How it forms
- Water enters through cracks, window frames, roofs or pipes
- It dissolves calcium hydroxide and similar compounds in cement
- As water evaporates, salts crystallise as white powder
- Paint and skim coats blister and peel
Why scraping alone fails
Step 1: Find the source
Step 2: Stop the water
- External cracks: exterior seal / waterproofing (often needs scaffolding)
- Windows: remove old sealant, clean dry, re-apply
- Bathroom membrane failure: strip tiles and redo (pro job)
- Pipe leaks: plumber replaces lines
- Roof: redo waterproofing (pro job)
Step 3: Let the wall dry
Step 4: Surface works (only after dry)
- Scrape loose paint and skim to sound substrate
- Wire-brush salt crystals
- Alkali-resistant / waterproof primer
- Waterproof skim in thin coats
- Paint only when fully dry