The Stain Library

Material

Bare plaster

A highly absorbent unsealed surface that cannot be washed, where the accepted repair is to dry it, seal the stain and paint over it.

  • SurfacePorous
  • WashingSpot only
  • Colour run riskHigh
  • Reviewed7 September 2026

What bare plaster can and cannot take

  • Heat Avoid
  • Water and soaking Avoid
  • Acids, including vinegar Avoid
  • Strong alkalis Avoid
  • Solvents Avoid
  • Chlorine bleach Avoid
  • Abrasives Avoid

Always test on a hidden area first and let it dry before you treat the visible mark.

General rules for bare plaster

There is no cleaning method here, and saying so is the useful part.

Get the solids off, blot without pressing, and let the wall dry completely. Wetting bare plaster to clean it makes the stain larger and adds a water mark of its own.

When it is dry, the repair is a white pigmented shellac primer over the stain and then paint. The conservation guidance is specific that a stain will bleed through ordinary paint unless it is sealed first.

Check the label

Bare plaster is one of the most absorbent surfaces in a house and it cannot be cleaned. Anything liquid goes straight in, and building conservation practice is not to try to wash a stain out but to dry the area, seal it with a stain blocking primer and paint over it.

Stains on bare plaster

Bare plaster is unsealed gypsum, and it drinks.

It cannot be cleaned

Liquid is absorbed within seconds and there is no way to draw it back out of a vertical surface. Every attempt to wash it spreads the mark and adds a tide line.

Stains bleed through paint

Conservation practice notes that a stain in plaster will come through finish coats of paint unless it is blocked. That is why painting over a mark usually means painting it twice.

Shellac is the standard block

A white pigmented shellac primer seals and blocks a stain so it cannot bleed. It is sold for exactly this and it is inexpensive.

Prime the whole wall

The same guidance warns that spot priming leaves visible shiny patches under standard paint, so the wall rather than the patch is the unit of repair.

Sources

What we checked and when. Where a manufacturer instruction disagrees with anything here, follow the manufacturer.

  1. Concealing water stains on plaster surfaces, US General Services Administration authority

    Building conservation procedure establishing that stains in plaster bleed through finish layers of paint if they are not sealed, that the moisture source must be found and the surface allowed to dry completely first, that the area is cleaned with a stiff brush and a damp cloth, that a white pigmented shellac is used to seal, prime and block the stain, and that the whole wall is primed rather than only the stained patch when a standard paint is used, to avoid visible shiny patches.

    Checked 7 September 2026

  2. Dulux Easycare frequently asked questions, Dulux manufacturer

    Paint manufacturer guidance that its washable matt uses a stain repellent technology which makes spills bead rather than absorb, that a mark is cleaned with a soft non abrasive damp cloth, that a stubborn stain is treated with a non bleach based cleaner such as washing up liquid on a soft damp cloth, that abrasive cloths and scrubbing are avoided, that spills are best dealt with quickly, and that the stain repellent property returns once the paint is fully dry again.

    Checked 7 September 2026

  3. How to clean wallpaper, William Morris Wallpaper specialist

    Wallpaper guidance that vinyl faced papers resist moisture, soap and gentle wiping while traditional paper, grasscloth, fabric and bamboo do not, that cloths must be wrung thoroughly because damp rather than wet is the rule, that wallpaper paste is activated by water so excess water at a seam breaks the bond and lifts the paper, that surfaces tolerate gentle wiping but not abrasive scrubbing, that cleaning is done downwards to avoid drip marks, and that the area is dried immediately.

    Checked 7 September 2026