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Plastering

STEP BY STEP TO ACHIEVE A SMOOTH PLASTER WALL PLASTERING/ RENDERING SURFACE USING MIX RATIO.


 PLASTERING AND WALL FINISHES

Roles of plasterer

  1. Applies coats of plaster to interior walls, ceiling and partitions of building to produce finished surface, according to architects drawings or oral instruction, using hand tools and portable power tools.
  2. Directs workers to mix mortar to desired consistence and erect scaffolds.
  3. Spread plaster over masonry base, using trued and smoothens plaster with trued and float to attain uniform thickness. 
  4. Roughens undercoat with scratcher or trowel to provide bonds for succeeding coats of plaster.
  5. Creates decorative textures in finish coat by marking surface of coat with brush and trowel or by spattering surface with pebbles.
  6. Mix mortar with appropriate Cement mix ratio.
  7. Install gauge on surface of building to indicate thickness of plaster to be applied.
  8. Perform maintenance work.


PLASTER WALL: PLASTERING TOOLS AND EQUIPMENT


  •  Plastering Trowel– Made from stainless or carbon steel.
  • Plastering corner trowel produces a better corner edge to edge finish.
  • Hawk – A hand flat base from which plaster can been more easily applied.
  • Plastering float – A lightweight trowel to create a good coat finish.
  • Plaster mixing head pan or bucket.
  • Plaster board and drywall scarifier.
  • Straight edge – To check the finished surface is flat.
  • Spirit level for checking the finished surface level.
  • Dustsheet – To protect floors and furnishings.

   

Materials for Plaster wall Plastering and Rendering 

 The following materials are used for plaster wall Binding e.g. cement, lime, gypsum, water,Plastering sand, etc.


Background preparation 

Step 1 – Preparing of surface for plastering

Step 2 – Gauging

Step 3 – applying first coat (under coat or rendering coat)

Step 4 – applying second coat (finishing coat or fine coat)


Step 1

  •  Keep all mortar joint of wall rough, so as to give a good bonding to hold plaster.
  • Clean all the joints and surfaces of the walls with a wire brush. There could be no oil or grease etc. left on the wall surface.
  • Rake out the mortar joint to a depth of at least 12mm to give a better bonding to the plaster.
  • If the projection on the wall is more than 12mm, then knock it off, so as to obtain a uniform surface of wall. This will reduce the consumption of plaster.
  • Fill any existing cavities or holes on the surface.
  • Roughen the entire wall to be plastered.
  • Wash the mortar joints and entire wall to be plastered and keep it wet for at least 6 hrs. Before applying cement plaster.



Also read: How to calculate the amount of cement, sand and granite for a concrete mix


Step 2

  • Fix dots on the wall to get uniform thickness  of plastering throughout the wall surface, A dot means patch of plaster of size 15mm and having thickness of about 10mm.
  • Dots are fixed on the wall first horizontally and then vertically at the distance of 2 meters.
  • Check the vertical of dots, one over the other, by means of plumb-bob.
  • The vertical strips of plaster known as screeds are formed in between the dots. It serves as the gauges for maintaining even thickness of plastering being applied.


Step 3:

  • Incase of brick masonry, the thickness of first coat plaster is in general 12mm and concrete masonry, this thickness varies from 9 to 15mm.
  • The ratio of cement and sand for first coat plaster varies from 1:3 to 1:6
  • Apply the first coat of plaster between the spaces formed by the screeds on the wall surface. This is done by means of trowel.
  • Level the surface by means of flat wooden float and wooden straight edges.
  • After levelling, leave the first coat to set but not to dry and then roughen it with a scratching tool to form a key to the second coat of plaster.


Step 4

  • The thickness of second coat of finishing coat may vary between 2 to 3mm.
  • The ratio of cement and sand for second coat plaster varies from 1:4 to 1:6
  • Before applying the second coat, damp the first coat evenly.
  • Apply the finishing coat with wooden floats to a true "even" surface and using a steel trowel, give it a finishing touch.
  • As far as possible, the finishing coat should be applied starting from top towards bottom and completed in one operation to eliminate joining marks.
  • After completion of the plastering work, it is kept wet by sprinkling water for at least 7 days in order to develop strength and hardness.

Also read: How to calculate the amount of cement and sand for plaster wall


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