The first and foremost step requires to make a solution, which you would eventually use to clean the surface. The solution should consists of one gallon water along with 1 qt. chlorine bleach and one cup of trisodium phosphate. Stir the solution thoroughly, mix it using a wooden spoon or stick. Don't forget to take the necessary precaution measures by wearing rubber gloves.
Use the pump sprayer as prescribed by manufacturer's instruction. Do check if there's a malfunction or a leak in the sprayer beforehand, so that you don't face a problem once you're onto it.
Spray the surface with the homemade solution using the pump sprayer. The surface should be covered thoroughly with the solution. Make sure that the entire surface is covered with that solution. Use a ladder if necessary to reach up to high places. Mix more solution if required.
While spraying the nearby plants, you'll need to take some precautionary measures regarding the nearby plants. Spray the plants with clean water using a garden hose to ensure a good pressure and a considerable amount of water. In case of sensitive plants, use a plastic sheet or tarp to protect them beforehand spraying the cleaning solution.
Once you're done with the spraying, you'll have to brush the synthetic stucco next. Use a long-handled scrubbing brush for the purpose brushing the surface. Be gentle while brushing it, as you don't want it to wear off. It should be brushed from topped to bottom, and use a ladder where necessary.
Use a garden hose to apply high pressure of water over it, in order to cleanse it. Don't forget to rinse it thoroughly. The stucco should be rinsed by starting from top, followed by downward movements to remove the traces of the cleaning solution, leaving it cleansed.
Rinse any plants around the home with water from the garden hose, or remove the tarp or plastic sheets.