What are the types of primer paint and when do I need each one?

Primer paint is a preparatory coating applied before the topcoat. The right type depends on the surface and the problem you are solving.

On new plaster, concrete, or cement surfaces, an alkali-resistant wall primer is required before interior or exterior painting. It seals the alkaline salts in new walls and provides a stable base for the topcoat. On new unpainted surfaces this step cannot be skipped.

Bare wood needs a dedicated wood primer. It seals the grain, prevents tannin bleed from dark timbers, and stops the topcoat from absorbing unevenly — giving the final finish a smoother, more consistent result.

Metal surfaces such as iron, steel, and aluminium need their own primer. The purpose here is corrosion protection and adhesion. Stain-blocking primer is used over stubborn marks — water stains, nicotine, tannin — that would bleed through a standard emulsion.

Paint-and-primer-in-one products are suitable only when repainting over a clean, sound, non-porous surface in a similar colour. They are not a substitute for a proper primer on new, bare, or stained surfaces.