Removing black algae stains from roof shingles

[Ray K]

When a roof has copper or galvanized items (vent pipes, exhaust fans, etc.) protruding from it, shingles below these items will be free of algae stains because rain washes copper or zinc from the galvanized items off and kills the algae. Has anyone heard of using a copper or zinc solution in a hose end sprayer to clean remove the stains? If so, which chemical, what concentration, and what coverage?

I'm experimenting with more conventional approaches (oxygen bleach, laundry detergent, and a produce called KrudKutter). All require multiple applications, "scrubbing" with a broom, and generous rinsing. There may be other proprietary (expensive) items that are more effective and easier to use, but for now I'm looking for shortcuts.

Thanks,

Ray

[spamTHISbrp]

Roof zinc strip? Just install, let the rain do the work. Don't know how fast the stains will fade, though.

Dave

[Ken]

You are correct about the zinc being responsible for SOME killing of the algae/fungus. I guess depending upon where you live, the results of such strips will vary? All I can say is that in the south where the humidity is high and the temperature is also, the strips do not work very well. There IS an improvement, but I do not see it as worth the effort.

Some years ago I attempted to remove the stains from my roof with a chemical made especially for this purpose. You can buy it at Home Depot I believe. It is mixed with bleach, sprayed on with a tank sprayer, and washed off with a hose or pressure washer at low pressure. The results were NOT total, but there WAS an improvement. The real problem was that the improvement was only temporary and if your neighbors had the same problem, it was sure to return next year, albeit not as bad.

If someone wants to make a fortune, they should find something that solves this problem and mix it into the asphalt used to make the shingle. As of this moment I do not think there is anything that really prevents the problem 100%. If there is, I would like to hear about it.

[Ray K]

The problem is caused by the limestone used in the construction of current shingles. It acts as food for algae. There are shingles made with embedded copper granules in them that prevent the algae problem. You just have know they exist and specify them.

The problem with adding zinc strips is that they will take too long to work. That's why I was wondering if there is a zinc (or copper) solution I could just spray on the roof to remove the stains fast.

[Paul Franklin]

All the zinc does is kill (or prevent from starting to grow) the algae and/or moss. It doesn't remove the stains. If you already have algae and stains, adding zinc strips will eventually slowly kill it, but it will take a long time for the stains to weather off.

Best bet is to clean the roof (bleach and TSP substitute worked for me, but did require scrubbing with a soft brush), and then add the zinc strips to stop or at least slow the return of the algae and/or moss.

Also, the zinc strips don't seem to work very well on shallow-pitch roofs, although you can add a second or third row of the strips lower down on the roof to help. But then they can be kind of ugly.

HTH,

Paul F.

[tnom]

A year ago I asked the same question that you are asking now. I had very noticeable black algae streaks on the north facing slopes of my white shingled roof. A reply directed me to

I tried this product and now I have no black streaks at all. This after just one application last fall. No scrubbing. Just spray and forget.

It does take time to work. The product stays in place up to a year and every time it rains it releases more algae killer. I believe the formula calls for a 9:1 ratio of water to chemical. Because of this I would suggest buying their low ratio sprayer also.

[Ray K]

Thanks, Paul. That's the kind of feedback I was looking for.

My house is a ranch, so your comment about shallow-pitch roofs applies to me.

Do you remember your concentrations of bleach and TSP? Why did you use TSP substitute?

Ray

[Ray K]

Thanks for the lead; it's one I hadn't come across before posting.

I may try it after I removed the bulk of the stains using other faster methods. Some of their prices seem extremely high, like $52 for a low-ratio hose end sprayer. Ortho makes one for about $10; unfortunately its lowest ratio is 8 oz/gal or 1:16. Ratio depends on hole size, a simple thing to change during initial design. That's why I can't understand Spray and Forget's high price. (No competition = high price.)

Ray