| Primary value | 12 mm (1 : 6 cement-sand mortar) |
| Applies to | Internal brick or block masonry walls · RCC walls and column / beam soffits (after surface preparation) · Standard residential and commercial construction |
| Exceptions | Ceiling plaster (smooth finish) → 6 mm @ 1:3 or 1:4 |
| Internal — over rough RCC surface → 12 + 6 mm two-coat (18 mm) | |
| Concealed-conduit walls → 12 mm + skim-coat punning | |
| Punning over plaster (gypsum / lime) → 2 – 3 mm | |
| Measured as | Net thickness of finished plaster between the wall surface and the painted face. Measured perpendicular to the wall — not on the diagonal. |
| Source | IS 1661 — Clause 5 ✓ Verified |
4 related items across IS codes, knowledge articles, design rules, maps and tools
12 mm internal plaster is the thinnest layer that hides typical brick joint variation (3–5 mm) without telegraphing the masonry pattern through the paint. Any thinner and small undulations show; thicker wastes cement and creates shrinkage cracks.
Indian apartment finishes: 12 mm 1:6 internal plaster + 2–3 mm gypsum punning + emulsion paint. Punning has replaced traditional double-coat 18 mm plaster in modern residential because gypsum gives a smoother substrate for paint.