In short
A normal skim in a warm, ventilated room is usually ready for a mist coat after five to seven days, which is what we tell customers on every job. Dulux say plaster can take up to four weeks to dry out completely, and a thick undercoat on a solid wall is at that end. Wait until the whole surface has turned an even pale pink with no dark patches, then paint with a watered-down emulsion first.
This is a job for our Plastering service.
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What dry actually means
Plaster sets in a couple of hours; that is the chemical reaction. Drying is the water leaving the wall, and that takes days or weeks. A skim on plasterboard dries fast because there is nowhere for water to hide. A full two-coat job on a solid brick wall, or a patch where we had to take it back to bare masonry, holds far more water and takes correspondingly longer.
Dulux's guidance is that plaster can take up to four weeks to dry completely. On our jobs a normal skim in a heated room is usually ready to mist coat in five to seven days, and we say so when we leave. The wall tells you: it goes from dark brown to an even pale pink as it dries. Dark patches mean it is still wet there, usually around windows and in corners. Wait for them.
What speeds it up and what does not
| Do | Avoid |
|---|---|
| Keep the heating on low and steady | Blasting a fan heater at one wall, which dries the surface and cracks it |
| Open a window a little for ventilation | Shutting the room up with no airflow |
| Run a dehumidifier in a damp season | Painting over dark patches because the rest looks dry |
| Leave a thick undercoat longer than a thin skim | Hanging wallpaper straight onto bare plaster |
Winter jobs in older houses around Eye, Stowmarket and Ipswich take the longest. A solid wall in an unheated room in January can still be showing damp patches after a fortnight. That is normal; it is not a fault with the plaster.
How to paint new plaster
- Mist coat first. New plaster is thirsty. Dilute a plain matt emulsion with water (Dulux suggest about ten parts paint to one part water) and roll it on. It soaks in and gives the top coats something to grip.
- Let the mist coat dry before the first full coat.
- Use a breathable paint. Vinyl silk, bathroom paints and any one-coat product straight onto new plaster will peel in sheets, because the plaster is still giving off moisture behind them.
- Two top coats after that, as normal.
What if you have to decorate sooner?
Sometimes a tenant is moving in or the carpet is booked. Tell us before we start. On plasterboard we can tape and joint rather than skim, which dries far faster, and on a full re-plaster we can plan the drying-out into the programme so nothing is painted wet. What we will not do is tell you it is fine to paint a wall that is still dark in the corners.