What is Plastering
Plastering is a process of covering the rough surface of work done with mortar. Plastering can be done from different materials depending upon the need. Term rendering is commonly used when a very thin finishing code is applied.
Mortar, which is used for plastering, is a heterogeneous mixture of sand, cement, and water, mixed in a prescribed ratio to get the mortar of the required proportion in the masonry plastering.
- Cement out of many types such as Ordinary Portland Cement and PPC.
- Ensure cement to be used is not less than 90 days old.
- Sand should not contain any organic impurities and harmful chemicals that may affect the quality of plastering work.
- Gradation should be checked to control the workability, strength, and control over the shrinkage.
- The strength of plaster will be affected if there are more fines in the mix.
- Water is an essential ingredient to get a mix.
- Two main functions of water. It starts the process of hydration, and it provides workability to the mix, but if the quantity increases, it will affect the strength of plastering.
- Water should not contain any accelerating and regarding chemicals in it.
- Avoid the use of stagnant water.
- Plaster should be applied while the water is in the plastic state.
- Cement hydration causes the mix to be hardened.
Objective of Plastering
Plastering work is performed to achieve various objectives, namely;
- The most common reason is to protect the external surface from the penetration of rainwater and from other atmospheric conditions.
- It can give a smoother surface so that dirt and dust don’t clock on vertical surfaces.
- It can be applied to give a decorative effect.
- Various textures and shapes can be rendered on plaster.
- It can protect against insect penetration.
- To cover up the inferior quality of members of the masonry.
Consideration Before Plastering
The following points should be considered and planned for before any plasterwork begins.
- Types of surface plaster are to be applied so that necessary preparations before plastering can be minimized.
- Area type of finish on thickness required so that mixed design can be planned appropriately.
- Details of scaffolding to work in the correct sequence, particularly for ceiling and height work.
- Details of accessories to be fixed in plaster so that damages can be minimized.
- Type of decorative finish to be applied, if any, to understand compatibility with the base coat.
- It is a proven multipurpose material. It can be applied on brick walls, stone masonry walls, or RCC surfaces.
After drying, it produces a durable surface, which is easy to clean.
Plaster can be applied on flat or curved walls or ceilings, and it can be treated with painting wallpaper, white washings, stenciling.
Planning and Procedure of Plastering Design.
- Ensure that the concrete surface has been adequately cured.
- All fixings such as window sill, door and window frames, and pipes and conduits are correctly installed.
- Also, check for the plainness and dryness of the surface.
- Make sure to provide proper time between under and finish coats.
Sequence of operations
- For external plaster, start from the top and proceed downwards.
- Begin internal application after brickwork and the shuttering is completed.
- Arranged for a constant supply of plastering material.
- Ceiling work should be done first so that the scaffolding can be removed.
Precautions of Plastering Scaffolding
- Use double scaffolding as holes are later filled in an incorrect manner.
- Bamboo or bullies should be buried at least 45 centimeters in the ground.
- In short, plum holes in masonry for support should not be made at the skirting level.
- To avoid seepage or leakage in the wall from the holes,
- the distance between scaffolding and wall should be 900 millimeters.
- It should be removed from top to bottom.
- Ensure the platform can carry the weight of two people.
Preparation of the background
- The background should be prepared in a way that the strength of the plaster is achieved by proper bonding of motor with the background surface.
- Ensure cleanliness, roughness, and evenness of the background surface, along with the quality of mortar.
- Also, ensure that there is no discontinuity in the surface of the background.
Preparation of masonry surface
- Removed brick efflorescence or green algae by rubbing with a wire brush surfaces to be rendered must be clean and free from all dust, loose materials, etc
- Fill the side gaps in masonry and joints of the beam and wall with cement rich mortar of ratio 1: 3. It is very common to have leakages through these junctions.
- Masonry should be allowed to dry out before plastering work begins.
- All joints in the masonry should be raped out to a depth of at least 12 millimeters.
- Make mortar (levels)dots, then take the plumb bob from top to bottom at all the edges to ensure the level
- Confirming to horizontal and vertical lines will give properly finished surfaces.
- Keep the minimum thickness of the plaster if beam or column is bulged out than chiseling, should be done after RCC designers’ permission
- Fixed chicken mesh at all the reinforced cement concrete junctions
- Wet the surface is a day before plastering
- Check sizes, levels, and dimensions for all the door and windows for smooth opening
Preparation of Reinforced Cement Concrete surface
- Hacking It is a process of toughening the concrete surfaces.
- It is performed to ensure proper bonding of plaster on the reinforced cement concrete surface, which is usually smooth.
- Sand should confirm, the silt content should not be more than 7%, and the finest modelers be less than 1.5.
- The material should be measured using engaged boxes.
- Cement should be measured by weight.
- One cubic meter of dry hydrated lime gives approximately 0.85 cubic meters of lime putty.
- The quantity of water is about 70% of the weight of cement. This varies as per mortar design.
- Do not make a mortar mix of more than three bags, which is 150 kg in weight at a time, to avoid setting of mortar before consumption.
- Preferably mortar mix should be used within a half-hour of adding water.
- Do not pour excess water as it will cause cement slurry to flow.
- Keep the floor area clean where the mortar is mixed.
- Ensure that the dry mix of sand and cement is uniform in color.
- Keep the mortar mix agitated, turnover the mixture every 20 minutes.
- Any motor which has set or hardened should be rejected immediately.
- Mixing by machine is preferred
- precautions to be taken while applying the first coat. The first coat’s thickness of plaster is about 10 to 15 millimeters. The proportion can be 1 to 5. If it is a black coat, applied the plaster to the same face level and finished the same with a trowel’s help.
- Ensure that no uneven surfaces are left after the first coat application. Check the surfaces with string on respective dots to ensure levelness.
- Roughen the surfaces with wires for better bonding to the second coat thickness of the second coat. Plaster should be 6 to 8 millimeters in the proportion of one is 5.
- It should be applied on the third day or should be applied within five days from the first coat.
- Avoid using dry cement to minimize the cracks on the surface.
- Cut the plaster of the parapet wall from inside at 400 millimeters from the slab
- For provisions of waterproofing, leave 125 millimeters from the bottom of the floor for skirting.
- Curing is one of the most critical activities and should be carried out for a minimum of 15 days.
- Plaster is expensive to remove and redo
- The aesthetics of a building are dependent on the plaster surfaces.
- Ensure proper preparation procedures on precautions are r followed to get a beautiful appearance.
Types of Plaster Bonding.
Mechanical bonding: Mortar squeezes into the irregular surface and gets into the lock when it gets hardened.
Adhesive bonding: due to Portland’s adhesive properties, cement on hardening bonding mainly depends upon the surface’s roughness on which the plaster is to be applied and the quality of the mixed material.
Curing of Plastered Wall
When the plaster is done, it is to be cured by spraying water on the surface for a minimum of seven days.
Effect of Weather on Plaster
The critical effect on plasterwork is significant. Unless special precautions are adopted, plastering work shall be suspended.
The setting and hardening time increased with a reduction in temperatures. Accordingly, the work is to be programmed or reprogrammed.
The rainy season may impair the finished plasterwork by retard the drying out for periods of a week or a month
Dry weather conditions.
The coat will set rapidly and will have powdery surface results in not allowing the next coat is finishing coat to stick correctly.
In this condition, the surface should be kept wet during the curing period.
Different Types of Plaster Finishes
The common types of plaster finishes are
- Lime plaster.
- Cement plaster (smooth, mala, rough, pebbled, texture).
- Mud plaster and
- Stucco plaster
This is where lime is added to the cement. The proportion which is generally followed is one lime and one sand.
Nowadays, this type of plaster is not in use. Lime forms a light, clean, and durable surface that is resistant to weather and mold. When lime is mixed with water, it is called hydraulic lime.
This plaster is weak, soft, and takes a longer time to harden. Hydraulic lime should be used within two hours and should be remixed every 20 minutes. Lime plaster surface should not be finished very smoothly, as it will not allow the paint or whitewashed to stick on the surface.
The plastered surface should be kept wet for a minimum of seven days to prevent it from cracking.
Smooth Finish Cement Plaster.
It is usually done on internal faces and in a single coat of 12 millimeters thickness. There should not be any rendering applied on the base surface.
A mixture of hydraulic, lime, and cement slurry may be applied to get a smooth finish. No sponging is done to expose the sand grain.
It is used in internal walls, is similar to smooth plaster; however, the surfaces are kept rough.
No cement slurry is applied after plastering, which leaves behind small voids. This helps for better bidding of P O. P. And putty.
Sand Faced Plaster
Sand faced plaster is usually external plasters. The first coat of sand faced plaster is done in a 1-4 ratio, and after seven days of curing the second coat of ratio, 1-3 is applied.
Curing should be done for 15 days.
Rough plaster is said when the final finished surface is further sprinkled with sand. Two coats are applied. The first one is of 12 millimeters thickness, and the second coat is of 10 millimeters thick with a 1 to 3. To make bays more plastic, add 10% of hydrated lime that of cement mortar.
In earlier days, mud was used to smooth in the masonry wall. Mud mortar contains a mixture of clay grass and hemp. This is generally applied in two coats, and no curing is required in this type of plaster.
This is the cheapest type of plaster used mostly in rural areas.
Stucco plaster usually means an architectural coating for the outside of a building for an attractive appearance.
In this type, the first two coats are the regular coats of plaster, the third and your final coat is the finishing coat, which renders texture and gives a decorative appearance.
There are many types of stucco plaster:
Stone Crete Plaster
Stone Crete Plaster is composed of cement, crushed coarse aggregate. Usually, marble or granite chips find marble powder and water. White cement can be used instead of gray cement, depending upon the requirement.
This type of plaster provides the hardest decorative texture.
Exposed Aggregates/Pebble Plaster
In this type of plaster, the aggregates, which are available in different colors, are exposed on the surface. Stones should be six millimeters to 12.5 millimeters in size and are dashed against the surface so that they are stuck in position.
The proportion of the mortar should be 1:3
Granules mix plaster
Granules Plaster: dry Granules mixed with silica sand color pigments and pure acrylic polymer emulsions are applied.
Granules offer unique options for mono or multi-color shades and sizes.
Other Stucco Plasters
Texture finish is used in both interior and exterior sides of the building to provide a textured appearance.
Rollers with patterns and rough finishes are dispersed in inorganic mineral fillers and pigments and then rolled on the finished plastic coat.
When the two or more plaster coats are to be applied, the cause of sand should be mixed in the first coat, wherein single coat plaster the finest modules of sand should be 1.5 the strength of plaster mix will reduce if the finest modules of the sand are reduced.
Summary of Types of Plasters
Many types of plaster available offer a wide range of textures.
Plaster can be lime-based, cement-based acrylic, or cellulose; depending upon whether conditions finished required and local material availability, the plaster type should be picked.
Common Plastering Tools
Top tools used for plastering.
It is used for spreading the mortar on the surface of the fresh mortar. The wooden float has a wood blade, which is 4 to 5 inches wide and 10 inches long.
Aluminum Hollow Box Section
This is a versatile aluminum hollow section product available in various lengths and grades used to level the blaster and remove the undulant surface.
A hacking axe is used to provide the rough surface on RCC Member for plastering work.
A Plumb bob is a weight with a pointed tip on the bottom that is suspended from the string used to check the structure’s vertical alignment.
It is a flexible ruler and a standard measuring tool. Steel or invar tapes are commonly used to take measurements.
PVC Water Level Tube
This is used for measuring and comparing the level of the different structural members.
A trowel is used for moving some amount of viscous material and applying plaster.
Angle Tool (Corners)
Angle Tool is known as corners; these are steel plates spent at a 90-degree angle. It is used for finishing and ensuring horizontal or vertical edges are at right angles.
There are two types of tools available. One is an internal angle tool, and another is an external angle tool.
Hawk is used to carrying mortar while pointing or plastering. Mortar is removed with the help of travel and is available in wooden and steel.
The plastering trowel is made up of a steel plate. Having a size is about 275 millimeters by 125 millimeters. This is used for laying the mortar on the surface and for finishing to give a smooth surface.
The screen is used to see if sand on construction sites is appropriate for a particular use. Usually, 1.6 millimeters G I wire of whole size four by four millimeters. The safe cylinder is usually 500 millimeters in diameter and 1500 millimeters in length.
Sand Faced Machine
Sand faced machine is used on an external wall surface to get the sand-faced texture.
Measuring boxes are used to measure cement and sand volume to ensure correct proportions—boxes volume of 1.25 cubic feet 35 liters, which equals volume over cement bag.
The standard dimensions are 300 by 300 By 390 millimeters.
Wheelbarrows are used for material handling and carry capacity ranges from 24 to 65litres.
Maintenance of tools.
- Proper care should be taken of all the tools.
- All tools should be cleaned by scraping and washing at the end of each day.
- Cleanliness is essential as the contamination will affect the quality of work and affect performance and reduce the tools’ useful life.
Common Plaster Problems.
There are mainly four main reasons for plastered to crack spate or detach.
Reasons for Plaster Problems
Stresses due to overloading on walls, settlement of the building, vibrations, undersized beams, and flow choice will create cracks originating from random points.
Defects related to unwell, proportioned mix, incompatible base, finish coats, improper plaster applications, inadequate thickness, and improper chemicals, add mixtures.
Plaster needs to be cooled to reduce shrinkage; Cracks.
Plaster is vulnerable to water damage if the wall is continuously wet.
Common Plaster Problems
Blistering of Plastered Surface
Blistering is forming small patches of plaster swelling out beyond the blasted surface arising out of late slaking of line particles in the plaster.
The development of one or more fissures in the blasted surface is known as fracking, causing cracking.
Cracking is caused due to the perfect preparation of background discontinuity of surface movement in the background due to its thermal expansion or rapid drying. Other causes of cracking are movements in the plastic surface itself, either due to expansion or shrinkage.
A very thick coat of plastering will cause excessive shrinkage.
Faulty workmanship is also one cause of cracking.
Due to the presence of salts and construction material, white patches can be seen on the surface of the finished surface, known as efflorescence.
It will give a bad appearance and will also affect the bonding of paints. Efflorescence can be removed by washing the surface.
Repeatedly falling, which includes flaking and peeling, is one of the defects in plastering, bonding between succeeding coats with results in the formation of very loose mars on the plastered surfaces flaking.
Whereas the complete dislocation of some potion of plastered surface, which looks like patches, is called peeling
The Conical hole on the plastered face due to expanding particles after setting is called popping.
Rusted stains appear when the plaster is applied on the metal like chicken mesh to get a finished surface, the workmanship should be proper, or else an uneven surface will be seen.
When the blasted surface is exposed to dry conditions, fine cracks appear on the plaster’s surface in crazy patterns, having a length of six millimeters to 75 millimeters. This is called crazing.
Generally observed during the rainy season when the wet surface starts to dry, it will reduce your ability of the concrete structure it appears in 1 to 7 days or maybe later.
Rapid loss of moisture content will result in a decrease in volume and constant drying shrinkage.
It occurs when the water starts evaporating from the exposed surface of plaster. The moisture differential along the slab’s depth causes the stream to induce tension and results in drying shrinkage.
It is necessary to maintain the time interval to prevent drying shrinkage.
The second coat should be applied after shrinkage of the first coat ends, preferably provide time in developed 2 to 3 days in summer and four days in winter as the model’s setting will be rapid in summer and slower in winter.