Those unsightly white marks are a mineral build-up called “efflorescence.”
Efflorescence forms when minerals like salt and lime, which are found in stucco, brick and concrete, leech to the surface. This happens when your walls get soaking wet and then dry out in the sun, like after a heavy rain or if water from your sprinklers repeatedly hits a wall.
You can usually wash the stain away with water and a stiff broom. If that doesn’t work, mix up a cleaning solution of one part vinegar to five parts water, and scrub it on with a stiff nylon brush. Rinse all of the vinegar solution off with water.
