An exclusion distance controls the efflorescence pattern distribution on porous media during salt solution evaporation

•Efflorescence patterns are observed on sintered copper wicks due to salt solution evaporation.•Salt crystals appear earlier and efflorescence spreads faster over wicks made of smaller particles.•Preferential efflorescence occurs over the smaller particles in wicks with a bimodal composition.•A scaling analysis provides a mechanistic explanation of the governing solute transport process.•An exclusion distance provides a guideline for designing porous media for efflorescence localization.