Roofing Tips: Removing Algae Stains Part I

Pressure Wash IconDo you have unsightly algae stains on your roof? Tempted to go up there yourself with a pressure washer? Wait! Jared has some great tips for cleaning your roof – without creating more problems.
Jared: Let’s go to Barry in Orlando. Barry, you are In the House. How can we help you?
Barry: Hi. I’ve got some mildew on my roof, and I’m looking for either a commercial solution or maybe some concoction I can make up that’ll clean the mildew off but not damage my asphalt roof.
Jared: Good question, Barry. Are you planning on doing that yourself, or are you going to hire somebody?
Barry: No. I’d like to do it myself. The people that want to do it are a little pricey.
Jared: Okay. The Asphalt Roofing Manufacturer Association (ARMA) has specific guidelines on what you should do when cleaning the roof. That is who I would suggest you reference just to make sure that you’re doing the right thing.
Basically, what they’re going to say is, one, you don’t want to use pressure; a pressure washer will damage your shingles. And next, they suggest you take 1 gallon pool-grade chlorine. To it add 1 cup of TSP, or trisodium phosphate. You can also dilute it; 1 part water and 1 part pool-grade chlorine. I usually would just do it straight; you don’t need to spray as much on that way, obviously, when you don’t dilute it.
Then, you put that in a pump-up sprayer; make sure that you have one that has no metal parts on the interior components, only plastic parts. You don’t want to use a pump-up sprayer that you plan on using for other things, because once you have this pool-grade chlorine in it, it’s not going to do well for other stuff. Next you just mist or spray that on the roof, let it sit a few minutes, and then you can just rinse it right off.
Understand that any chemical that is strong enough to kill the plants that are growing on top of the roof – meaning the mildew or the fungus or the algae – is also strong enough to kill your plants around the outside of the house. Do you have gutters on your home?
Barry: No.
Jared: Okay. It is definitely more challenging without gutters because what’s going to happen is all of that pool-grade chlorine is going to come down from the roof, and most of us have plants right along the bottom of the section of our home. What most of the cleaning companies will do is they will have one person up on the roof and then one person on the ground. The person on the ground is constantly spraying their plants with water to keep them wet so that the chlorine doesn’t sit on them. That is one method.
Or you can actually cover the plants with some sort of plastic or tarp. I don’t want you to do that during the summer, because it’s going to trap the heat in so much that it will kill the plants. In cooler weather, you’re fine with covering them with some sort of plastic.
When you rinse your plants, you can use a pressure washer as forced water, but you want to stay back a few feet. You don’t want to put the pressure on it so you’re actually using the pressure to remove the gunk. You want to just use it as forced water.
Barry: Okay. Do I spray it on a dry roof, or should I wet the roof first?
Jared: Dry is fine, because then it’s not diluted, and it’s going to get right in there and actually clean it.
Barry: The other substance you said was TSP?
Jared: Yeah, TSP, which is trisodium phosphate; any big box store is going to have that, and it does a great job. You just mix it up. Just watch about breathing this stuff or getting it on your skin. It is a harsh chemical.
Any time you take on a project yourself, use caution and be careful to follow all safety precautions. Always check with the product manufactures for their recommendations too; some DIY processes may invalidate manufacturer warranties. You may want to reconsider and just pay a licensed professional to do the job; we recommend a local company called Mallard Systems who do great work. Thanks for the question, Barry, and good luck.
Read Part II of Roofing Tips: Removing Algae Stains.
For more information on roof cleaning, visit the ARMA website or watch the ARMA Guide to Algae Discoloration videoListen Saturday mornings to “In the House”. Get more Home Tips and show info at the In the House website. For a free inspection and estimate on your next Home Improvement Project, visit Universal Roof & Contracting or call now. Orlando: 407-295-7403 Jacksonville: 904-647-3907.