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Presidential Pressure Washing wrote:

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I found these 2 articles and they have some very, very good info, I would like to see the opinions if you would on what conclusions you are drawing from them..
Let's see if we are on the same page or maybe I am crazy... idk

This was published in 2000
http://docserver.nrca.net/pdfs/technical/5821.pdf 

btw there is more than one strain on the roofs, anyone heard of Scytonma?? this is the second leading cause of roof discoloration.


Now here is a publishing in 2009

http://docserver.nrca.net:8080/technical/9341.pdf

Kim R

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It is a roof cancer that responds best to Apple Cider Chemotherapy

Ok So no one is going to take a guess or maybe you all have been really busy,
I will sum up my take on the 2 articles.

In 2000 3M worked on developing a additive to the shingle to curtail the growth of algae, Bad for us... right... ok...

Well the second study 2009 from my gathering is that while it may initially block the growth of algae, the testing models are showing a discrepancy in effectiveness of the additive, there is a few factors that raised issues, how much to add in to be effective, and if too much is needed then it would not be cost efficient.
As well as distribution to areas based on severity of algae strains.
Bottom line it is unpredictable and attempting to maintain cost effectiveness is the struggle.
So right now the major shingle manufacturers are still waiting for real time results as opposed to the artificial lab studies.

In summing this up my impression is they thought they had it worked out with the copper additive, but 9 years later considered inconclusive and needs more real time studies.
So these two articles I think are reassurance of job security and the bonus thrown in is the zinc additives theory as it is shown to not be effective due to the cause of  discoloration from leaching a white powdery substance on the roof surface. So that Z's that out.
Plus there are some other good things hidden in the research.
Please correct me if I digested this info wrong, it has been a long day.
Kim R