Coats, drying time and smell: paint in practice in Geneva

How many coats: coverage is not a matter of opinion

The question comes up on every job: can we do just one coat? The honest answer is almost always no. Interior paint is built up in coats, and each one has a precise physical role.

In practice, the usual scheme is one primer (undercoat) + two finish coats. The primer regulates how the surface absorbs and bonds the finish; the two finish coats even out the colour and close the film. A single coat is absorbed unevenly, lets the background show through and reveals patchy areas under the raking light from a window.

Situation	Typical coats
Refresh in the same colour, sound surface	Often 2 finish coats, sometimes 1 if the surface is perfect
New surface (plaster, plasterboard)	Primer + 2 finish coats
Marked colour change	Primer + 2 finish coats, sometimes 3
Dark to light	Tinted primer + extra coats
Bright or saturated shade	Suitable primer + 2 to 3 finish coats

Bright shades (red, yellow, some blues) and going from a dark wall to a light one are the cases where you add coats: their pigment covers less, and the contrast with the background requires a tinted primer to avoid multiplying passes. The exact number is decided after examining the surface during the quote visit, not by guesswork.

Drying in three stages: do not confuse dry with hard

Is it dry? has no single answer, because paint goes through three quite distinct stages. Confusing them leads to nasty surprises.

Stage	Indicative time (water-based acrylic)	What you can do
Touch-dry	About 1 to 2 hours	The finger no longer marks the surface
Recoatable	Several hours, per the data sheet	Apply the next coat
Fully cured (hard)	Several days to weeks	Wash, scrub, put the film under stress

Touch-dry only means the surface no longer feels sticky: the film is still soft underneath. The recoat time is the one to respect between two coats; applying too soon makes the paint blister or pull the coat beneath. Full cure is the longest stage: only then does the paint reach its full hardness and its resistance to washing.

These times are relative physical benchmarks, not a work schedule. They depend on the product, and always on the manufacturer’s technical data sheet. A cold, closed-up studio in Eaux-Vives in winter will dry more slowly than a mild, ventilated flat; humidity and temperature govern the whole process.

Why cold and damp change everything

Water-based paint dries by evaporation, then by the film forming. Two factors govern the speed: temperature and humidity (the moisture in the air).

In a cold room — a ground-floor flat on a courtyard in Plainpalais, a cellar, an empty home left unheated in winter — evaporation slows and all the times lengthen. Air saturated with moisture has the same effect: the water in the paint struggles to leave. This is especially true in rooms with no ventilation and in areas already prone to condensation, such as a poorly aired bathroom.

Conversely, a mild temperature and renewed air speed up the set. Hence the importance of ventilating during and after application: it clears both the moisture and the volatile compounds. This is also why any stated time stays cautious and conditional — we speak of a few hours or several days, never a guaranteed schedule.

Smell: what is normal, what to avoid

The smell of paint often worries people, especially in an occupied home or with young children. Here again, the facts are simple.

Water-based acrylic paints, low in VOC emissions, give off a faint smell that generally fades within one to two days with good ventilation. VOCs — volatile organic compounds — are the substances that evaporate from the film as it dries; the less a paint emits, the healthier the indoor air stays and the more discreet the smell. This is the decisive criterion for a child’s room or a sensitive person. The subject is covered in our page on eco-friendly, low-VOC paint.

Solvent-based (alkyd) paints, on the other hand, are best avoided in an occupied interior: they smell stronger and take longer to clear. A residual smell that lingers for several days despite ventilation is worth checking against the product used and the room’s airflow. So “odourless” should be qualified: the aim is a clearly improved olfactory comfort, not a total absence.

Furniture, frames, reoccupying: patience pays off

This is the most common mistake: putting everything back as soon as the surface stops feeling sticky. But touch-dry does not mean hard. The film keeps hardening for several days, and it is during this phase that it is most vulnerable.

Three simple habits prevent damage:

• Do not push furniture against freshly painted walls too soon: contact can mark or stick to the still-soft film, especially on a satin or enamel finish.
• Wait before rehanging frames, shelves and hooks: an early pressure point or rub will pull the paint off.
• Space out the coats as per the technical data sheet, without rushing the work to “finish the same evening”.

On heavily used areas — skirting boards, frames, the enamel finishes on doors and radiators, hallway walls — wait longer before any contact or cleaning, as full hardness takes the longest to develop. The technical terms used here (primer, coverage, full cure, VOC) are defined in the painting glossary.

These benchmarks are physical facts, not a project duration. The actual course of the work is defined on site, after examining the surface: that is the whole point of the quote visit, free and with no obligation. The work is covered by the 2-year legal warranty (Art. 371 CO).