Exterior stucco is also known as Portland cement plaster, according to the Bob Vila Library. The material is porous and absorbs stains easily, such as bird droppings or mould and mildew. Cleaning stucco of dirt and dust is simple enough, but stains need deeper scrubbing and bleach products to remove them. Wash exterior stucco two to three times a year to keep the plaster from looking dull and drab.
Squirt two to three drops of dish detergent into a bucket of water and swish to create suds.
Spray the exterior stucco with a garden hose. Start spraying back and forth from the bottom of the stucco to the top. Spray one 12-foot section of stucco at a time.
Dip a scrub brush into the sudsy water and start scrubbing the wet stucco from the top, working your way down. Use a ladder to reach the top of the stucco wall.
Rinse the soap from the stucco walls with the garden hose, starting from the top, brushing side to side with the hose, and working down.
Mix a solution of one part bleach and nine parts water in a bucket and apply to any stains with a sponge. Rinse the bleach solution off the stucco with the garden hose after two to three minutes.
Move to the next section of stucco wall and repeat the cleaning process.
You may use a pressure washer instead of a garden hose on the stucco, but turn it to the lowest setting to avoid damaging the stucco surface. A garden hose is preferable.