Do you need primer before painting?

Short answer: bare, patched or stained surfaces need primer. Sound paint often doesn't

Primer goes on when a surface can't hold the topcoat well by itself. The paint makers name these cases:

• Bare or new surfaces. Haymes says any new surface that hasn't been painted before, like bare wood, brick or plaster, needs a primer or sealer for the paint to stick properly.
• Patches and repairs. Dulux says to spot prime filler repairs before the topcoat goes on.
• Stains. Haymes says an undercoat stops marks like watermarks or smoke residue seeping through the new paint.
• Covering a dark colour. Dulux says covering a dark colour needs an undercoat.
• Old oil-based paint. Haymes says water-based paint won't stick to old oil-based paint without a primer made for the job.

The other half of the answer matters just as much. Haymes says an existing topcoat can act as the gripping layer in some cases. So a sound, clean wall in a similar colour can often go straight to the topcoat. It still needs a wash, a light sand on any shiny spots and a dab of primer on any filled holes, which is what Dulux's Wash&Wear instructions ask for.

Primer, sealer and undercoat: the words for the first coat, and the jobs behind them

Haymes uses undercoat, primer and prepcoat as names for the same first layer, the one that goes on before the topcoat. It says that layer's main job is grip and coverage. Plenty of primers carry all three words in the product name. Dulux 1Step Prep, Taubmans 3 in 1, Haymes Prepcoat Ultracover and Wattyl Aqua Prep are all sold that way, as one product doing all three jobs.

The three words still hint at three jobs. Priming is grip. Haymes says primers and sealers stick to the surface and give the topcoat something to hold onto. Sealing stops a thirsty surface soaking up paint. Haymes says priming new surfaces seals them so the paint doesn't soak in and need extra coats. Undercoating gives an even base that hides what's underneath. Dulux says an undercoat can hide a dark colour better than extra topcoats.

Specialist primers sit outside that all-rounder group. Metal primers, etch primers, masonry sealers and stain blockers each suit a narrower job. Some makers also sell a separate sealer or undercoat, like the sealer binder Dulux lists for set plaster. The table below shows where you'd reach for one.

Surface by surface: what goes on first

Match the first coat to the surface. Here's what the makers' instructions say for the surfaces you'll find in most Sunshine Coast homes, inside and out.

Tannin needs a word of its own. Dulux says tannins are water-soluble compounds in some timbers, and it names meranti, merbau, jarrah, spotted gum, blackbutt and ironbark as Australian timbers that can carry them. That's why new tannin-rich timber gets a stain-blocking primer. For weathered tannin-rich timber, Dulux lists three coats of Weathershield instead. More detail for each surface sits in our guides to rendered walls, weatherboards, rusted metal and gutters and doors, skirting and frames.

Painting over old paint: test the grip first, then decide on primer

You can paint over old paint without primer when it's sound, clean and not too shiny, and you're keeping a similar colour. Our room painting guide has the full prep order. This is just the primer decision, step by step.

1. Test the grip. Dulux's test is a small X cut through the paint, tape pressed hard across it, then torn off. If paint lifts, Dulux says it's unsound and has to come off. Test several spots.
2. Wash it. Dulux's Wash&Wear instructions want the wall clean, dry and free from dust, oils and grease before any coat.
3. Check the shine. Glossy paint gets sanded to a dull finish. For very glossy surfaces, Dulux names 240 grit sandpaper.
4. Work out what's on there. If it's old oil-based enamel and you're going water-based, Haymes says you need a primer that bridges the two.
5. Look at the colour jump. Dark to light needs an undercoat, according to Dulux.
6. Spot prime the patches. Anywhere you've filled gets primer before the topcoat. Haymes notes an undercoat isn't a filler, so fill and let it cure first.

If your home was built before 1970, the Queensland Government says lead-based paint has probably been used, so get the old paint tested before you sand it.

Pass all six and you can usually go straight to your topcoat. Haymes adds one caution. Under many layers of old paint, a primer is often what keeps the new coat stuck to the original surface.

Self-priming paint covers most surfaces, and the label still lists exceptions

Self-priming paint saves a separate primer on many surfaces, but its own label still lists the ones that need one. Dulux describes Weathershield as self-priming on most surfaces. The same product's instructions still call for 1Step Prep on bare hardwood, an oil-based primer or stain blocker on new tannin-rich timber, and metal primer on rusty steel and on galvanised iron near the sea.

Inside, it works the same way. Dulux's Wash&Wear wall paint goes onto a sound painted wall after a clean, yet its instructions put a coat of 1Step Prep under it on unpainted plasterboard, brick, cement sheet and bare timber. On the primer side, Taubmans says its 3 in 1 grips aged enamels and glossy finishes even without sanding. Wattyl says Aqua Prep is made to stick to most surfaces, especially enamels. Both are primers you put under a topcoat.

The simple rule: read the label on the topcoat you've bought, find the line for your surface, and follow its primer advice.

Dulux 1Step Prep takes one coat: coverage and recoat time

Dulux says one coat of 1Step Prep is enough on most surfaces, with a second sometimes needed on new paper-faced plasterboard with jointing compound to get an even finish. Here's what two makers publish for their all-in-one primers.

Some Dulux instructions do call for two coats. Dulux's interior prep guide lists two coats of its Precision Maximum Strength Adhesion Primer, and the Weathershield instructions list two coats of metal primer on rusty steel. To work out how much you need, divide the area by the coverage. At 14 square metres per litre, 42 square metres of wall takes about 3 litres for one coat.

Timing matters outside. Dulux says the topcoat should go on no more than one week after 1Step Prep. And spraying isn't recommended for priming timber, so brush or roll it on.

When priming becomes a job for a painter

Priming a bedroom or a set of doors is fair DIY. Some jobs are better handed over:

• Stairwells, voids and high ceilings, where you'd be working from a ladder on the stairs. Our room painting guide covers the ladder limits.
• Old paint that fails the tape test across whole walls. At that point the job is stripping old paint before any primer goes on.
• Second-storey exteriors, and rusty steel that needs every bit of rust removed and two coats of metal primer before the topcoats.
• Old oil-based trims through a whole house, where every door, frame and skirting needs sanding and a bridging primer.

If the only way to reach the top of a wall is a ladder standing on a stair, stop. Get a painter with proper access gear for that height.

What priming means for your painting quote

Priming adds prep time and product to a quote. A room of sound walls in a similar colour needs little of it. A room of new plasterboard, patched walls, old gloss trims or a dark colour going light needs much more. Our interior painting cost guide shows how wall condition and colour change the price.

Our interior house painters and exterior house painters work across the Sunshine Coast. Check our locations page for the suburbs we cover. We hold QBCC licence 1281728, and you can get a guide price from our instant estimate before we come out and look at the surfaces.