Painting new plaster and plasterboard in Geneva: drying, primer, steps

Why new plaster cannot be painted straight away

On a new-build site, as in a major refurbishment, a freshly plastered wall looks finished well before it really is. Fresh plaster or a skim coat is not an inert surface: it keeps drying and carbonating for days, sometimes weeks. Until that process is complete, the surface releases moisture and stays chemically active.

Painting over it amounts to sealing that moisture under a watertight film. The result is well known: blistering, peeling in patches, stains and water marks bleeding through, sometimes salt efflorescence at the surface. The paint does not bond durably, and the repair costs more than the wait would have.

The waiting time is not a site promise: it is a physical fact. It depends on the thickness applied, the ventilation of the room and the season. A well-aired flat in summer dries faster than a closed-up winter apartment. That is why we do not rely on a date set in advance but on a moisture-meter check of the surface. This logic of a surface dry all the way through is the same as for a wall that flakes or blisters after too much moisture.

Plaster is highly absorbent: the role of the priming coat

Once the surface is dry, a second trap awaits: absorption. Plaster, skim coat and the cardboard face of a plasterboard all soak up paint, and not evenly. A finish applied directly penetrates irregularly, drags under the roller and leaves visible touch-ups under the light.

This is where the priming coat, also called a sealing primer, comes in. Its role:

• regulate the absorption of the surface so the finish stretches out evenly;
• anchor the finishing paint on a stabilised base;
• even out areas of differing absorption — typically the cardboard board and the filled bands of plasterboard.

Without this coat, you get uneven sheen, touch-ups that show and the appearance of joints. The exact product is chosen according to the surface and the manufacturer’s data sheet; this choice is part of the diagnosis carried out during the visit.

”Joints showing through”: understanding and avoiding the defect

This is the classic disappointment of poorly prepared new plasterboard: a few days after painting, in daylight, you can make out the pattern of the bands and joints through the finish. The wall is not dirty — it is uneven in sheen.

The explanation is simple. The plasterboard is covered with a cardboard face that absorbs little, while the jointing bands are filler, far more absorbent. If the finish is applied without an even primer, it soaks in differently from one area to another. Raking light does the rest and reveals the line of the joints.

Symptom observed	Likely cause	Typical repair
Pattern of bands visible	No even primer	Priming coat over the whole surface, then finish
Uneven sheen	Uneven absorption of the surface	Sealing primer, light sanding, matt finish
Touch-ups and joins that drag	Absorbent plaster not sealed	Regulating primer before the coats
Blisters or stains bleeding through	Surface not dry to the core	Let it dry, moisture-meter check, then prime
Rough grain to the touch	Insufficient sanding of bands	Light re-filling, fine sanding, dusting off

The answer is not a miracle product but a method: treat the bands, sand fine, dust off, then prime the whole surface — board and joints — before the finish. A check under raking light at the end of the job confirms that nothing shows through.

The right sequence, from dry surface to finish

A lasting paint job on new plaster or plasterboard follows a physical order, with no shortcut.

1. Dry and carbonated surface — moisture is checked first. As long as the surface releases water, we do not proceed. This step conditions everything else.
2. Treating bands and joints (plasterboard) — filling the joints, fine sanding, repairing any surface defects.
3. Careful dusting off — a dusty surface compromises the adhesion of the primer. We dust off after each sanding.
4. Priming coat / sealing primer — over the whole surface, to regulate absorption and even out board and filler.
5. Two finishing coats — the first sometimes lightly thinned depending on the product, then the even, stretched finishing coat.

Between coats, drying takes a few hours depending on the data sheet and the ventilation; a faint residual smell may linger for a day or two. Renovhome SA uses paints with low VOC emissions. This order — preparation, suitable primer, finish — is also what structures the pricing: see how we price a quote and the detail of our interior painting service.

New-build site in Geneva: coordination and the right time to step in

The canton’s new developments — La Praille, Sécheron, Pont-Rouge and the major refurbishments of older buildings in Eaux-Vives or Plainpalais — require a sequence of trades. The plasterer fits and fills; the painter comes next, once the surface is stable.

Renovhome SA carries out painting, finishes, the skim coats linked to painting and joint touch-ups on plasterboard. Heavy plastering, fitting new dry partitions or masonry are not painting work: on these points we coordinate our intervention with the plasterer and honestly refer you to the right trade. This is also the logic of the order of works in a renovation.

The right time to step in is not a slot in the schedule, it is a state of the surface. A visit allows us to check the moisture, define the suitable primer and sequence the painting with the rest of the site — rather than painting too soon and having to redo everything afterwards.