How to Clean Stains Off Stucco

"Stuck on stucco" would be an easy play on words for talking about stucco stains, but it isn't really accurate. Stains on stucco are most often, really, stains in the stucco. Stucco improves the look of some cheaper stonework while it also acts as an insulator: It's attractive and eco-friendly. Two of the down sides of stucco are its porosity, which makes it easier for stains to set in, and its sometimes crumbly fragility. It can wear down and chunk off so stains and discoloration appear darker and deeper at various points of the surface.

Stucco is a mixture of concrete, fine sand and lime -- a powdered stone material -- that is applied wet over stone, brick or concrete walls, or layered on wooden or metal frames and meshwork. Some modern applications of stucco are strengthened with acrylics or synthetic binding agents over foam insulation, but more traditional stucco is simply three dry ingredients and water mixed, applied to surfaces and left to harden and dry.

Mold, dirt and chemical reactions from hard water or other acid or mineral exposure might require some maintenance and TLC, but for the most part, cleaning stains off of stucco is a gentle and straightforward bit of upkeep.

Next we'll look at how to enjoy the green benefits of stucco without the green and brown tinge of mold, minerals, dirt and leafy markings.

Removing Hard Water Stains from Stucco

One sneaky but common type of stucco stain comes from something clear that's also used to treat stains: water. Depending on geography, many homes have hard, mineral-rich water running through their pipes that stains their porcelain tubs, toilets and sinks. This same water can stain stucco, which has a porous texture similar to hard surfaces used for kitchen and bathroom fixtures.

But how does the water from the plumbing effect the outside of a house? It comes from the water hose and from drain pipes used for overflow because the rain water mixes with the ground water of sprinkler systems and garden hoses. Stains come up through the soil and penetrate the lower stucco walls, and sections of walls hosed off with piped water can develop staining -- ironically, from repeated cleanings.

One of the most effective ways to clean hard water stains is also ironic: gentle water pressure can remove hard water stains. Pressure-washing with too much pressure, on the other hand, can damage stucco surfaces by removing too much of the outer layer and creating more rough and porous areas where stains can set in and build up.

Not all methods of stucco stain removal are all wet, though.

Methods and Materials for Cleaning Stucco

Other sources of stucco stains, ranging from mold, soot and paint to vining plants, grasses and shrubs, can be removed with one or a combination of several methods:

chemically -- with specialized cleaning agents for stone, lime, cement and stucco or with diluted bleach (if tolerated in a sample test of the area to be cleaned)
with water pressure -- using even spraying with a home garden hose and attachment or with a higher-pressure spray system
mechanically -- with brushes and sandpaper or other abrasives and muscle power, detergents and sponges

Whether using a wet or dry method, stucco cleaning should most often be a gentle process. Saturating or pre-wetting stained areas with water will help to draw stains to the surface, and once the pores are full and discoloration is closer to the top, removing problem areas usually won't involve getting rough with the stucco and damaging the surface.

Other than being careful not to rough up or compromise the outer stucco layers and designs, another concern is protecting the ground around the wall or spot being cleaned so chemicals and particles of lime, concrete or acrylics don't flow into the soil and drainage areas.

If approaching clean-up of historic stucco with the added wear-and-tear of age, it also may be best to consult a professional building restoration consultant or preservationist before getting started.

Whatever the stucco stain, you don't have to be stuck living with it.

Lots More Information

Sources

City of Fort Lauderdale. "Historic Preservation Design Guidelines: Masonry, Stucco and Concrete." ci.ftlaud.fl.us. May 1, 2012. (June 9, 2012) http://ci.ftlaud.fl.us/planning_zoning/historic_preservation/pdf/guidelines/masonry_stucco.pdf
Clark, Jim. "Stained Stucco." ThisOldHouse.com. 2012. (June 6, 2012) http://www.thisoldhouse.com/toh/asktoh/question/0,,350009,00.html
Encyclopaedia Britannica. "Stuccowork." 2012. (June 10, 2012) http://www.britannica.com/EBchecked/topic/569846/stuccowork
Grimmer, Anne. "Preservation Brief 22: The Preservation and Repair of Historic Stucco." National Park Service, NPS.gov. October 1990. (June 7, 2012) http://www.nps.gov/hps/tps/briefs/brief22.htm
Portland Cement Association. "Stucco: FAQs." Cement.org. 2012. (June 7, 2012) http://www.cement.org/stucco/faq_cleaning.asp
State Historical Society of Iowa and National Park Service. "Cleaning Historic Stucco." IowaHistory.org. 2012. (June 6, 2012) http://www.thisoldhouse.com/toh/asktoh/question/0,,350009,00.html