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Home Care Library

Roof Gutters

The Home Wizard app calculates your ideal home care program to avoid problems with your Roof Gutters, but sometimes trouble can still occur. Here are answers to questions about roof gutter cleaning mildew.


What's the best way to clean green mildew/algae off white aluminum siding?


Dear Adam:

Regarding the best way to remove green algae or mildew from aluminum siding, the answer is that it depends on how long the algae or mildew has been on your siding.

If the algae/mildew has not been on the siding for very long, then hopefully you should be able to clean it off with just a solution of laundry or dishwashing detergent in water. You can apply this with the type of hand sprayer that attaches to a garden hose, or you can use a large pail and a long-handled soft-bristled brush. And you may want to use the brush anyway for more difficult spots.

However, if the algae/mildew has been on your aluminum siding for a while, it may not come off with simple detergent washing. If this is the case, then the next more aggressive step is to use an oxygen bleach cleaner (NOT household bleach). You will want to mix about 8 oz. of oxygen bleach in a gallon of warm water. Be sure to mix the solution well. Spray the cleaner on the siding, and allow the solution to sit on the siding for about 20 minutes, but be careful not allow the solution to dry on the siding. Scrub the siding with a soft long-handled scrub brush to remove the algae. Then rinse the siding thoroughly with cool water. The nice thing about oxygen bleach, is that it is not likely to damage plants, grass, or create instabilities in the soil.

If your algae/mildew is really bad, or if there are some very stubborn areas, then the next step up is to use a TSP-based cleaner. TSP is trisodium phosphate, and although this is an effective cleaner, several states have limited its use because of its negative affects on the environment. You will need to check with the manufacturer's recommendation to determine what the appropriate mixing level is for their particular product and the strength that you need. In addition to the environmental problems, the other downside of using TSP is that it can dis-color painted surfaces, wood and metal. So you will want to first test the TSP solution on a small area of your aluminum siding. And then before you apply the cleaner to the siding, you need to mask off any adjoining painted areas, to protect the paint. Once you've applied the cleaner to the siding, scrub the siding with a long-handled soft-bristle brush to remove the algae, and then rinse the siding thoroughly. You will need to wear protective googles, gloves, a hat and clothing if you are going to use a TSP cleaner.

Depending on the extent of your problem, you might want to consider using a pressure washer to clean off the algae/mildew off of your aluminum siding, and this can be combined with the use of a cleaning agent. However, if not used properly, it is very easy to damage your aluminum siding and create leaks.


Wear goggles, gloves, a hat and protective clothing when cleaning your aluminum siding, especially if using oxygen bleach and/or a pressure washer. And as mentioned above, you absolutely need to wear all of these protections and be extremely careful if you are working with TSP.

When you are spraying water on your siding, you will want to use a ladder, so that you are spraying downward, never upwards. Spraying upwards can lift and damage your siding, plus it can get water behind your siding, which can lead to rotting. Spraying downwards is of course very important if you are using a pressure washer.

You also need to be very careful if you are using a pressure washer, as it is very easy to dent your aluminum siding if you hit it with too much force.

If you are using a long-handled scrub brush, be sure to get on with soft enough bristles, so that you do not scratch your aluminum siding.

Aluminum does not flex like vinyl, so to prevent denting, you will need to be gentle with your scrubbing or spraying.

To limit the effect of chemicals on nearby plants, you should soak your plants and the surrounding ground BEFORE applying the detergent, oxygen bleach, TSP, etc. to your siding. And then thoroughly rinse your plants and surrounding ground afterwards.

And finally, routine maintenance is the best way to keep from having to use more aggressive methods of cleaning your aluminum siding. So if you know your home is in a location prone to the algae / mildew, then it is a good idea to plan to clean your siding once a year, before it gets a chance to build-up.

Hope this is helpful.
Home Wizard