If you've just had your walls plastered, you might be wondering how soon you can decorate. The safe answer is probably about 4 to 6 weeks but with good ventilation and heating, possibly less. This might seem rather long and unnecessary but there's good reason behind it. At the stage where the walls look and feel dry, there's usually still moisture trapped in the wall waiting to evaporate. Some paint can form a water resistant skin over the surface area, meaning that the moisture retreats into the wall, forming mould. The other thing which happens is the trapped moisture reacts with the salts in the wall masonry and causes efflorescence. This, of course, ruins any decoration. There are paints on the market especially designed to allow new plaster to breathe so as to cut down on the time between plastering and decorating. Bear in mind that the walls still have to be completely dry to the touch and visibly dry.
What a lot of people don't realise is the amount of water involved in the plastering process. This water penetrates the existing masonry during the plastering and then has to work it's way out once evaporation starts from the surface.
If you are considering having plastering done, we'd recommend allowing a couple of months before decorating. If it's just a skim coat, the drying time will be a lot less (Usually around 3 to 5 days), but err on the side of caution.
When the newly plastered walls are ready for painting, do bear in mind that new plaster is very porous and will soak up paint, causing patchy results. There are a number of ways to counteract this. You can dilute water based emulsion paint and use as a base coat or primer. You can use watered down PVA adhesive as a sealant or you can use specially manufactured new plaster paint.
If you take a little care with the preparation, there's nothing quite like a newly plastered room when it's been painted. After spending good money on a plasterer, there's nothing worse than ruining the finish with a hasty paint job.