Why New Plaster Is Different

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Fresh plaster is highly porous. If you apply normal emulsion paint directly onto new plaster, the plaster absorbs the water content rapidly, the paint dries unevenly and can peel away from the wall. This is one of the most common — and costly — decorating mistakes.

What Is a Mist Coat?

A mist coat is a very diluted emulsion — typically 3 parts paint to 1 part water — applied to new plaster as a primer. Because it's much thinner than normal paint, it soaks into the plaster surface rather than sitting on top of it. As it dries, it seals the surface and gives the subsequent coats of paint something to bond to.

The Process: Step by Step

  1. Wait for the plaster to dry fully — new plaster must be completely dry before painting. This typically takes 4–6 weeks depending on thickness and room temperature. Fresh plaster is dark pink/brown; fully dry plaster is uniformly light pink/cream. Don't rush this step.
  2. Apply the mist coat — use a cheap emulsion (the mist coat will be fully covered anyway). Dilute 3:1 paint-to-water and apply with a roller. It will look patchy and uneven — this is normal.
  3. Allow to dry completely — usually overnight minimum.
  4. Apply 2 coats of standard emulsion — undiluted, in your chosen colour and finish.

Can You Use a Commercial Primer Instead?

Yes — there are purpose-made plaster primers/sealers (such as Dulux Trade Plaster Sealer) that can replace the mist coat. These are slightly more expensive but can be more consistent than mixing your own diluted emulsion.

Signs You've Skipped the Mist Coat

  • Paint peeling away from the wall within weeks
  • Paint "rolling off" during application — sitting on the surface rather than soaking in
  • Uneven colour and patchy coverage even with multiple coats

What Your Decorator Should Do

Any professional decorator should automatically include a mist coat when working on new plaster. If you're getting quotes, ask specifically whether a mist coat is included if you have any recently plastered walls. It adds a day to the job but is non-negotiable for a good finish.

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