The right paint primer depends on the surface: new plaster and cement walls take Plaster Primer, chalky or powdery concrete takes Clear Bonding Liquid, bare metal takes a metal primer, and going from a solvent to a water-based coat takes Universal Undercoat. The primer is what makes paint stick and last, so matching it to the surface matters more than the topcoat. This guide matches each primer to its surface and answers the common priming questions.
What does a paint primer do?
A paint primer seals and stabilises the surface, gives the topcoat something to grip, and evens out how the surface absorbs paint. On new plaster it neutralises alkalinity that would otherwise attack the topcoat; on porous or chalky surfaces it binds the loose top layer so paint does not peel; on non-porous surfaces it creates a key for adhesion. Skip the primer on a surface that needs one and the topcoat peels, flashes patchy, or lifts within a season. The primer is the foundation the whole paint job stands on.
Which primer for which surface?
Match the primer to the surface and its condition. Use this table as the starting point:
| Surface | Primer |
|---|---|
| New plaster & cement walls | Plaster Primer (alkali resistant) |
| Budget walls & ceilings (primer + topcoat in one) | MultiPrime |
| Chalky, powdery or porous concrete | Clear Bonding Liquid |
| Before plaster work, or water-based concrete primer | Bond & Key |
| Going from a solvent-based to a water-based coat | Universal Undercoat |
| Bare metal, steel, gates, galvanised | a metal primer — see metal primer guide |
| Interior damp walls | Damp Proof |
Is it necessary to prime before painting?
Yes, prime whenever the surface is new, bare, porous, chalky, glossy or a different type from the old coating; a sound, previously painted surface in good condition can often be recoated without it. New plaster, bare metal and powdery concrete always need priming. A wall that already carries sound paint and is just changing colour usually does not. The test is simple: if the surface is raw, unstable, or the paint has nothing to grip, prime it. If it is stable and the same paint type is going back on, a clean and light sand may be enough.
Can I apply primer directly on a wall?
Yes, primer goes straight onto a clean, sound, dry wall — that is exactly its job. On a new plaster wall, brush or roll Plaster Primer directly onto the cured plaster, let it dry, then topcoat. Clean off dust and loose material first, and let new plaster cure before priming. What you do not do is put a topcoat straight onto raw plaster or chalky concrete without the primer, because that is what fails.
Primer for new plaster and cement walls
New plaster and cement walls take an alkali-resistant plaster primer, because fresh plaster is highly alkaline and will attack a topcoat applied straight onto it. Plaster Primer is the high-performance first choice; MultiPrime is the budget option that works as a primer and topcoat in one on walls and ceilings. Let new plaster cure fully before priming. The full detail is in the guide to plaster primer.
Primer for chalky, porous and problem surfaces
Chalky, powdery and porous surfaces take a bonding primer that binds the loose top layer and seals the surface. Clear Bonding Liquid stabilises dusting concrete and chalky plaster so the topcoat grips, and it primes before Concrete Enamel or 1K Polyurethane on floors. For difficult and damp surfaces, see the guide to priming damp and problem surfaces.
Primer vs undercoat: what is the difference?
A primer prepares and seals a bare or problem surface, while an undercoat builds an even, opaque base between the primer and the topcoat. They are not the same product and often both are used: prime the raw surface, then undercoat to even out colour and build before the finish coat. Universal Undercoat also bridges a solvent-based old coat to a water-based new one. The full comparison is in the guide to primer vs undercoat.
Primer for metal
Bare metal needs a dedicated metal primer, not a wall primer, because it has to inhibit rust and grip a non-porous surface. New steel takes red oxide, galvanised takes an etch primer, and rusted metal takes an anti-rust primer. Wall and plaster primers do not protect metal. The full breakdown is in the guide to which metal primer to use.
Do primers come in colours?
Most primers are a neutral white, grey or clear, and the primer colour does not need to match the topcoat as long as the finish covers in two coats. A white or grey primer gives a neutral base that helps a light topcoat cover; a clear bonding primer leaves the surface its natural colour. What matters is that the primer seals and grips, not its shade. If you are covering a strong old colour with a pale new one, a light primer helps the topcoat reach full colour in fewer coats.
Can you use a primer as a topcoat?
Most primers are not made to be left exposed as a finish, with one exception: a multi-surface primer-and-topcoat like MultiPrime is designed to do both. A standard primer has no weather or wear resistance and will chalk or dirty quickly if used as the final coat, so it needs a topcoat over it. MultiPrime is the exception, formulated to work as a matt primer and finish in one on walls and ceilings where a separate finish coat is not needed. For anything exposed to weather or traffic, prime and then topcoat.
How long between primer and paint?
Let a primer dry for the time on its label — usually a few hours — before the topcoat, and do not leave it so long that it gathers dust or weathers. Most wall primers are ready to overcoat the same day in warm, dry conditions; solvent primers and cold or damp weather take longer. Overcoating too soon traps solvent and softens the film; leaving a primer exposed for weeks lets it collect dirt that weakens the bond. Prime and topcoat within the recoat window on the tin for the best result.
How much primer do you need?
Budget one coat of primer at roughly the same coverage as a coat of paint, more on porous or thirsty surfaces. New plaster and bare concrete drink the first coat, so allow extra. Primers come in 5 litre (L) and 20 L; the 20 L is the economical size for a full house or a large wall. Prices sit on each product page and the full price list. Measure the wall area and match it to the coverage on the tin.
What happens if you skip the primer?
Skipping primer on a surface that needs it causes peeling, patchy flashing, colour bleed and early failure, and it usually costs more to fix than the primer saved. The topcoat has nothing to grip or is attacked by alkalinity, so it lifts. See the guide to what happens when you skip primer.
Related guides
- Plaster primer: new plaster and cement walls
- Bonding liquid: sealing chalky and porous surfaces
- Primer vs undercoat
- Do you need to prime before painting?
- Metal primer: which one for which metal
Where to buy
Shop the full Primers range — Plaster Primer, Clear Bonding Liquid, Bond & Key, Universal Undercoat and MultiPrime — with national delivery, or visit our paint shops in Table View, Cape Town and Edenvale, Johannesburg. For trade pricing, call +27 84 985 6141.
