What a primer is used for
Primer is used to improve adhesion, regulate absorbency and stabilize weak or uneven substrates before painting or coating. Different surfaces need different primer behaviour, which is why there is no single universal answer for concrete, screed, plaster, tiles, masonry and wood. The correct primer is usually chosen by the substrate first and the finishing system second.
Bonding primers, deep primers and undercoats
Bonding primers are the practical choice where smoother or difficult surfaces need a better grip for the next layer. Deep penetrating primers are more useful on absorbent or sandy mineral substrates where consolidation and even absorption matter. Undercoats and specialist system primers become important when a floor coating, tile paint or demanding decorative finish needs a more controlled build-up.
Why primer choice affects the whole system
When the wrong primer is used, even a good topcoat can lose adhesion, dry unevenly or wear earlier than expected. Clean surfaces, stable edges and the right drying time also matter just as much as the product itself. A primer works best as part of the overall coating system rather than as an isolated first step.