A.Ron Webber ,a veteran plastering contractor in Orange, Calif., responds: I’d say you are dealing with efflorescence, which is caused by water from the soil wicking up into the stucco and then evaporating. Salts dissolved in the groundwater are left behind, resulting in a chalky residue and high alkalinity that can weaken the stucco and interfere with top-coat adhesion. To fix the problem, you have to manage the water. For example, grading should be adjusted so that water flows away from the house, and sprinklers should be relocated so they don’t spray on the walls.

Installing a weep screed around the bottom of the house a minimum 4 inches above grade (2 inches above paved surfaces) would also help to keep efflorescence at bay. To do this, you will have to remove all the stucco up to about a foot above grade, install the weep screed, install 60-minute — or better — building paper and lath, and patch in the...

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