Primer Coverage Calculator — How Much Primer Do I Need?

Yes — new plaster must always be primed before applying emulsion. Fresh plaster is highly porous and will absorb paint unevenly, causing a patchy finish. The standard approach is to apply a mist coat — emulsion diluted with water (typically 70% paint, 30% water) — before applying full-strength top coats. Alternatively, use a dedicated plaster primer such as Dulux Plaster Primer.

For bare wood, use a dedicated wood primer such as Dulux Wood Primer or Zinsser Bulls Eye. Water-based primers are fine for interior wood. For exterior wood or areas prone to moisture, oil-based primers provide better protection. Knotting solution (shellac-based) should be applied to any knots before priming to prevent resin bleed-through.

Coverage depends on the surface type. New plaster absorbs heavily and covers only about 8 m² per litre. Bare wood covers approximately 10 m²/L. Previously painted surfaces in good condition cover 12 m²/L, and metal surfaces cover around 14 m²/L (metal primers range from roughly 10 to 18 m²/L depending on the product). These are typical, conservative UK trade figures consistent with Dulux, Zinsser and Crown datasheet ranges — always check the coverage stated on your specific primer's tin before ordering.

PVA should not be used as a primer on new plaster for painting. While PVA seals the surface, it creates a non-porous film that can cause paint to peel. Instead, use a mist coat (diluted emulsion) or a dedicated plaster primer. PVA is only appropriate as a bonding agent before plastering, not before painting.

One coat of primer is usually sufficient for previously painted surfaces in good condition. Two coats are recommended for very porous surfaces (new plaster, bare softwood), when covering stains or strong colours, and when using shellac primer to block stubborn stains. Always allow the first coat to dry fully before applying the second. After priming, use our Paint Coverage Calculator to work out how much top-coat paint you need.