efflorescence

Efflorescence is the appearance of a white, powdery, or crystalline deposit on the surface of porous materials. It results from soluble salts within the material or in nearby sources being dissolved by moisture, carried to the surface through capillary action, and then crystallizing as the water evaporates.

Common environments include masonry, concrete, brick, stucco, plaster, limestone, sandstone, terra-cotta, ceramic tiles, and other cement-based products. It often occurs after rain, during periods of high humidity, or where there is ongoing moisture movement through the material.

The formation process involves water dissolving salts in the material or the surrounding environment, transporting these salts to the surface, and leaving crystalline residues once the water evaporates. The salts may originate from sulfates, chlorides, nitrates, carbonates, or other soluble salts present in the material, in the mortar joints, or in the soil and groundwater adjacent to the structure.

Efflorescence is typically cosmetic, but crystallization can cause surface scaling or spalling in some cases, especially with repeated cycles of wetting and drying. It can also indicate excess moisture, which, if unaddressed, may contribute to longer-term deterioration of porous substrates.

Prevention and management focus on reducing moisture movement and choosing compatible materials. This includes improving drainage, fixing leaks, using breathable, lime- or cement-based mortars, and avoiding non-breathable sealants that trap moisture. Cleaning methods range from dry brushing to gentle washing with water; aggressive acids should be avoided as they can damage the substrate. If efflorescence recurs, professionals may investigate the moisture source and salinity levels to determine appropriate remediation.