Module 3: Skimming & Finishing Techniques
Skimming and finishing are the final, most delicate stages of plastering, where the surface is transformed into a smooth, polished, or textured wall ready for painting or decoration. This module focuses on applying the topcoat (skim coat), refining the surface, and mastering advanced techniques for a professional-quality finish.
1. Skim Coat Application
The skim coat is a thin, fine layer (2–3mm) of plaster applied over the cured base coat to create an even surface. Common materials include:
Multi-Finish Plaster (Gypsum) – Ideal for interiors, easy to trowel smooth.
Lime Putty – Used for heritage or breathable wall finishes.
Venetian Plaster – Decorative polished finish with marble dust effects.
Steps for Skim Coating:
Pre-Wetting the Base Coat: Lightly dampen the surface to prevent rapid suction and improve workability.
Mixing the Skim Plaster: Blend to a creamy, lump-free consistency. Let it rest (slake) for 1–2 minutes before remixing.
Applying the First Pass: Load the trowel and spread the plaster in long, sweeping arcs, covering small sections (1m² at a time). Maintain even pressure to avoid ridges.
Laying Down (First Troweling): After 10–15 minutes (when firm but not dry), smooth the surface with a clean steel trowel held at a 10–15° angle, removing excess material.
Second Troweling (Wet Finish): As the plaster begins to set (20–30 minutes later), lightly spray with water and polish in circular motions for a glass-like finish.
2. Advanced Finishing Techniques
Depending on the desired aesthetic, different methods can be employed:
Sponge Finish: For a subtle texture, gently run a damp sponge over the surface.
Trowel Texture: Create patterns (e.g., swirls, arcs) by manipulating the trowel edge.
Polished Plaster: For luxury finishes like Venetian plaster, burnish with a flexible stainless-steel trowel in multiple layers.
3. Troubleshooting Common Issues
Cracking: Caused by rapid drying (avoid drafts, use retarders if needed).
Blisters: Due to over-troweling or trapped air (press firmly during application).
Ridges: Uneven trowel pressure (keep the blade flat and clean).
4. Final Checks & Aftercare
Inspect under side lighting to spot imperfections.
Allow proper drying (24–48 hours for gypsum, longer for lime).
Lightly sand minor flaws with fine-grit sandpaper before painting.
This module equips learners with the precision skills needed for flawless finishes, whether for modern smooth walls or decorative effects.
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