What Causes House Stucco Paint to Stain?

Stucco Construction

• The process of adding stucco to concrete or cement walls typically involves spreading the liquid stucco on the walls in decorative days. Once the stucco dries, it forms a firm and hard texture. In some cases, the process involves embedding stucco nails or stucco wire onto the walls underneath and adhering the stucco to those construction elements. Moisture from rain or house leaks drips behind the stucco and causes rusting of the construction pieces. The rust touches the back of the stucco and, when it becomes visible on the exterior side, the stains are dark red, brown or even black.

Moisture Damage

• Even if you have stucco applied directly to concrete or cement, you may still have problems due to moisture damage. Stucco is not a permanent decorative item and does peel away from the concrete behind. Moisture soaks behind the stucco, reaching the concrete. As the concrete develops mildew or mold, the mold stains appear through the stucco. Depending on the type of mold or mildew damage you have and the color of your stucco, the stain may appear green, brown or black.

Dirt Stains

• Stains on the surface of the stucco that appear dark brown or black are likely caused by dirt and debris building up on the stucco. Stucco on your foundation may come about because of vehicles throwing dirt, mud and dust onto the stucco. Vegetation growing in the surrounding area may also cause the buildup of debris. Any plants, bushes or shrubs touching the stucco can leave behind dirt and dust. Even if you have vegetation growing near the stucco, animals and people can transfer the dirt onto the stucco.

Soot and Ash

• Dark stains on the stucco may come from grills placed near the stucco. Charcoal grills give off ash and soot during the cooking process and the soot may travel through the air and settle on the stucco. You should also beware of chimneys, especially if you have stucco on the second floor. Any soot that the chimney gives off can settle and build up on the stucco.