Primer is a layer of paint applied to seal, bond, and provide a firm foundation to prepare a substrate surface for the application of a topcoat. Undercoats are mostly used on wood substrates and have either an alkyd or latex or lacquer formulation.
An undercoat paint also works as a primer, but a primer is not always an undercoat as both serve different functions. A primer is the first coat that is applied directly to a bare substrate surface used to seal the surface to keep the paint application from bleeding through and cracking. Primers also prevent stains and moisture from keeping subsequent coats from staining and sinking into the substrate.
Primers act as a foundation for your new paint to adhere to while undercoat paint creates a flat and level base for the topcoat. Sealers can be used instead of primers sealing off surface porosity and providing good adhesion between the substrate and the fresh paint. Sealers also create a barrier between incompatible finishing coats to inhibit moisture penetration.
Build world has a range of primers, sealers, topcoats and undercoats at our online store, some with built-in fungicides to prevent mould growth on the existing surface. Our brands include Bostik, Crown, Leyland, and more.