What Is a Skim Coat?

A skim coat is a thin layer of finishing plaster (typically 2–3 mm) applied over plasterboard or an undercoat plaster to create a smooth, flat surface ready for painting or wallpapering. In the UK, the most commonly used skim coat plaster is Thistle Multi-Finish.

When Is Skim Coating Needed?

• Over new plasterboard (dot and dab, stud walls, ceilings)
• Over bonding coat or browning undercoat
• To refresh existing plaster that is sound but rough or patchy
• After removing wallpaper if the underlying plaster is damaged
• To cover filled holes and create a seamless finish

Application

Multi-finish is applied in two thin passes. The first pass is spread firmly to ensure adhesion, then the second pass is applied while the first is still wet and trowelled up to a smooth finish. The skill is in the trowelling — timing, pressure, and technique are what give a professional flat finish.

Coverage and Drying

A 25 kg bag of multi-finish covers approximately 9–12 m² at 2 mm thickness. Working time from mixing is around 40–60 minutes. The skim coat is touch-dry in about 24 hours but can take several days to dry fully (pink colour fading to white), depending on ventilation and room temperature.

Skim vs Plaster

In everyday UK trade language, “skimming” refers specifically to applying the thin finishing coat. “Plastering” can mean either the full two-coat system (undercoat plus skim) or just skimming, depending on context. When getting quotes, clarify whether the price is for skim only or full re-plaster.