“Column Plastering in Building Construction – Procedure, Mix Ratio & Quality Checks”

 



Columns are key structural elements that transfer loads from slabs and beams to the foundation. For strength, durability, and architectural appearance, column plastering is carried out after proper curing of RCC works. This article explains the technical aspects, step-by-step procedure, and important quality checks of column plastering as per construction practices.

🔹 Purpose of Column Plastering

  • Protection – Provides a cover against weathering, ingress of moisture, and carbonation.
  • Repair – Covers honeycombing, surface voids, and shuttering marks on RCC columns.
  • Alignment – Maintains uniformity of column faces in line with beams and walls.
  • Finish – Ensures smooth, paint-ready surface for interiors and exteriors.

🔹 Technical Specifications (General Practice)

  1. Mix Proportion: Cement: Sand = 1:4 to 1:5 (as per IS 1661:1972)
  2. Plaster Thickness: 12–15 mm (should not exceed 20 mm in single coat)
  3. Sand: Clean, well-graded, passing through 4.75 mm sieve (IS 1542)
  4. Water-Cement Ratio: 0.45–0.50 (controlled to avoid shrinkage cracks)
  5. Surface Preparation: Column surface roughened and slurry coat applied (cement: water = 1:1)
  6. Curing: Minimum 7 days with potable water (as per IS 456:2000)

🔹 Step-by-Step Procedure for Column Plastering

1. Surface Preparation

  • Remove dust, laitance, and loose particles.
  • Hack column surface or apply bonding coat for adhesion.
  • Wet the surface before plastering to reduce suction.

2. Fixing Plaster Guides (Mullions)

  • Vertical strips of mortar are applied at ~1.5 m spacing.
  • These guides define the thickness and alignment of plaster.
  • Plumb bob and spirit level are used for verticality checks.

3. Application of Plaster

  • First Coat: 8–10 mm thick base coat applied with a trowel.
  • Levelling: Surface leveled using straight edge/Aluminium section.
  • Second Coat: 3–5 mm finishing coat for smoothness (if required).

4. Finishing

  • Surface finished with steel/wooden float as per requirement.
  • Sharp edges are rounded slightly to avoid cracks.

5. Curing

  • Continuous curing for 7 days using wet gunny bags or sprinkling.
  • Early curing prevents shrinkage cracks and improves strength.

🔹 Technical Quality Checks on Site

✔️ Verticality – Checked with plumb bob and spirit level.
✔️ Thickness – Maintained with gauge strips, measured with Vernier/Scale.
✔️ Mixing – Ensure uniform mixing of mortar, no segregation.
✔️ Adhesion – Bond test (tap test) after 24 hrs to check hollow sound.
✔️ Surface Finish – Smooth, free from cracks, honeycombs, or undulations.

🔹 Common Defects in Column Plastering

⚠️ Cracks – Due to poor curing, rich mix, or rapid drying.
⚠️ Hollow Plaster – Poor bonding or insufficient slurry coat.
⚠️ Uneven Finish – Improper leveling or unskilled workmanship.

🔹 Safety Points

  • Scaffolding or platforms must be stable.
  • Workers should use safety gloves and helmets.
  • Avoid standing on unstable supports like paint drums (as seen on sites).

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