Staining and discolouration on plaster walls and ceilings is almost always a symptom of moisture, rather than a surface problem. Painting over stains without finding the cause is a waste of money — the stains will bleed through.
Types of Plaster Staining and What They Mean
| Stain type | Likely cause |
|---|---|
| Yellow or brown patches | Water ingress — roof leak, plumbing leak |
| Tide marks (horizontal lines) | Past water leak that has dried out |
| White powdery deposits | Salt efflorescence from rising damp or mineral salts |
| Dark patches on external walls | Penetrating damp through masonry |
| Black speckling | Condensation and mould growth |
| Pink or red staining | Tannins from timber behind the plaster |
Can Stains Be Sealed Before Replastering?
Yes — once the source of damp is fixed and the wall has dried, stain-blocking primer (shellac-based products like Zinsser BIN are most effective) can be used to isolate water stains before plastering or painting. Do not use standard emulsion primer to seal water stains; it will not prevent bleed-through.
When Should Stained Plaster Be Replaced?
If the plaster has been saturated and has softened, crumbled or blown — or if salt deposits have damaged the plaster matrix — replastering is necessary. Painting or sealing damaged plaster will not restore its structure.
Get Quotes for Staining Assessment and Replastering
A qualified plasterer will assess whether stained areas need replastering or just treatment. Get 3 free local quotes.