If exterior areas of your home are in the shade and hold moisture, they can develop unsightly green algae. The length of time the algae has been on the siding determines how difficult it will be to remove the algae. Normal cleaning with laundry or dishwashing detergent can remove new algae formation, but it's necessary to use a stronger cleaner and method of cleaning for older algae.
Oxygen Bleach Cleaner
You can use an oxygen bleach cleaning solution on vinyl, wood or aluminum siding without affecting the finish. Oxygen bleach also offers an environmental bonus because it will not damage plants or grass or create instabilities in soil. According to The Natural Handyman, a proper mixture of cleaning solution consists of 8 oz. of oxygen bleach mixed well in a gallon of warm water.
The easiest method of applying the bleach solution to the siding is using a hand sprayer. You can either purchase a hand-pump sprayer to use along with a gallon-size bucket or use a self-contained sprayer, like those used to apply week killer, to spray the cleaner on the siding. Allow the solution to sit on the siding for up to 20 minutes but do not allow the solution to dry on the siding. Scrub the siding with a long-handled scrub brush or push broom to remove the algae, and then rinse the siding thoroughly with cool water.
Trisodium Phosphate Cleaner
Trisodium phosphate, or TSP, once was an ingredient in household items, such as laundry and dishwashing detergents. In the early 1970s, several states placed limitations on phosphate usage because of the agent's e negative environmental effects. Construction workers still use TSP because it can completely remove mold, mildew, algae, dirt, grease and grime from many surfaces, leaving them clean for repair or refinishing.
The TSP mixing ratio will vary based on the manufacturer and the level of strength you require, but a common mixing ratio for heavy cleaning is 1/2 cup of TSP mixed with 2 gallons of warm water. Because TSP can discolor painted surfaces, wood and metal, test the cleaner on a small area of wood or aluminum siding. Before you apply the cleaner to the siding, mask adjoining painted areas to protect the paint.
To limit the effect of TSP on nearby plants, soak the plants and the surrounding ground prior to applying the TSP solution to the siding. If only a few areas of siding have a concentration of algae, clean the areas by hand rather than spraying the solution so you to limit the TSP’s area of coverage. Once you’ve applied the cleaner to the siding, scrub the siding with a push broom or long-handled brush to remove the algae, and then rinse the siding thoroughly. Always wear gloves when you work with TSP.
Pressure washing can remove dirt and grime from siding, or you can combine pressure washing with the use of a cleaning agent. The biggest mistake most homeowners make when pressure washing is improperly using the pressure washer, causing damage to the siding and creating leaks. A pressure washer comes with tips in varying degrees that control the concentration of spray. Jon Tobey, with Fine Homebuilding, recommends a 15-degree tip for pressure-washing siding. Use a ladder to get even with or above the area you want to wash, and start pressure-washing from the top down. You should never spray water up at the siding, or you may force water underneath the siding and cause damage. Wear safety glasses or another form of eye protection when working with a pressure washer.