Coating defect

Efflorescence

White, crusty or fluffy salt deposits on concrete or masonry, often in bands along mortar joints.

Efflorescence: the surface as you see it, and a schematic cross-section.

Causes

Soluble salts in the concrete, water to dissolve them, and evaporation that brings them to the surface: all three are needed.
Water reaching the concrete from behind, from the ground below or through cracks and joints.

Prevention

Keep water out of the structure.
Let new concrete cure and dry before coating, and check for moisture first, for example with the plastic sheet test of ASTM D4263.

How it is assessed

Visual; find the source of the water before coating.

Telling it apart

Laitance: Laitance is a weak skin of cement and fines left by the casting, there from the start. Efflorescence is salt that water brings out later, and it comes back while the water keeps coming.
Chalking: On a coated wall, white powder can also be chalk from a weathered coating. Efflorescence comes from the concrete and pushes through or under the coating.

Repair

Stop the water, remove the salts by brushing or washing, rinse and let the surface dry before coating. Coating over efflorescence fails. The specification and the coating manufacturer have the final word on the repair procedure.

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About this page

Written from coating practice and the published rating standards, in our own words; the drawing is schematic. Checked on 2026-10-14; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.