The Stain Library

How to remove baby sick from bare plaster

  • DifficultyProfessional
  • OutlookRarely removable
  • MaterialBare plaster
  • Reviewed7 September 2026

The short answer

Do not try to wash it. Bare plaster absorbs liquid within seconds and any attempt to clean it spreads the mark and adds a water ring of its own. Lift the solids, blot without pressing, and let the wall dry completely. The accepted repair is then to seal the stain with a white pigmented shellac primer and paint over it, priming the whole wall rather than only the patch.

If it has just happened

Blot without pressing and then stop. On bare plaster everything you do beyond that makes the mark bigger.

Heat can set this stain permanently

Do not use hot water, a tumble dryer, an iron or a steam cleaner until the mark has gone. Heat fixes this type of stain into the fibres and makes it far harder to shift.

Test on a hidden area first

Try any cleaner on a hidden part of the material first, such as a seam, an offcut, inside a hem or under a piece of furniture. Wait for it to dry and check for colour change before treating the visible mark.

Cleaning the mark is not the same as disinfecting

If the sickness came with a stomach bug rather than an ordinary posset, the surface may carry norovirus, which spreads easily and survives on hard surfaces. UK public health guidance is to wear gloves, avoid shaking contaminated laundry, wash affected laundry separately with normal powder at 60 C where the care label allows it, and disinfect compatible hard surfaces with a bleach based product afterwards. Do that after the stain work, not instead of it, and only where the material tolerates it.

Keep every kind of drying heat away until the mark has gone

Baby sick is mostly milk protein. Heat coagulates protein and locks it into the material, which is why a mark that would have washed out can become permanent after one hot wash, one pass with an iron, a hairdryer or a spell on a radiator. Cool or warm treatment, air drying, and a proper look in daylight before anything warm goes near it.

What you will need

  • Disposable gloves Sickness that came with a stomach bug is a hygiene job as well as a stain.
  • A plastic scraper or the flat of a knife For lifting solids off a wall without gouging the surface.
  • Several white cloths or sponges White, soft, and wrung out hard. Damp rather than wet is the rule on every wall surface.
  • Warm water Warm, not hot. Heat sets milk protein and softens wallpaper paste.
  • A dry towel For drying the area immediately, which matters more on a wall than almost anywhere.

Helpful but not essential

  • Washing up liquid A drop in the water. Paint makers specify a non bleach based cleaner such as this.

Fresh baby sick on bare plaster

Blot downwards, damp not wet, and dry it straight away.

  1. Lift the solids off first

    The flat of a knife or a plastic scraper, drawn downwards and away from the wall rather than pressed into it. Catch what falls with kitchen roll held below.

  2. Blot the run downwards

    Press a dry cloth onto the mark and lift. Work down the wall, because anything that runs lands on an area you are about to treat rather than on clean wall below.

  3. Then a barely damp cloth

    Wrung out hard. Damp rather than wet is the rule on every wall surface, painted or papered, and it is what stops a tide line forming.

  4. Dry the area immediately

    Blot dry and then leave the wall alone to dry out completely, which can take days on plaster. Nothing else helps until it is dry.

  • How longTen minutes
  • RepeatingBlot until nothing more transfers.
  • Stop ifnothing more transfers to a clean cloth and the wall has been dried

Dried baby sick on bare plaster

Softening and patience, and stopping before the surface burnishes.

  1. Brush or scrape the loose material away dry

    A soft brush or the flat of a blade takes off anything sitting proud, and it carries no risk of spreading the mark.

  2. Hold a damp cloth against it to soften

    A minute or two, without rubbing. Dried milk on a painted or papered surface softens and lifts rather than needing force.

  3. Wipe gently downwards, then dry

    Light pressure, one direction. Watch the surface as you go: if it starts to look shinier than the wall around it, stop, because that is burnishing and it is permanent.

  4. Feather the edge outwards

    Work the damp cloth outwards from the treated area so there is no hard boundary where the damp stopped.

  • How longTwenty minutes
  • RepeatingTwo gentle passes, then stop.
  • Stop ifthe mark has lifted, or two passes have not moved it and the surface is starting to shine

Old or set in baby sick on bare plaster

On a wall, the honest last step is usually paint rather than cleaner.

  1. Decide whether it is a stain or damage

    A mark that has not moved after two gentle passes is either in the surface or has burnished the area around it. More cleaning makes the second one worse.

  2. Let it dry completely and look again

    Walls look far worse damp, and a mark that seems obvious while wet is often invisible the next day in normal light.

  3. Seal before repainting, not after

    Building conservation practice is that a stain will bleed through fresh paint unless it is sealed first, and that a white pigmented shellac primer blocks it. Painting straight over a stain usually means painting it twice.

  4. Prime the whole wall, not the patch

    The same guidance notes that spot priming leaves visible shiny patches with standard paints. On a wall, the unit of repair is the wall.

  • How longAn hour, then a decision
  • RepeatingDo not keep working the same patch.
  • Stop ifthe mark has faded as far as it will, or the wall needs sealing and repainting

What not to use on bare plaster

  • Working upwards

    Water runs down a vertical surface and a drip onto dry wall below leaves a visible streak. Wallpaper guidance is specific about this: clean downwards so any run lands on an area you are about to treat.

  • Using a wet cloth rather than a damp one

    Excess water on a wall runs, soaks into plaster, activates wallpaper paste at the seams and leaves a tide line at the edge of the wet area. Wring the cloth until it is barely damp.

  • Scrubbing, or using an abrasive sponge

    Paint and wallpaper both burnish, which means the scrubbed area goes shinier than the surface around it. That shows in raking light and it is permanent short of repainting.

  • Bleach based cleaners

    Paint manufacturers specify a non bleach based cleaner. Bleach lightens paint colour unevenly and on wallpaper it strips the print.

  • Washing or sponging bare plaster

    It absorbs instantly, so washing spreads the stain over a larger area and adds a water ring at the edge of the damp patch. There is no cleaning method for bare plaster.

  • Painting straight over the mark

    Conservation guidance is that a stain bleeds through finish coats unless it is sealed first. Emulsion alone will not hold it back and the mark reappears within days.

White compared with coloured bare plaster

Plaster is pink or grey and any stain in it is visible from the moment it dries. It also comes back: conservation guidance is explicit that a stain will bleed through finish coats of paint if it is not sealed first, so an untreated mark reappears through the new emulsion within days. That is why the answer is a shellac based blocking primer rather than an extra coat.

If the mark is still there

Wait until the wall is completely dry, which on new or recently wetted plaster can take days. Nothing useful happens before that.

Then seal. A white pigmented shellac primer is the standard product for blocking a stain, it dries in under an hour and it stops the mark bleeding through whatever goes on top.

Prime and paint the whole wall between corners. Conservation guidance warns that spot priming leaves visible shiny patches under standard paints, so a sealed patch in the middle of a wall is usually replacing one visible mark with another.

When to stop and call someone

This is a decorating job rather than a cleaning one, and it is worth accepting that early. Once the wall is completely dry, seal the mark with a white pigmented shellac primer and repaint, priming the whole wall rather than the patch. If the plaster is new and still curing, wait until it has dried out fully before painting anything.

Why baby sick behaves this way on bare plaster

Bare plaster is unsealed gypsum, and it is one of the most absorbent surfaces in a house.

It cannot be washed

Liquid goes in immediately and there is no way to draw it back out of a vertical surface. Every wet attempt enlarges the mark and adds a tide line at the edge of the damp area.

Stains bleed through paint

Building conservation practice notes this directly, which is why painting over a mark on plaster so often means painting it twice.

Shellac blocks it

A white pigmented shellac primer seals, primes and blocks a stain in one product. It is inexpensive and it is the standard answer.

Prime the wall, not the patch

Spot priming shows under standard paint, so the wall is the unit of repair.

Sources

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

  1. 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

  2. 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

  3. 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

  4. How to remove baby formula stains, Purex Stain Lab manufacturer

    Manufacturer guidance identifying breast milk, formula and baby spit-up as protein stains, explaining the role of enzymes, and warning that the mark should be checked before any drying heat because heat sets what remains.

    Checked 7 September 2026