Applying Solid Plaster to Walls, Ceilings and Internal Surfaces
Coats, timing and technique
Internal solid plastering is a sequence of coats applied at the right thickness and the right time. Questions test coat order and purpose, thickness limits, and how to avoid shrinkage cracking and poor adhesion.
Core concepts to know
- Coat sequence: backing or first coat, then floating or second coat, then finish or setting coat. Each has a purpose: build thickness, level and key, then provide the final surface.
- Thickness limits: keep each coat within the specified maximum; thick single coats shrink and crack, so build up in layers. Follow the specification for the system in use.
- Keying between coats: scratch the surface of the backing coat to provide a mechanical key for the next coat.
- Timing: apply the next coat when the previous one has taken up but not dried out; too wet causes slumping, too dry causes poor bond.
- Ceilings: work overhead with the correct hawk and trowel technique, control the mix consistency so it does not fall, and use trestles or podiums safely.
- Finishing: float and trowel to the specified finish, avoiding over-trowelling which brings water to the surface and weakens it.
Traps
Distractors include skipping the key between coats, applying a thick single coat to save time, or trowelling a finish too early while the material is still wet. Another trap is treating a setting coat as a levelling coat.
Worked rule of thumb
Think of each coat as doing one job only: build, level, finish. If you are trying to level and finish in one pass, or build thickness in one coat, you are creating the crack or hollow spot you will later have to repair.