Tips to Clean Algae Discoloration!

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  • Author C. Michael Hunter
  • Published December 9, 2011
  • Word count 556

Algae discoloration is a prevalent problem on asphalt roofs, especially those in warm and humid places. While it does not really cause serious harm, it can significantly alter the look of a house, making it appear old and dirty due to the differences of the color on the shingles. The natural look of the roof can be restored with the following simple cleaning tips suggested by a professional roofer.

Cleaning Tips

Removing algae from the roof is fairly easy. Like most plant life, it cannot survive a dose of chlorine bleach and trisodium phosphate. To get the right mixture, a cup of chlorine should be mixed with a cup of trisodium phosphate and then be diluted with a gallon of water. It is best applied by using a two-gallon sprayer and spraying it directly over the algae-infested area.

After spraying it on the top of the house, rinse the solution off with clean water using a hose to avoid any further staining from the bleach. When rinsing, do not spray directly against the shingles as this may cause the water to penetrate the roof. Instead, spray along the direction of the shingles to mimic the natural fall of rainwater. Since not all the algae will die with just a single application, the spraying and rinsing should be done in three consecutive sessions to ensure optimum results and overall coverage.

Before every session, cover the vegetation surrounding the house with plastic sheets to protect it as the solution is deadly to a variety of plants.

Permanent Solution

Homes located near bodies of water such as lakes and homes in warm and humid places will likely be plagued with algae just a few weeks after cleaning. In these cases, there is an effective method that is used by roofing contractors to get rid of an infestation of plant life permanently through the use of zinc strips. Just like the cleaning solution, zinc molecules are deadly to plants including algae.

The zinc strips can be installed at several points along the ridge. During a rainfall, the run-off will automatically wash off the zinc molecules into the algae spores that may have landed on the roof. It will instantly kill the spores and prevent them from thriving.

Safety Reminders

Keep in mind that working on roofs, especially ones with algae, is very dangerous. There is always a risk of slipping and falling when climbing on these structures. Be sure to wear rubber-soled shoes to reduce the risk of slipping.

Goggles and a mask should also be worn when spraying. Tiny droplets of the solution are easily carried by the wind so there is a high risk of inhaling it or getting in the eyes, which could cause eye or bronchial irritation. Goggles and mask should protect a worker when spraying.

Assign a spotter that will serve as a lookout while working. There is no telling when a fall could happen. A lookout will serve as a first responder in case of a fall and can call for emergency aid as well as provide support when climbing the ladder.

An algae infestation on the roof can be a real eyesore, yet it is something that is easily manageable. Hopefully this article has provided helpful tips on how to clean up algae discoloration and how it can be done safely and effectively!

C. Michael Hunter is an expert in residential and commercial roofing. To find out more about Houston Roofs, go to the main website at:

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