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Step by step
How to plaster a wall: preparation to finish
Plastering looks like magic in skilled hands, but the basics can be learned. This guide covers interior gypsum and lime plastering on a small wall, from bare surface to a smooth finish.
1. Choose the right plaster
Gypsum plasters are used indoors and set in about an hour or two; base coats are usually 8–15 mm thick and finish coats 2–3 mm. Lime plasters are softer, more breathable and suit old solid walls. Cement renders are for outside walls. The Plaster calculator estimates the bags you need from area and thickness.
2. Prepare the wall
Remove loose material, dust and grease. Treat the suction of the background: very absorbent surfaces such as brick or old plaster are dampened or primed, smooth or dense surfaces such as concrete need a bonding primer. Fit metal or plastic beads on external corners and around openings to give straight, strong edges.
3. Mix in clean buckets
Add plaster to the water, never the other way round, and mix with a paddle until smooth and lump-free. Use clean water and clean buckets: residue from a previous mix speeds up setting. Mix only what you can apply before it starts to stiffen.
4. Apply and flatten
Load the hawk, apply plaster with the trowel in upward sweeps, starting at the bottom corner. Spread to an even thickness, then rule it flat with a straightedge (a feather edge or darby), filling hollows and taking off high spots. Keep the edges of the working area wet so the next section blends in.
5. Trowel to a smooth finish
As the plaster firms up, trowel it again with light pressure and a little water, holding the blade at a shallow angle. Two or three passes give a smooth surface. Do not overwork it, which brings water to the surface and weakens the finish.
6. Let it dry properly
New plaster must dry completely before painting, often a week or more depending on thickness and ventilation. Ventilate, but avoid rapid drying with heaters. Prime with a mist coat (diluted emulsion) before the finish paint. See How to paint a wall: a step-by-step guide.
Common mistakes
- Skipping the suction treatment, so the plaster dries too fast and cracks.
- Mixing in dirty buckets, which makes the plaster set early.
- Applying too thick in one coat.
- Overworking the surface with too much water.
- Painting before the plaster is fully dry.
Frequently asked questions
How long does plaster take to dry?
Gypsum skim usually takes several days; thicker base coats can take a week or more.
How thick should plaster be?
Base coats about 8–15 mm and finish coats about 2–3 mm for gypsum; follow the product's limits.
Can I plaster over painted walls?
Yes, with a suitable bonding primer, if the paint is sound.
What is a mist coat?
A first coat of emulsion thinned with water, used to seal fresh plaster.
Lime or gypsum?
Gypsum for most modern interiors; lime for old solid walls that need to breathe.