Paint Peeling Off New Plaster After A Mist Coat

What's happening?

Rawlins Paints says the problem when a mist coat peels, goes powdery, patchy or bubbles is usually the same: the paint has not bonded to the new plaster, because it sat on the surface instead of soaking in. A mist coat is meant to soak into new plaster, reduce suction and leave a sound base for topcoats. It fails for five reasons Rawlins gives: the plaster was still drying, the wall was dusty, the paint was too thick, the wrong paint was used, such as a vinyl-heavy finish that dries too quickly on the surface, or the coat was overworked by rolling back over paint as it began to dry. Cold rooms, poor airflow and high moisture slow drying and can ruin a mist coat as well.

What usually causes it?

• Plaster that was still drying, shown by dark damp patches, when it was painted
• A wall left dusty, so the paint stuck to the dust and not the plaster
• A mist coat applied too thick, forming a weak film
• A vinyl-heavy or otherwise unsuitable paint on bare plaster
• Rolling back over the paint as it began to dry, lifting it
• A cold, damp or poorly ventilated room slowing the drying

Is it dangerous?

No. Damp that keeps returning after repainting is a different problem and may be a leak or ongoing moisture, so tell the plasterer or a damp specialist if patches stay dark.

Can I fix it myself?

Do not paint over peeling or bubbling areas. Scrape back to a sound edge, remove all the dust, let the plaster dry fully, then apply a properly diluted mist coat, following the paint maker's dilution. Rawlins says plaster should be fully pale with no dark damp patches left, usually after 3 to 7 days depending on the room, and that if the failure is widespread it is usually quicker and more reliable to start again.

When should you call a painter and decorator?

Call a painter and decorator if the failure is widespread or on a ceiling, or the wall will not stay sound. Call back the plasterer if the plaster itself is powdery or coming away, and a damp specialist if dark patches do not dry.

What will the painter and decorator actually do?

• Check the plaster is fully dry and sound before painting
• Scrape back failed paint to a firm edge and remove all dust
• Apply a correctly diluted mist coat suited to new plaster
• Let the mist coat dry, then apply the topcoats without overworking them
• Strip and repaint the whole area where the failure is widespread

Who fixes this

• Painting preparation
• Ceiling painting

Questions people ask

Sources & References

1. Rawlins Paints: why is my mist coat peeling or bubbling?
2. Dulux: 15 paint problems and how to fix them