Over the last few years I have noticed some lichen growing on my house roof. It seemed to have started when some trees near the front and back of the house shaded the roof and kept the roof damp. Each year the lichen spread out more and covered the entire roof. Although the trees have now been removed, the lichen continues to grow.I tried scrapping them off, but they soon returned. There are fine rootlets that dig into the shingle tar and when scrapped away leave a small indentation. After searching the internet and reading Peter Horton in the Globe, there seems to be no cure for this problem.
However, I think I discovered a possible solution. Lichen is a composite plant growth of an algae and a fungus living together in a symbiotic relationship. See link ……. http://en.wikipedia.org/wiki/Lichen
Since you can kill algae in pool water with an algaecide, it might also work on lichen. Using this idea, I bought some pool algaecide called HTH Algae Guard (3x concentrated) and applied it to the greenish gray lichen. The next day the lichen turned brown and seemed to have died.
Over the next few days I applied some more HTH with a small brush and let it absorb for a few minutes. I tried to work only on a small area about two feet square so I could scrap off the lichen while they were still wet with the HTH.
I then used a hand scrub brush with strong bristles and scrubbed the lichen off while scrubbing the HTH into the shingle. Painting the roof with HTH will prevent further lichen growth. It was much easier scrubbing the lichen off after applying the HTH than without.
You can buy the HTH at any hardware or pool supply place. I bought mine at Walmarts. However, they only stock it during the summer season. You can see some photos of the lichen and the HTH materials in the link below …. http://picasaweb.google.com/markryan312/Lichen92510#
In the photos of the roof, you can see that the lichen has been removed from near the roof peek and along the right side. The area in the middle of the roof still has the lichen not yet removed but will be worked on later.
I would assume that the HTH might also be used to remove moss and mold growing on walkways, house siding and green stained yard furniture.
Comments and suggestions welcome: …. Send email to … markryan82@comcast.net
