What is Cement Plaster and Plastering:-
Cement Plaster is a layer of cement mortar of a desired proportion (mixture of sand and cement) as per specification. It is a thin layer applied over the rough masonry surface to make it smooth. For good plaster, it is essential that the plaster should have proper bond with the surface of masonry to be plastered.
Plastering is the process of applying plaster cover of cement mortar over the exposed surface in order to safeguard against penetration of rain water and other atmospheric agencies.
Advantages of Plastering:-
- Plastering also provides a finished surface over the masonry that is firm and smooth.
- It enhances the appearance of the building.
- Plaster safeguard against penetration of rain water and other atmospheric agencies.
- It acts as a damp-proof coat over the brick masonry work.
- Plastering helps to cover the defective workmanship in masonry, to conceal porous materials, and to provide a suitable surface for painting/whitewashing.
Disadvantages of Plastering:-
- The appearance of brick masonry such as Ashlar bond, English bond is not visible if plastering is done over such type of brick masonry.
Codes and Specifications used for the Plastering Work :-
1. Indian Standard Codes (BIS codes) :-
- IS 383 (Specification for coarse and fine aggregates for natural sources for concrete.)
- IS 1542 (Specifications for sand for plaster)
- IS 2645 (Specifications for integral cement waterproofing compound)
- IS 8112 (Specification for 43 grade OPC)
- IS 269 (Specification for 33 grade OPC)
- IS 1489 (Specification for Portland Pozzolana Cement)
2. American Standards:- ASTM C926 (Standard Specification for Application of Portland Cement-Based Plaster).
3. New Zealand Standards:- NZS 4251-1 (2007): (Solid plastering – Cement plasters for walls, ceilings and soffits).
4. European Standards :-BS EN 998-1 (Specification for mortar for masonry – Part 1: Rendering and plastering mortar).
Plastering Work Procedure:-
1. Preparation of Surface for Plastering:-
- All the mortar joints of wall should be rough, so as to give a good bonding to hold plaster.
- Clean all the joints and surfaces of the wall by brushing or scrapping with a wire brush. There should be not be any oil, grease and efflorescence spots on the surface to be plastered.
- If there are any cavities or holes on the surface, or any loose inferior materials, then fill it in advance with appropriate specified material.
- If the surface is smooth or the wall to be plastered is old, then rake out the mortar joint to a depth of 12 mm – 20 mm for proper bonding of mortar with the surface.
- Wash the mortar joints and entire wall to be plastered, and keep it wet for at least 6 hours before applying cement plaster.
- If the projection on the wall surface is more than 12 mm, then knock it off, so as to obtain a uniform surface of wall. This will reduce the consumption of plaster.
2. Applying Under Coat or Base Coat
- For uniform thickness of plastering throughout the wall surface, dots on the wall should be fixed first at a distance of 2m horizontally and Vertically. A dot means patch of plaster of size 15 mm x 15 mm and having thickness of about 10 mm.
- With the help of Plumb bob verticality is checked and screeds are formed as per the required thickness in the 2mx2m patches formed.
(Sometimes a cement slury coat is applied on the wall surface for proper bonding between the surface).
Procedure for applying First coat or Base coat:-
- The ratio of cement and sand for first coat plaster varies from 1:3 to 1:6.
- In case of Brick masonry the thickness of first coat plaster is 12 mm and for concrete masonry this thickness varies from
9 to 15 mm. - First coat of plaster should be applied between the patches formed on wall surface. This is done by means of trowel. Level the surface by means of flat wooden floats and wooden straight edges.
- First coat should set but it should not to dry. Roughen it with a scratching tool to form a key to the second coat of plaster.
3. Applying Finishing Coat :-
- Before applying the second coat the first coat applied should be kept wet/damp.
- Finishing coat is a final coat of plaster to be applied for finishing the plaster. The thickness of second coat or finishing coat may vary between 2 to 3 mm of cement mortar ratio 1:4 to 1:6.
- The finishing coat should be applied starting from top to bottom and completed in one operation to eliminate joining marks.
4. Curing of Plastering :-
- After both coats of plastering, it is kept wet by sprinkling water for at least 7 days in order to develop strength and hardness.
- Improper curing may lead to cracks formation or efflorescence in plaster work. Gunny bags can be used for keping the surface damp, to achieve proper curing.
Points to remember after Completion of Plaster Work
- Cleaning of door and window frame and floor area after completion of work.
- Curing should be started as soon as the plaster has hardened. Plaster should be cured for at least 7 days.
- Curing shall commence, 24 hours after the plaster is laid.
Plastering techniques and Machines:-
One of the most important and perhaps time-consuming jobs is plaster and mortar application for any building construction. It is the foundation of every building and is essential in structural integrity. Since plaster application ranges from exterior walls, interior walls, ceilings, and almost every area, for providing a smooth finished surface, it can certainly take up a lot of time and resources. Presently wall plastering is being done manually in most of the part of world i.e. the procedure of wall plastering with the help of masons and labors, which makes the process lengthy.
Objectives of Using a machine for Plastering:-
As compared to old plastering technique / Traditional plastering technique, following objectives can be achieved using machine for plastering.
- This Machine will reduce the human work reducing the labor cost. (Since labor employment is necessary for any country, this factor can be only considered in some exceptional cases.) Although skilled labor is required for operation of machines.
- It will avoid wastage’s of the mortar, thus saves the overall cost of construction.
- Higher accuracy of the plaster can be acquired along with fast plaster coverage.
- Machine is portable i.e. can be moved from one place to another.
- Cost of Plastering per Sq.m can be reduced for large construction work.
Types of plastering machines:-
- Spray plastering Machines
- Automatic Rendering machines.
Types of Spray Plastering Machines based on Pump used:-
Plaster sprayers are of three types:
- Worm-drive pump :- Most commonly, sprayers have a worm-drive pump that pumps the plaster up to a spray gun that has a large nozzle, usually 4 to 8 mm, that extrudes the plaster into a chamber on the end of the gun.
- Peristaltic pump: – There are a few plaster sprayers that have a peristaltic pump (a tube squeezed by rollers) which also requires compressed air to produce a spray. These types of plaster sprayer can also spray textured coatings with particle sizes up to about 3mm diameter, providing that they are not solvent based
- Piston pump: – Newer types of plaster sprayer have a piston pump, which has sufficient pressure to spray smooth (untextured) plaster without compressed air.
Advantages of Spray Plastering:-
- It is powerful and suitable for any type of surface.
- Can be sprayed to a long delivery distance and height.
- High output and less time consuming as compared to traditional method.
- These machines have long service life, if maintained properly.
- Less labor cost as compared to traditional method.
- Suitable for site mix with raw materials, alike traditional method.
- It can be used for a broad range of materials and application. (Ex- Putty spray, epoxy spray etc.)
Currently in construction market most widely presented plastering machines of German, Polish and Italian production: PFT, Putzmeister, Kaleta, Bunker, M-tec, Imer, Kappa etc. are available. In Indian market Lokpal Industries supplies various machineries. When choosing a plastering machine, one need pay attention on the performance, which is indicated in m3 or liters (per hour). For example, Productivity of the machine is calculated in terms of m3/h.
Plastering machine can be supplied plaster over considerable distances (20 meters or more), both
Horizontally and vertically, it all depends on the power unit, the fluid density and the length of the hose. It may cost around 30000 to 50000.
Automatic Rendering Machine:-
With increasing technology, plastering machines are also developed further, now automatic plastering machines are patented. These machines are capable of plastering a wall with absolutely “No Mason”. Finishing and trowelling is done simultaneously with precise degree of accuracy and thickness of plaster needed. This is indeed a useful and new advance technology in construction sector. This types of machines are also known as “Plastering Robots”
TUPO automatic rendering machine is available in market.
Advantages of this type of Machines:-
- Save 70% labor cost.
- Increase productivity 10-15times.
- Capability of rendering below or above window openings.
- Stable function & easy operate.
- Easy to Maintain.
Features of Automatic rendering Machines:-
- Wall Plastering Machine can reach the very top of the roof.
- Large hopper can load about 120kg cement.
- Intelligent Wall Plastering Machine can make the wall smooth one time within 1 min.
- Two mini vibrators on the Machine can avoid hollowness of walls, ensured rendering quality and fully adhesive.
- Machine equipped with omni-directional wheels. You can move it anywhere easily.
- Good quality Panasonic PLC can judge the operation mode of different condition.
- Tupo used it special Power head which is researched and developed by itself to drill the accessories. Highly increase the manufacturing precision and decrease working error or tolerance of auto rendering machine.
- The working efficiency can be 450 m²/8h.