Why is my gloss paint still soft and tacky weeks later?

Water-based paint dries: the water leaves and the film coalesces. Solvent-based paint does something different — the solvent leaves quickly, and then the oil in the binder reacts with oxygen from the air over days and weeks to form a hard film. Anything that interferes with that reaction leaves you with a surface that is touch-dry but soft, marks with a fingernail, and picks up dust and fingerprints indefinitely.

What you'll need

• Warmth and ventilation — a fan and a heater if needed
• A scraper and chemical stripper, if it has to come off
• Talcum powder, as a temporary measure on a surface in use
• White spirit and cloths

Step by step

1. Check the conditions the paint has been curing in.Cold and damp are the commonest cause by a wide margin. Oxidative curing slows dramatically as temperature drops and stalls in a cold, unheated room. So does still air — the reaction needs oxygen, and a sealed room with no movement supplies it slowly.
2. Check how thick you put it on.Oxygen has to reach through the film. A heavy coat skins on the surface and the material underneath then cures extremely slowly or not at all, which is why the surface feels dry and the film beneath stays soft. This is the second most common cause and it is entirely self-inflicted.
3. Check what was underneath.Silicone from polish or sealant, wax, grease, an incompatible undercoat, or a coat applied over a stain block or shellac that was not fully dry can all interfere with the cure. So can painting over a bituminous or resinous surface.
4. Check the age of the tin.Solvent-based paint that has been open, part-used and stored for years can partially oxidise in the tin, and what remains cures unpredictably. Paint from a tin with a heavy skin and a thickened body is a prime suspect.
5. Give it warmth and moving air first.Before doing anything drastic, put heat and ventilation on it: warm the room to a normal comfortable temperature and keep gentle air moving across the surface for several days. A large proportion of tacky gloss cures out with nothing more than this, and it costs you only patience.
6. Test with a fingernail after a week of good conditions.Press a nail into an inconspicuous area. If it leaves no mark, it has cured. If it still dents easily and the paint moves under the nail, the film is not going to harden and it has to come off.
7. Remove it if it will not cure.There is no additive or topcoat that hardens a stalled oil film — putting another coat over it traps the soft layer permanently. Strip it with a chemical stripper appropriate to the paint, clean the surface thoroughly with white spirit to remove any contamination, prime, and start again in warmer conditions with thinner coats.

Tips

• As a stopgap on a door or a window that has to be used, dust the tacky surface lightly with talcum powder to stop it blocking against the frame. It is a temporary measure and not a cure.
• Traditional oil gloss simply takes longer than people expect even when everything is right — days to be handleable and weeks to reach full hardness. Read the tin's cure figure, not its touch-dry figure.
• If you have this problem repeatedly in a cold house, water-based satinwood and gloss are worth considering: they dry by coalescence and are far less sensitive to temperature.

Common mistakes

• Adding another coat to fix a tacky one — You seal the soft film underneath, which then cannot get oxygen at all. It stays soft permanently and now has a hard skin over it.
• Painting a coat on heavily to save doing a second one — Thick oil-based films cure from the surface inwards and can stay soft in the body indefinitely. Two thin coats always beat one thick one.
• Painting in an unheated room in winter with the windows shut — Cold slows the reaction and still air starves it. Both at once is the classic recipe for gloss that never hardens.

If it doesn't work

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