How do you paint new plasterboard?

Short answer: one sealer undercoat, then two topcoats

The paint system for new plasterboard is a sealer undercoat followed by two topcoats. Gyprock says it's vital that a plasterboard primer sealer goes on first, and it points to AS 2311 for the minimum of a sealer plus two coats of water-based paint. Dulux recommends the same system for new plasterboard: a water-based acrylic sealer undercoat, then two full coats of water-based acrylic topcoat.

The paint makers' own labels say the same thing. Dulux's Wash&Wear wall paint instructions put one coat of 1Step Prep on unpainted plasterboard, then two topcoats, with the first completely dry before the second. Haymes says freshly plastered walls need sealing before you paint them.

Sometimes the sealer takes two coats. Dulux says a second coat of 1Step Prep may be needed on new paper-faced plasterboard with jointing compound, to get an even finish. Its Prepcoat Acrylic Sealer Undercoat instructions also call for a second coat where the paper and the joint compound have different textures.

Why bare plasterboard needs a sealer before wall paint

New plasterboard is really two surfaces side by side. Gyprock explains that a standard Level 4 finish leaves the painter the paper face of the board and the jointing compound over the joins and screws, and the two have different textures and porosity. Paint soaks into one faster than the other.

A sealer evens that out. Resene's wallboard data sheet says sealing is needed to even out the porosity between the jointed areas and the paper face, so the paint system bonds well to the wall. Resene adds that the jointed areas are weaker than the surrounding board, so the sealer has to soak into them.

That's why a coat of ordinary wall paint isn't a stand-in. Resene says standard acrylics, including standard wall paints, aren't designed for this job and typically won't achieve the bond it needs. Filled dents and screw holes count too. Resene says filled spots need sanding smooth and sealing, or the topcoat can soak in unevenly and look patchy.

Painting new plasterboard step by step

Once the plasterer has finished and the joints are dry, painting new plasterboard follows the same order for walls and ceilings. These steps come from the Dulux, Haymes, Resene and Taubmans instructions.

1. Get the dust off. Resene says sanding dust has to come off before sealing. Wipe the jointed areas with a damp cloth, and don't scuff the paper face.
2. Cut in the sealer. Haymes says to brush the sealer into the edges first: frames, skirting boards, ceiling lines and corners.
3. Roll the sealer on. Haymes says to roll it on evenly and smoothly. Use the coverage on the tin to work out how much you need. Dulux lists 1Step Prep at 14 square metres per litre and Taubmans lists its 3 in 1 at up to 16.
4. Wait for it to dry. Dulux lists 1Step Prep as touch dry in 20 minutes and ready to recoat in 2 hours. Taubmans lists 30 minutes and 2 hours for its 3 in 1.
5. Sand the walls lightly. Dulux says walls should always be lightly sanded before the topcoats. Ceilings often aren't sanded unless it's high-end work. Dust off again.
6. Seal any filled spots. Patch dents now, sand them and seal them again, as Resene describes.
7. Apply two topcoats. Dulux says to cut in with a brush, then roll up to that edge while it's still wet. Let the first coat dry completely before the second.

Some colours need an extra coat. Resene says two coats over a sealed surface are generally enough, but some yellows and reds may need a third coat or a white basecoat.

Finish levels 3, 4 and 5: the plasterer's part of a smooth wall

How smooth a painted plasterboard wall looks depends on the finish level the plasterer worked to, before any paint goes on. Gyprock says AS/NZS 2589, the Australian standard for gypsum linings, defines three levels of finish for plasterboard walls and ceilings.

Gyprock says the skim coat in a Level 5 finish conceals flaws in the joint work and smooths the paper texture. For a Level 4 wall, Gyprock recommends a flat, matt or low sheen paint in a light colour. Gyprock also says the finish level for each area of the home should be set at the design stage, before the plasterers start.

Glancing light shows joins, and a flatter, lighter paint helps disguise them

Joins that show through new paint are often picked out by glancing light. Gyprock says some surface variation in plasterboard is inevitable. When light hits the board at an acute angle, it casts small shadows that pick out every ridge. Resene says light from windows and light fittings cutting across a wall or ceiling will highlight the joints and fixing points.

Paint choice can soften it. Gyprock says a matt finish diffuses the most light and helps disguise flaws, and recommends matt wherever a higher gloss isn't needed, such as ceilings. It says satin, semi gloss and gloss can make small variations stand out and should only go over a Level 5 finish. Colour matters as well. Gyprock says light colours scatter light better than dark ones, and a dark colour calls for a Level 5 finish.

Even Level 5 has limits. Gyprock says it reduces glancing light effects but can't be expected to remove them completely. Our interior paint finishes guide compares the sheens room by room.

Which sheen goes where on new plasterboard

On new plasterboard, the flattest sheen that suits the room usually gives the most even look. Dulux sets out where each sheen fits in its recommended system for new plasterboard:

That last row is the trade-off. Dulux recommends satin or semi-gloss for high-traffic or wet areas, and Gyprock says that higher sheen shows joins more. If you want semi-gloss walls or a deep colour in a room with big windows, raise Level 5 with the builder before the plasterer prices the job. Ceilings get the full treatment in our ceiling painting guide.

Spraying new plasterboard: back-roll every coat

New plasterboard can be sprayed, as long as each coat is rolled over while it's wet. Gyprock strongly recommends rolling all coats, because a roller leaves a light texture that minimises visible differences. If the paint is sprayed, Gyprock says to back-roll each coat while it's still wet and let it dry completely before the next.

Dulux gives the reason. It says spray alone leaves a very smooth finish that reflects more light, which makes surface variations and flaws easier to see. Back-rolling gives the paint a soft texture that scatters light more evenly. Dulux also says rolling flattens raised paper fibres left when the plasterer sanded the set joints.

Dulux says the sealer on ceilings should always be back-rolled after spraying, unless the ceiling is going to be sanded. Our guide to spraying or rolling interior walls covers the rest of that choice.

Renovations and extensions: what to settle with the builder and painter

On a renovation or extension, settle the finish level before the plasterboard goes up. Gyprock says builders and plasterers prepare the surface for painting, including even joints and the final sand. Resene says that preparation is the plasterboard fixer's job, and that unless it's agreed, the painter isn't expected to bring a Level 3 or 4 finish up to Level 5 without being paid for it.

• Ask the builder which finish level is in the plasterer's price, room by room.
• Flag rooms with big windows, skylights or downlights washing across walls. Gyprock names these as Level 5 rooms.
• Pick sheen and colour early. Gloss, semi-gloss or a mid to dark colour points to Level 5.
• Make sure the painting quote names the sealer and two topcoats.
• Look at the joins in the light the room actually gets before painting starts, and raise any ridges with the builder then.

Fixing, jointing and skim coating the sheets is plasterer's work, so leave it to them. In Queensland, the QBCC says anyone contracting for building work valued over $3,300 needs a QBCC licence, while owners doing work on their own property valued at no more than $11,000 don't. Its painting and decorating licence covers preparing surfaces and applying paint. Check the licence of whoever you hire.

What new plasterboard means for your painting quote

New plasterboard adds a full sealer coat, and sometimes a second one, plus a light sand before the topcoats. Our interior painting cost guide shows how wall condition changes the price.

Our interior house painters can look at your new walls and ceilings and quote the sealer and topcoats. For a home where the finish has to look right under strong light, see our high end project painters. We hold QBCC licence 1281728. See our locations page for the Sunshine Coast suburbs we cover, or get a guide price from our instant estimate.