Term: undercoat

In painting, an undercoat is a type of paint or primer layer applied to a surface before the final topcoat. Its primary purpose is to:

• Provide a uniform surface for the topcoat to adhere to
• Improve adhesion between the surface and the finishing coat
• Enhance durability and longevity of the paint job
• Block stains or previous colours, especially when transitioning between dark and light shades
• Seal porous surfaces, such as bare timber or plaster

Undercoats are commonly used on surfaces like timber, metal, and previously painted walls, and are especially important when changing colours or painting over patched or repaired areas. In Australia, using the correct undercoat is essential for achieving a professional, long-lasting finish, particularly in harsh climate conditions.