Shingle lichen removal ?

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Old 08-28-15, 06:23 PM
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Shingle lichen removal ?

We have an extensive size asphalt shingle roof where I work that we want to rid of some what looks to me like maybe lichen growth from the shingle edges. In addition there is some (but not a lot yet anyway) actual certain moss growth too (green like the moss I'm familiar with) which of course I'd like to stop/prohibit too, but these white or light colored spots/buildup on the shingles as can be seen in the photos below is what I'd like to get rid of before it gets much worse. Don't have the budget to go out and buy a big bunch of expensive chemical special treatment product. We do however have a lot (plenty) of bleach which I was thinking of mixing maybe 50/50 with water and spraying on these spots with a manual spray tank/wand, if that is supposed to work good. Otherwise I also have a pressure washer which I could set to a decent reasonable low pressure and probably blast the stuff off without damaging the asphalt shingles. Although usually they say using a pressure washer on asphalt shingles is a big no-no. I could see that with using excessive pressure but going along with just enough pressure to do the job seems to me like it would probably be okay. Any comments/suggestions appreciated.





 
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Old 08-28-15, 06:32 PM
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I've found out that lichen is caused by airborne allergens that land and germinate on the roof.
Pretty interesting..... huh.

You can wash the roof with a solution of one cup TSP (trisodium phosphate) and one gallon of bleach mixed with five gallons of water. If you use a five gallon bucket.....that will be a gallon of bleach to four gallons of water. A little stronger and more effective.

Just spray it on..... let it sit for a while and then hose it off. Don't brush it on and don't use a pressure washer or you'll remove those roofing granules.

The good news is it will be clean after that. The bad news is that it will probably reoccur.
 
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Old 08-28-15, 06:49 PM
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Ok PJ but how necessary it the TSP really? And how about if I spray on the bleach/water but don't bother rinsing it off? And for sure the pressure washer would most certainly remove the shingle granules, even if not that high of pressure?
 
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Old 08-28-15, 06:55 PM
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You could certainly just try the bleach.

I don't recommend a pressure washer to be used on roof shingles. You can certainly try it if you want.
 
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Old 08-28-15, 07:33 PM
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Adding zinc strips to your roof will keep the lichen from coming back

This video might be helpful: Preventing Roof Moss with Zinc Strips | Video | This Old House
 
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Old 08-28-15, 08:37 PM
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You could certainly just try the bleach.
I don't recommend a pressure washer to be used on roof shingles. You can certainly try it if you want.
Ok I might go ahead and try just the bleach. Maybe a 1:4 part ratio of bleach to water. With no TSP and with no rinsing afterward. I'll check in a week or two to see if there is any obvious improvement happening after trying that. If not, maybe I'll go ahead carefully with the pressure washer then.
 
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Old 08-28-15, 08:45 PM
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Adding zinc strips to your roof will keep the lichen from coming back
This video might be helpful: Preventing Roof Moss with Zinc Strips | Video | This Old House
Yeah if I can get rid of the lichen/moss that's already present I'll be strongly considering/suggesting the installation of zinc strips to prevent the stuff from coming back. Hopefully it'll be something we can work it into the budget. It's not particularly all that expensive I don't think to buy the zinc strips, but of course not cheap either. If zinc strip really do work to prevent re-occurance of the moss/lichens in the long term though then it would be well worth it. thanks
 
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Old 08-28-15, 08:50 PM
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Yeah I'm not so sure the lichen will come off easily if it is the same type that grows on the trees bark and stuff around here. It's similar to a barnacle in some ways! Course maybe that was YEARS worth of lichen... the old dead lichen was almost like bark itself... stuck to old cars parked in the grove and everything!
 
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Old 08-28-15, 09:17 PM
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Not sure if my roof lichen is the same type that grows on trees bark but it does seem to resemble that photo linked. I wouldn't say it seems like any barnacle I've ever seen, certainly not hard like a barnacle but actually kind of soft/fluffy like when you scrape it off. When you do scrape it off it a little residue still remains I noticed. Just this year it seems to have occured for some reason; never saw it occur in past years on this roof. Maybe it was there but not really noticeable until this year. I dunno.
 
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Old 08-29-15, 09:52 AM
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Actually upon reading "researching" the internet about roof cleaning, ridding of moss/algea/fungus etc from asphalt shingled roofs I find dozens of methods, procedures, mixtures/ratios of this or that, many contradictory as to what is supposed to work and what doesn't. A guessing game really as to what to do, what not to do, what'll work.
 
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Old 09-03-15, 01:36 PM
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update: a week later

So I decided after a little more research to try spraying a mixture of 50/50 bleach/water (1/2 gallon of each), mixed with a 1/4 cup dish detergent onto the roof lichen stuff. Here a week later after that application it looks slightly, if at all, different than before, and I think the lichen feels more flaky/crumbly than before when it seemed more spongy. Hard to tell if the lichen stuff is dying or dead or just the same before as before really.

I'll be sure to keep ya'll updated with another "progress report" a week from now. Betcha can't wait, eh?

 
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Old 09-06-15, 07:16 PM
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I live in the Southeast and have a similar problem with dark algae streaks on my roof. This site recommends a DIY of 50% bleach and 50% water for 20 minutes then a rinse. Unfortunately, there is a risk of drying out asphalt shingles using bleach. I wish this issue were addressed on the forums. what good is a clean roof if you reduce it's useful life in the process?

Any recommendations to share?

Thank you ...
 
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Old 09-06-15, 07:29 PM
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Diydud, dark algae streaks also is common on asphalt shingle roofs here in, Southeast Alaska. I've tried the bleach/water method you mention, with just slight and barely noticeable improvement, not worth the effort and wouldn't recommend it or bother trying it again.
 
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Old 09-06-15, 07:58 PM
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This then begs the question: what is the solution? How are we to clean our roofs? I ask because a co-worker paid $700 for a roof and fence cleaning and he was very pleased with it.

If I could only figure out what they used ...
 
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Old 09-07-15, 04:42 AM
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IMO a bleach/water solution works best but I question the 20 minute wait time as you are working against yourself if you allow the cleaning solution to dry before rinsing. Sometimes adding a detergent to the mix can be beneficial.

Often a pressure washer is used to aid in the cleaning and while that method is great for siding/fence it should not be used on a shingle roof! It is very effective at cleaning the roof but will shorten the life of the shingles. I used to live in fla and came to the conclusion the best method for combating mildew stains on roofs is to use a darker colored roof that won't show the stains as readily.
 
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Old 09-07-15, 06:03 AM
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This is the most authoritative instruction that I have been able to find to-date and pretty much follows what has been stated within this thread:

http://www.asphaltroofing.org/sites/...icle%20May.pdf
 
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Old 09-07-15, 09:34 AM
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How long then should the solution stay on the roof before rinsing? Just a few minutes maybe depending on temperature and humidity -- just long enough before it might start to dry? What determines whether adding detergent to the mix might be beneficial or not?

Edit: I just saw Info in link posted by diydud's previous post says let the roof solution dwell for 15-20 minutes and maybe longer is necessary but avoid letting it dry as that may prevent complete rinsing. Nothing mentioned about the addition of detergent. Although apparently it is important to rinse off the solution, it also says "algae will disappear and wash off with subsequent rains", so I'm not clear about why it's so necessary to rinse. In my geographical location it rains so often I can count on it raining soon/often so I that's why I when I previously tried the bleach/water method I didn't worry much about doing the rinsing; maybe that's why it didn't work so well I suppose...
 

Last edited by sgull; 09-07-15 at 09:52 AM.
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Old 09-07-15, 11:12 AM
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Sgull,

I am planning a limited test of this solution on a part of my roof in the next few days. My plan is to spray it on an area of less than 10 square feet, let it sit, then rinse. I am hoping to do this immediately before one of our daily downpours ... to further rinse the shingles AND to prevent foliage from being fried by the mixture. It probably would have been better to do it last month as we got 14 inches of rain during August!

I'll let you know how it goes. If I have the time I will attempt before and after shots.
 
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Old 09-07-15, 11:35 AM
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Diydud, will you be adding any detergent to the mixture? Looking forward to hearing about or seeing results of your limited test.

Another thing, the chlorine bleach I used was really old. In storage in its factory gallon containers for like 6 years. I smelled it and didn't even have a smell. After thinking/wondering about that, I just did some internet "research" and apparently bleach does in fact go "bad" over time. So I might invest in some new bleach and try a limited experiment myself with that.
 
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Old 09-07-15, 11:40 AM
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When the cleaning solution dries out on the substrate it allows the crud it started to dissolve to harden back up making it harder to rinse off. As mentioned in that link you are supposed to not let the cleaning mixture dry before rinsing. I'm not sure how you could wait 20 minutes without it drying unless it was a damp cloudy day [which is ideal cleaning conditions]

Detergent can serve a two fold purpose; extra cleaning ability and it can slow down both the run off and evaporation.
 
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Old 09-07-15, 11:57 AM
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So what kind of detergent might be best, and how much in the bleach/water mix? TSP seems to be a commonly suggested detergent additive, but will any kind of detergent do as well, or is TSP better suited for the task for some reason?

Here's a link of a video/info which shows it probably being done right, although I don't think it happens to mention adding any detergent or the rinsing off step: How to Remove Roof Moss | Video | This Old House Plus, I noticed the white stuff they're trying to get rid off looks like what I have and was calling lichen, but the linked video/info refers to ridding of moss. So maybe mine is moss, not lichen like I was just assuming.
 
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Old 09-07-15, 12:34 PM
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TSP is a heavy duty detergent, I don't know if it's any better than other heavy duty detergents. I've always tended to mix my bleach/water solution strong - about 50/50. It's hard to say when you need to add detergent, I often do it after I realize that bleach water alone won't do the job. While I've washed shingle roofs before I've not done a lot of them as that it probably one of the more difficult substrates to clean and get a nice looking job without damaging the shingles.

There are 2 ways to keep the cleaning solution wet; reapply as needed or mist the roof with water. A combination of those two is probably best.
 
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Old 09-07-15, 12:49 PM
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So I wonder how much TSP to use per gallon of 50/50 bleach/water? I have a lot of roof to do and don't want to over-do the amount of TSP I add, to keep the cost down. Will cost enough already, just buying the bleach.

I wonder about the idea of applying the solution to the roof on a "drizzly day" where the roof stays wet but not really rapidly running off wet.
 
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Old 09-07-15, 03:46 PM
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It's been awhile since I've used TSP but if I remember correctly I normally mix about a 1/2 cup [not that I measure] in with about 2 gallons of bleach water. It should say on the label what the ideal mixture is.
 
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Old 09-07-15, 04:06 PM
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Ok will get some new bleach, some TSP, and give it go, again. See what happens. Thanks.
 
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Old 09-08-15, 05:18 AM
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Another VERY interesting link on the subject of controlling algae growth on asphalt roofs ... with actual test results:


How to Remove and Prevent Black Algae Stains on Asphalt Shingle Roofs | Today's Homeowner
 
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Old 09-08-15, 08:15 AM
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From the "it worked for me..." file...
Several years ago I had a cabin surrounded by nice shady oaks which allowed green moss to grow on the roof. I went to a local grain elevator to see if they had any miracle treatment and instead was sold a bag of cheap ordinary fertilizer. He explained that the idea is to broadcast the pellets on the roof and the nitrogen will burn/kill the moss. It worked and eventually the dead bits fell off.
I never got around to attaching strips of zinc to the peak as future prevention but I can tell by my neighbors houses that those strips DO work and last many years.
 
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