Berger Undercoat 750ml White, primer base coat, paint undercoat for wood and metal, high coverage undercoating paint, solvent based undercoat

Primers and undercoats are the first layers of a paint system. A primer seals a bare or new surface and gives the following coats something to grip. An undercoat goes between the primer and the topcoat, building a smooth, opaque base and improving adhesion between the layers. This category covers wood, MDF, metal and multi-surface primers, combined primer undercoats, and undercoats in water-based and solvent-based types, including aerosols.

Matching the primer to the surface

• Bare wood: treat knots with knotting solution, then apply a wood primer, giving end grain extra attention. The timber should be dry before priming.
• MDF: use a primer made for MDF.
• Metal: use an anti-rust or metal primer on bare steel and iron, and spot prime any exposed nail heads in woodwork.
• Difficult surfaces: multi-surface and adhesion primers are made for surfaces where an ordinary primer may not grip; check the tin for the surfaces listed.
• Primer undercoats: do both jobs in one product. Quick-drying water-based versions for wood can often be recoated after a few hours, and new or bare wood usually needs two coats.

Preparation and application

Make sure surfaces are sound, clean and dry, free from dust, grease and dirt. Remove loose or flaking paint by scraping and sanding, and sand bare wood along the grain. Apply primer, then one coat of undercoat, then the topcoat, and check that each product is listed as compatible with the next. Water-based undercoats dry quickly with low odour, and solvent-based products need white spirit for cleaning brushes. Follow the manufacturer's instructions and safety data, and use solvent-based paints in a well-ventilated area.

For topcoats, browse paint; for sandpaper and sanding blocks, see abrasives.