Last checked 4 Nov 2026 against the sources at the end of this page.
You need a primer before painting when the surface is bare, new, patched, chalky, glossy, or a material the paint won't grip on its own. A wall that's been painted before, is still sound and is staying a similar colour usually goes straight to the top coat.
Most homes have some of each. In a resale flat, the living room walls might only need a wash before the colour goes on, while the kitchen's new skim coat needs a sealer and the gate outside needs a metal primer. The table further down sorts them surface by surface.
In short
- Primer is the first coat on a bare surface, and its job is to make the paint stick.
- New plaster, bare wood and bare metal need a first coat before the colour, and so do tiles and glossy paint.
- On masonry walls the first coat is often sold as a sealer. On wood and metal it's a primer with an undercoat on top.
- Paint and primer in one tins work on sound, painted walls, but the makers still say to use a separate primer on stained or slick surfaces.
Why painters prime a wall before painting it
Paint is made to look good and wear well. Primer is made to grip the surface and give the paint something even to hold on to.
Nippon puts it simply in its primer and undercoat guide (read 4 Nov 2026): a primer sealer penetrates the surface so the coats on top adhere well. Wall primers sold here also deal with what's in the wall. Jotun describes its Majestic Primer (read 4 Nov 2026) as an alkali-resisting primer that improves adhesion and forms an alkaline and water-resistant barrier under the paint.
How to tell if your wall, door or gate needs a primer
| Surface | First coat before painting? | What goes on first |
|---|---|---|
| Fresh cement plaster or skim coat | Yes | An alkali-resistant wall sealer, once the plaster is dry |
| Wall painted before, sound, similar colour | Usually not | Clean it, then the top coat |
| Chalky, powdery or stained wall | Yes | A sealer that binds the surface |
| Patched or replastered spots | Yes, on the patches | Spot-prime so the patch doesn't show through |
| Bare wood: doors, frames, skirting | Yes | Wood primer, then an undercoat |
| Bare iron or steel: gates, grilles | Yes, straight away | An anti-corrosive metal primer |
| Aluminium, galvanised steel, PVC, tiles, glass | Yes | A bonding primer made for slick surfaces |
| Gloss or semi-gloss paint | Sand first, then prime | Sanding removes the gloss so the next coat can grip |
The table follows what the paint makers say on their own product pages, all read 4 Nov 2026:
- Nippon's Expresskote Sealer is made for new and old cement-rendered surfaces, and Nippon says it can be applied 3 days after plastering.
- Several Nippon product pages, Expresskote Sealer among them, ask for moisture below 4% before application, so a damp wall waits, primer or not.
- Nippon's Bodelac 9000 Undercoat page says all exposed metal must be primed immediately to prevent corrosion, and that bare wood gets a wood primer before the undercoat.
- Dulux Primer is a solvent-based anti-corrosive primer for indoor and outdoor ferrous metalwork, new or weathered iron and mild steel.
- Nippon's Multi-Surface Primer is for surfaces paint struggles to stick to, including aluminium, PVC pipe, laminate, tiles, galvanised steel and glass. Nippon says glazed tiles should be sanded first.
- Nippon's Aqua Primer Sealer Undercoat page says a high-gloss or semi-gloss surface should be sanded to remove the gloss so the new paint adheres.
Primer, sealer or undercoat: which one is on your quote
The three words get used loosely, so here's how the makers use them.
A primer is the first coat on a bare surface. You'll mostly see the word on wood and metal products.
A sealer is the first coat on masonry: cement, plaster, skim coat and old chalky walls. Dulux Sealer (Water-based) (read 4 Nov 2026) is made for brickwork, plaster, cement and textured walls, new or previously painted, and Dulux lists improved adhesion and alkali resistance among its features. For when a wall needs one, read our sealer paint guide.
An undercoat goes on top of the primer, mainly on wood and metal, before a gloss finish. Nippon's guide says an undercoat fills imperfections such as grain marks or ridges and leaves the surface flat and ready for the finishing coat.
Some tins do more than one job. Nippon calls its Aqua Primer Sealer Undercoat a one-step pre-coat for masonry walls, ceilings, wood, metal and plastic. So if your quote lists a "primer sealer" for the walls and an "undercoat" for the doors, it's naming two different coats for two different surfaces.
Does paint and primer in one let you skip the primer?
Often, on a wall that's already painted and in good shape. On stained or slick surfaces, the makers themselves say to use a separate primer.
These tins are real products. Raffles Paint describes its R.ONE (read 4 Nov 2026) as an interior paint with a built-in primer and sealant. Benjamin Moore's page on paint and primer in one (read 4 Nov 2026) is clear about the limits. It says these paints are self-priming on most properly prepared surfaces, and still recommends two coats, with two coats on bare surfaces. For a surface that's water-stained, smoke-damaged, grease-stained or very slick, it points you to a separate primer.
So a paint and primer in one tin still needs a clean, prepared surface. It won't stand in for a metal primer on a gate, or a bonding primer on glazed tiles.
Why skipping the primer shows up as peeling paint
Paint holds on to whatever it touches first. If that's a layer of chalky old paint or dust, the new coat is stuck to something loose, and the whole lot lifts off together. Gloss gives it nothing to key into at all. On bare steel the trouble starts underneath, as rust, which is why Nippon says exposed metal must be primed straight away.
New plaster can stain paint from behind. Nippon lists a chemical barrier to salt migration on its Aqua Primer Sealer Undercoat, and says its Vinilex 5170 Wall Sealer (read 4 Nov 2026) resists efflorescence, the white salt bloom that discolours a new wall.
Already peeling? Primer is only one of the causes. Our guide to why paint peels fast in Singapore goes through the others, from damp walls to rushed drying times.
When you can paint without a primer
You can usually skip it when the wall has been painted before, the paint is sound, there's no chalk on your fingertip when you rub it, and the new colour is close to the old one. Wash off dust and grease, fill small holes, and let it dry.
A small touch-up on sound paint with the same product doesn't need a primer either. Spot-prime only where you've filled a hole or reached bare plaster.
When proper prep saves you a second repaint
One extra coat at the start is far less work than stripping and repainting a wall that peeled. A painter is the safer call when one job covers several surfaces, say skim-coated walls plus a metal gate, because each needs its own first coat and its own drying time. It also makes sense after plastering, when the wall has to dry out before anything goes on.
The same team plasters, repairs spalling and paints, so the plastering and the first coat are planned together. If you're replastering first, see wall plastering. We record the paint brand, product, colour code and batch for your address, so a touch-up later goes on with the same paint.
Sources
- Nippon Paint Singapore, Importance of primer and undercoat, read 4 Nov 2026
- Nippon Paint Singapore, Aqua Primer Sealer Undercoat product page, read 4 Nov 2026
- Nippon Paint Singapore, Expresskote Sealer product page, read 4 Nov 2026
- Nippon Paint Singapore, Vinilex 5170 Wall Sealer product page, read 4 Nov 2026
- Nippon Paint Singapore, Multi-Surface Primer product page, read 4 Nov 2026
- Nippon Paint Singapore, Bodelac 9000 Undercoat product page, read 4 Nov 2026
- Dulux Singapore, Dulux Sealer (Water-based) product page, read 4 Nov 2026
- Dulux Singapore, Dulux Primer product page, read 4 Nov 2026
- Jotun Singapore, Majestic Primer product page, read 4 Nov 2026
- Raffles Paint, R.ONE product page: interior paint with built-in primer and sealant, read 4 Nov 2026
- Benjamin Moore (US site), Paint and primer in one: coats and when to use a separate primer, read 4 Nov 2026