To a professional painter, primer is not just a base coat—it is the single most important element that ensures the bond between the substrate (the wall, wood, or metal) and the topcoat (the paint). Skipping this step or choosing the wrong primer is the leading cause of paint failure, resulting in peeling, staining, or poor colour adhesion.
The world of primers has expanded far beyond basic white undercoats. Today, specialist primers are engineered chemical solutions designed to perform three main functions:
- Adhesion: They stick tenaciously to tricky, non-porous surfaces (like ceramic tiles or glossy paint).
- Sealing: They seal porous surfaces (like new plaster or raw wood) so the topcoat doesn’t soak in unevenly.
- Blocking: They block stains (like smoke, watermarks, or wood knots) from bleeding through the topcoat.
Specialist primer guide
Understanding the chemical base of a primer is key to selecting the right product for a specific problem surface.
1. Shellac-based primers (The ultimate blocker)
- When to use: Use it on severe smoke damage, fire damage, heavy water stains, and most importantly, on knots in wood (shellac is the only substance that reliably prevents resin bleeding through paint).
- Pros: Dries extremely fast, blocks almost all stains and odours, and adheres well to difficult surfaces.
- Cons: High odour (requires excellent ventilation), equipment cleanup requires methylated spirits.
2. Oil/Solvent-based primers (The heavy-duty sealer)
- When to use: Ideal for exterior wood, bare metal (where corrosion is a concern), and heavily porous interior surfaces.
- Pros: Excellent for rust prevention, deeply penetrates wood, and offers a tough, durable base.
- Cons: Slow drying time (up to 24 hours), high VOCs (strong odour).
3. Water-based acrylic primers (The versatile gripper)
- When to use: Best primer for surfaces, tiles, laminates, and new drywall. It is highly flexible and adheres to surfaces that traditional primers would struggle with.
- Pros: Low odour, fast drying, easy cleanup (water), excellent for interior use.
- Cons: Less effective on heavy stains or oily residues than shellac.
Matching the primer to the tricky surface
Knowing how to apply primer for a given substrate is the hallmark of a skilled professional.
| Difficult Surface | The Problem | Recommended Primer Type |
| Glossy Tiles/Laminates | Poor adhesion—paint just slides off. | Water-based adhesion primer |
| New Plaster | Highly porous and absorbent, leading to flash-drying and uneven colour. | Specialist vinyl matt ‘mist coat’ (diluted emulsion) or a water-based stabilising primer. |
| Smoke/Fire Damage | Odour and carbon stains bleed through paint. | Shellac-based primer to block stains and seal odours permanently. |
| Aged uPVC/Plastics | Needs flexibility and maximum adhesion. | Dedicated plastic primer or a high-adhesion acrylic primer (lightly scuffed surface first). |
| Rusty Metal | Rust will continue to grow beneath the paint. | Anti-corrosive oil-based metal primer (e.g., red oxide) to encapsulate the rust. |
Primer application and the decorator’s edge
Even the best primer will fail if improperly applied. A key difference when you hire a professional is their disciplined approach:
- Prep is paramount: They thoroughly clean, degrease, and often lightly abrade (sand) the surface before priming. For instance, before using a primer guide for painters on uPVC, they will key the surface with a fine sanding pad to aid adhesion.
- Targeted Priming: They only apply specialist primers where needed. A large wall of new plaster might just get a mist coat, but the adjacent, old-stained window sill will get a targeted coat for blocking.
- Full Curing Time: Professionals respect the technical data sheet. While an acrylic primer might be touch-dry in 30 minutes, they allow the full recommended recoat time (often 2 hours or more) to ensure maximum chemical bond before applying the topcoat.
The cost of high-quality, specialist primer is a fraction of the cost of stripping and repainting a failed job. Investing in the right primer is not an extra cost; it’s a non-negotiable insurance policy against paint failure.
With Rated People, you have the power to get it done. Find a trusted, local tradesperson today.
