AAC's flat, accurate faces make plastering easier than on brick — if the plaster is treated as a thin finish, not a levelling layer.
Before Plastering
- Wait at least about a week after the wall is complete.
- Fill joints and chips with AAC repair mortar.
- Fix mesh across junctions of AAC with columns and beams, overlapping each side by about 150 mm.
- Dampen the surface lightly so the porous block does not draw water out of the plaster too fast.
- Bonding coat or spatter dash for cement plaster.
Cement or Gypsum?
| Cement plaster | Gypsum plaster | |
|---|---|---|
| Use | Internal and external | Internal only |
| Thickness | 10 – 12 mm in, 15 – 20 mm out | Thin |
| Curing | At least 7 days | None |
| Finish | Needs putty for smoothness | Smooth, ready for paint |
| Wet areas | Suitable with waterproofing | Not suitable |
Mix and Thickness
| Location | Mix | Thickness |
|---|---|---|
| Internal | 1:6 (cement) | About 10 – 12 mm |
| External | 1:4, two coats | About 15 – 20 mm |
Thicker or richer plaster shrinks more and cracks more.
Common Mistakes
| Mistake | Result |
|---|---|
| Plastering the day after laying | Cracks as the wall dries |
| Thick plaster to hide poor laying | Shrinkage cracks |
| No mesh at junctions | Vertical cracks at columns |
| No curing | Crazing and weak plaster |
The Short Version
Wait a week, mesh the junctions, dampen, bond, plaster thin and lean, and cure — or use gypsum indoors. AAC's flatness is the advantage; thick plaster throws it away.
