Plaster Calculator

How to Use

Wall Plaster Formula & How It Works

Wall area  = 2×(L+W)×H
             − (doors × 1.8×2.1 m²)
             − (windows × 1.2×1.2 m²)

Wet volume  = Net area × Thickness
Dry volume  = Wet volume × 1.3 (dry factor)
              × (1 + wastage%)

For a 1:S mix (S = sand parts):
  Total parts = 1 + S

  Cement m³ = dry volume × (1 ÷ total parts)
  Cement kg  = Cement m³ × 1,440 kg/m³
  Cement bags = ⌈cement kg ÷ 50⌉

  Sand m³    = dry volume × (S ÷ total parts)
  Sand kg    = sand m³ × 1,600 kg/m³

Example Calculation for Wall Plaster

Plastering Tips for Bangladesh

• 1

  Wet the Brick Wall Thoroughly Before Plastering

  A dry brick surface absorbs water from the plaster mortar too quickly, preventing proper bonding and causing the plaster to crack within weeks. Sprinkle water on walls until they are damp but not dripping wet — a 'suction test' (water absorbed in 30–60 seconds) indicates the right dampness.

  Rule: surface should absorb water in 30–60 sec before applying plaster

• 2

  Apply Plaster in Two Coats for External Walls

  For external walls, apply a scratch coat (15 mm, 1:5 mix) first, allow it to set for 24 hours, score the surface, then apply a finish coat (5 mm, 1:4 mix). Single-coat external plaster is more prone to cracking and water penetration in Bangladesh's monsoon climate.

  External: scratch coat 15 mm + finish coat 5 mm = 20 mm total

• 3

  Use Waterproofing Compound in Wet Areas

  Add a waterproofing admixture (such as Fosroc Cebex or Sika waterproofer) to plaster mortar in bathrooms, kitchens, and external walls. It adds approximately BDT 3–5 per sqft but prevents damp penetration, efflorescence, and costly future repairs.

  Dosage: typically 200 mL per 50 kg cement bag (check product spec)

• 4

  Cure Plaster with Water for at Least 7 Days

  After application, keep the plaster moist by sprinkling water 2–3 times daily for a minimum of 7 days. Premature drying causes shrinkage cracks that are difficult to repair invisibly. In hot and windy weather (April–May in Bangladesh), increase curing to 10–14 days.

  Curing: 7 days minimum · 10–14 days in dry/hot weather

• 5

  Buy Sand from a Known Source

  Construction sand in Bangladesh varies significantly in quality. Coarse or salt-contaminated sand weakens the plaster and causes efflorescence. Use clean river sand (zone 2 or 3 grading). Always check for visible salt deposits or excessive clay content before purchase.

  Standard: zone 2–3 river sand · avoid sea/saline sand

• 6

  Order 10% Extra Cement — Measurement Errors Are Common

  On-site measurement and mixing are never perfectly accurate. Running out of cement mid-job and buying a new batch — even from the same brand — can result in visible colour variation in the finished plaster. Always order at least 10% more than the calculated quantity.

  Order qty = Calculated bags × 1.10 (round up to nearest bag)

Frequently Asked Questions

References & Standards for Wall Plaster

• ↗Bangladesh National Building Code (BNBC) 2020 — plaster thickness and mix specifications for internal and external wall finishes
• ↗Asian Paints Bangladesh — Standard of Good Practice for application of cement-sand mortar base plaster finishes
• ↗Bangladesh Schedule of Rates 2023–24 — plastering work quantities, mix ratios, and material allowances for government projects
• ↗NCC BCIF — plastering work measurement methodology for residential and commercial buildings

Material quantities are estimates. On-site consumption varies with surface texture, application method, and worker technique. Last reviewed: May 2026.