Water dissolves soluble salts and calcium hydroxide inside the concrete, carries them to the surface and evaporates, leaving a white bloom that reacts with air to form calcium carbonate. It shows up most on walls, basements and new slabs in cool, damp weather and is usually cosmetic. Dry brushing removes fresh deposits, while a hard crust needs a mild acid wash and a fix for the water source.
Basement wall's covered in efflorescence along the cold joint, so that's where your water is coming in.
Efflorescence on a basement wall is a moisture map: wherever it collects, water is moving through the concrete.
Also heard as
- bloom
- lime bloom
- whitening
Related terms
Cold joint
An unplanned seam left where fresh concrete was placed against concrete that had already begun to set.
Curing
Keeping fresh concrete moist and warm enough, for long enough, that the cement keeps hydrating.
ASR
Alkali-silica reaction, a slow internal reaction between cement alkalis and certain aggregates that cracks concrete.