cut line. Clean all mortar lying on the surface at the end of day work.
- After the Plastering process work is done, it shall be cured by applying or sprinkling water on the surface for at least 14 days.
Quality Control Plan for External Plastering Process
1) Washed Sand
a) Slit Content, b) Bulkage, c) Gradation.
a) Cement Manufacture testing reports, b) Outside test as per approved frequency.
a) Manufacture test report.
Additional Precautions in Plastering Process
- After plastering work over clean window corners and proper finishing.
- Prepare moulds for windows, dry balcony drops.
- Give sufficient slopes on window niches.
- Provide water spouts for decks, dry balconies, etc.
- The clean top surface of cornices and proper rounding in corners.
- Clean all left-out mortar inside the rooms, walls, and floors of the mortar.
It is essential to follow proper method of plastering process for good quality plaster work.
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