Bathroom grout is one of the most mould-prone surfaces in any home — porous, constantly damp, and hard to fully dry between showers. Here’s why it happens and what actually deals with it.
Grout is porous by nature, which means moisture seeps below the surface rather than sitting on top of it. Combined with the warm, humid conditions typical in Sydney bathrooms, this creates ideal conditions for mould to take hold below the visible surface.
Household mould sprays can lighten surface staining but often don’t reach mould growing beneath the grout surface, which is why it tends to reappear within weeks of a DIY clean.
Professional tile and grout cleaning uses higher-pressure water combined with treatments designed to penetrate the porous grout surface, not just clean the top layer.
Sealing grout after a professional clean creates a barrier that makes it significantly harder for moisture and mould to penetrate again.
Persistent mould exposure can affect people with respiratory sensitivities — addressing ventilation alongside cleaning is worth considering.
No — sealing typically needs reapplication periodically, though this varies by product and conditions.
In most cases yes, though grout discoloured for years may improve significantly rather than return to brand-new.
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