Efflorescence on polished concrete is white, powdery and returns after cleaning. That return is the diagnosis: salt is being carried to the surface by water, and removing the salt without removing the water only restarts the cycle.

Identify before treating

Appearance	Likely cause
White powder, reappears monthly	Moisture moving through the slab
Hard white crust at joints	Water at joint or edge, often from below
Grey haze, no powder	Densifier residue, not efflorescence
Localised bloom near a wall	Leak, downpipe or irrigation

Test with a drop of water: efflorescence softens and dissolves, densifier residue does not. This one test prevents a pointless acid wash.

Removal that does not damage the polish

1. Dry brush first; removing salt dry avoids driving it into pores.
2. Wipe with clean water and a microfiber, changing water often.
3. For hard crust, use a diluted mild acid only on the crust, neutralise within minutes, and rinse thoroughly.
4. Buff dry afterwards to restore sheen.

Never acid wash a whole polished floor. It opens the densified layer and the area will re-haze within weeks.

Stop the source

• Test slab moisture with a plastic sheet or calcium chloride test.
• Check joints, penetrations and wall bases for water entry.
• Confirm drainage slopes away from the slab, including downpipes.
• If moisture is ongoing, specify a breathable treatment rather than a sealer that traps it.

Prevention in new work

Do not densify or seal a slab that is still releasing moisture. Efflorescence under a sealer becomes a trapped salt layer that blisters the film. Cure time, not calendar time, decides readiness.

If the bloom returns twice after correct removal, stop cleaning and start a moisture investigation. The white powder is the symptom; water is the problem.