Freshly plastered walls look ready long before they actually are, and painting too soon is one of the most common ways a good plastering job gets spoiled. As a rough guide, a skim coat needs around a week to dry and full replastering can need a month or more. Here is what actually affects those timescales, and how to tell when your walls are genuinely ready for paint.
The honest answer is that it depends on what was plastered and how thick it is. A standard skim coat of multi-finish over existing plaster or plasterboard is usually dry enough to paint in 3 to 7 days in warm, well ventilated conditions. If a room has been fully replastered with a backing coat such as bonding or hardwall plus a skim, you are looking at 2 to 4 weeks, and sometimes longer in winter.
The colour tells you most of what you need to know. Fresh plaster starts a deep terracotta pink or brownish grey and dries to a pale, even, light pink across the whole surface. If you can still see darker patches, usually around corners, window reveals and external walls, moisture is still working its way out and the wall is not ready.
Much of the housing stock around Liverpool is Victorian and Edwardian terraced property with solid brick walls and no cavity. Solid walls hold more moisture than modern insulated ones, so backing coats applied to bare brick dry noticeably slower, especially on north facing elevations that get little sun.
The North West climate does not help either. Damp autumns and winters keep indoor humidity high, which slows evaporation. A skim coat that dries in four days during a warm June can easily take ten days or more in a cold terrace in January. If a wall was replastered after a damp problem or a leak, allow extra time on top, because the plaster is drying out alongside residual moisture in the masonry behind it.
The aim is steady, gentle drying. Open windows for a few hours a day and keep internal doors open so air can move through the room. Background heating at a normal room temperature of around 18 to 20 degrees is ideal.
What you should not do is blast the wall with heat. Pointing a fan heater at fresh plaster, or turning radiators up high directly beneath it, dries the surface faster than the material behind it and causes shrinkage cracks and a weakened finish. A dehumidifier running in the room is fine and genuinely useful in winter, just keep it a couple of metres back from the freshly plastered wall rather than aimed straight at it.
Even fully dried plaster should never be painted straight over with standard emulsion. New plaster is highly porous and will suck the moisture out of paint almost instantly, leaving patchy coverage and paint that can peel off in sheets later. The first coat needs to be a mist coat, which is a non vinyl matt emulsion watered down by roughly 20 to 30 percent, brushed or rolled on and left to dry fully.
Once the mist coat is on and dry, usually within 24 hours, you can apply your normal topcoats as usual. Avoid using vinyl silk or a bathroom paint as the first coat on bare plaster, as these seal the surface and stop any remaining moisture escaping, which can lead to blistering months down the line.