Paint & Finishes
Primer / Undercoat
A preparatory coat that seals porous surfaces, blocks stains, and gives the finish coat something consistent to bond to.
Best for
- Bare drywall, plaster, or wood
- Covering dark colours before a light repaint
- Blocking water stains, marker, or smoke residue
Avoid when
- A previously painted wall in good condition and a similar colour, where it adds cost without benefit
Why skipping it costs more
Bare or heavily patched surfaces are porous and absorb paint unevenly, leaving flashing (patches of different sheen). Primer evens out absorption so the finish coat goes on consistently, often turning a needed three coats of colour into two.
Stain-blocking primer is a different product
Standard primer will not reliably block water stains, nicotine, or marker. A shellac- or oil-based stain-blocking primer is worth the extra cost specifically for those problems.
Put this into practice
- Paint CalculatorHow much paint do I need for this room?