The impulse to decorate as soon as the builders have gone is completely understandable. You've lived with dust and disruption and now you want your house back. But decorating too soon after plastering or screeding is one of the most common and most avoidable mistakes in any renovation. Paint applied to damp plaster traps moisture, causes bubbling, and will need to be stripped and redone within a year. The patience required at this stage saves significant cost and frustration later.
Drying Times: What You're Actually Waiting For
New plaster is substantially water: the plastering process uses large quantities of water which need to evaporate before the plaster is chemically stable enough to accept paint. How long that takes depends on the type of plaster, the thickness, the temperature, and the ventilation.
Gypsum skim plaster (the standard finish coat applied over plasterboard or browning coats) is typically 2-3mm thick. In good conditions (above 15°C, with ventilation), a skim coat takes 4-6 weeks to dry sufficiently for painting. Thicker browning coats take longer. A whole room of fresh skim in winter with poor ventilation can take 8-12 weeks.
Sand and cement screed (the common floor finish over underfloor heating or as a base for floor tiles) takes significantly longer. The rule of thumb is 1 week per 10mm of screed depth, up to 40mm, then longer for thicker applications. A standard 65mm screed over UFH takes a minimum of 6-7 weeks; 8-10 weeks is safer for a substrate that needs to be stable before tiling or laying engineered timber. Anhydrite (liquid) screed takes approximately 1 day per mm, so a 50mm anhydrite screed takes about 50 days minimum.
Rendering. External cement render takes 4-6 weeks before painting with a suitable masonry paint. Painting too early traps moisture and causes the render to blow (delaminate) or the paint to bubble and peel.
How do you know if plaster is dry enough? The colour is the best visual indicator: fresh plaster is dark and uniform; dry plaster is light and patchy. A moisture meter confirms it numerically. For painting, the moisture content should be below 12%; for floor finishes over screed, usually below 3-5% (check the flooring manufacturer's requirements).
The First Coat and What It Does
New plaster is very porous and alkaline. Applying full-strength vinyl emulsion to new plaster as a first coat seals the surface unevenly, produces a patchy finish, and makes it much harder to achieve a smooth, consistent top coat.
The correct approach is to apply a mist coat first: a highly diluted emulsion (approximately 50/50 paint to water, or a dedicated new plaster primer) that soaks into the plaster and provides a consistent base for subsequent coats. A mist coat seals the surface uniformly without trapping moisture, allowing the plaster to breathe as it completes drying. After the mist coat, two full-strength coats of emulsion will produce a stable, even finish.
Using white for the mist coat is conventional and makes it easy to see coverage. The mist coat doesn't need to be the final colour.
Surface Preparation
The quality of the finish is determined primarily by preparation, not by the quality of the paint. Good paint on a poorly prepared surface will look poor. Modest paint on a well-prepared surface will look good.
Fill and sand. Even good plastering leaves minor imperfections: small holes, scratches, and the occasional shallow depression where the skim has pulled back slightly. These are filled with a fine surface filler (Polyfilla or Toupret Finishing are both good), allowed to dry, and sanded back with a fine-grit (180-240 grit) paper. For large areas of minor imperfection, a flexible filler applied with a wide blade and feathered out provides a smooth surface efficiently.
Joints in plasterboard. Where sheets of plasterboard meet, the joint needs to be taped and filled before skimming or before painting on a dry-lined finish. If the skim coat has pulled back at a joint, there's a natural weakness there. Fill, sand, and apply a coat of diluted PVA before the mist coat.
Woodwork preparation. New timber (skirting boards, architraves, door frames) needs to be primed before painting. Previously painted woodwork needs to be lightly sanded to provide a key for the new paint. Fill any nail holes and imperfections in the timber with wood filler. Caulk the joint between skirting and wall (not paint it over: caulk accommodates the movement between wall and timber, paint doesn't).
Ceilings. Ceilings in new extensions often have thermal movement as the building settles and the materials adjust to temperature cycling. Hairline cracks at the junctions of ceiling sheets are common and can be filled and taped with paper tape before painting.
Sequencing the Decoration
The conventional order of decoration in a room: ceilings first, walls second, woodwork last. This minimises the risk of getting ceiling paint on walls you've already finished, and wall paint on skirtings you've painted. In practice, most decorators cut in and roll one surface at a time, and the exact sequence is less critical than being systematic and protecting what's already done.
Floor finishes go in last, after all painting is complete (including skirting). Fitting carpet before painting is a reasonable way to protect fresh carpet during painting provided you have good dust sheets and care; laying engineered wood or LVT before the last coat of paint is not recommended as paint spills and abrasion from ladders and equipment will damage it.
The final decoration is often best done before furniture arrives. You can cut in at ceiling height, work freely around the room, and leave no area inaccessible. Once the room is furnished, touching up is laborious. Do it all in one pass before the room is in use.
Shrinkage Cracks: What's Normal
New plaster cracks. It's a normal consequence of the drying process: fine hairline cracks appear as the plaster shrinks slightly, particularly at corners, door openings, and the junctions of new and old plasterwork. These are surface-level and not structural.
Wait until the plaster is fully dry before filling shrinkage cracks. Filling while the plaster is still drying means the crack may reopen; filling after full drying means the fill is stable. One filling and decoration pass is better than two.
Cracks that are wider than 2mm, that occur at the junction of old and new masonry, or that appear consistently along the same line (suggesting differential movement rather than simple shrinkage) should be noted and monitored. Genuinely structural cracks are usually distinguishable from shrinkage by their pattern and location, but if you're uncertain, have them assessed.