roofs/to clean or not to clean


New Member
I've read that the mold on roofs eats at the granules on the shingles shortening their life span. Of course I've read this on pw companies web sites. 3M (shingle manufacturer) claims that the mold will not damage shingles and that it's strictly an aesthetic problem. It stands to reason that the fungi must feed on something so they will damage your shingles! So what's the truth?
Is there any scientific data out there I can arm myself with to support this claim? I've had a few potential customers hit me with this argument. I need some concrete evidence to overcome this kind of objection. A man convinced against his will is of the same opinion still.

thx as always,

Henry Bockman

New Member
I can't cite you any articles off hand but it's true, the mold, mildew and moss feed off of the roofing material and what ever is rotting on it's surface. Either way, it's mold and mildew on the house and quite a few people are sensitive to it. Another problem is when it gets heavy enough it can cause leaking problems when it grows up under the shingles. Water tends to get sucked into it and it will actually be siphoned up the roof line under the shingles where it will rust through nails or just leak around them.

If you have any questions about this or a client does, have them give me a call. I've been doing roofing repairs for 16 years now so I've seen what kind of damage it can cause..



The mildew will also draw in more heat causing the attic to get hotter which can ruin anything in the attic, cost more on utilities and cause wood to warp.


New Member
roof cleaning

So whats the best way to clean a roof? Can you use pressure? Do any of those miracle roof cleaning agents work?

steve r

PCP said:
So whats the best way to clean a roof? Can you use pressure? Do any of those miracle roof cleaning agents work?
Chlorine Bleach


New Member
Thank you Henry for your reply.16 years in the biz; I'm sure you've seen enough to know. It's good to know that what I'm pitching is comletely valid. Do you think roof sealants work or are they bs? What's the easiest way to qualify myself to spot leaks and repair shingles?

thanks again,

john orr

New Member
Technically, its algae, not mold, on the roof - assuming we are talking about the black streaks. This is the same stuff that lives on concrete. In my area, the streaking was being blamed (and some still think its true) on jet aircraft from local Navy airbases.

The algae has been around forever, but it was about 20 years ago that the shingle manufacturers started adding limestone as a cheaper filler in shingles. The result is a slight increase in the ph of the shingle. Older shingles did/do not have this problem.

While I can't speak from a scientific perspective, black absorbs heat and the algae hold moisture - two bad things for shingles. So I would say that having this algae on your roof can't be good.


New Member
Fungi and other wood eaters

Parasitic Mushrooms: Blights of the Forest?
Parasitic fungi have been the bane of foresters. They do immeasurable damage to the health of resident tree species, but in the process, create new habitats for many other organisms. Although the ecological damage caused by parasitic fungi is well understood, we are only just learning of their importance in the forest ecosystem. Comparatively few mushrooms are true parasites.
Parasites live off a host plant, endangering the host's health as it grows. Of all the parasitic mushrooms that are edible, the Honey Mushrooms, Armillaria mellea, are the best known. One of these Honey Mushrooms, known as Armillaria bulbosa, made national headlines when scientists reported finding a single colony covering 37 acres, weighing at least 220,000 Ibs. with an estimated age of 1500 years! With the exception of the trembling Aspen forests of Colorado, this fungus is the largest-known, living organism on the planet. And, it is a marauding parasite!
In the past, a parasitic fungus has been looked upon as being biologically evil.

That view is rapidly changing as science progresses. A new parasitic fungus attacking the Yew tree has been recently discovered by Montana State University researchers. This new species is called Taxomyces andreanae for one notable feature: it produces minute quantities of the potent anti-carcinogen taxol, a proven shrinker of breast cancer. (Stone, 1993). If this new fungus can be grown in sufficient quantities in liquid culture, the potential value of the genome of parasitic fungi takes on an entirely new dimension.
Many saprophytic fungi can be weakly parasitic in their behavior, especially if a host tree is dying from other causes. These can be called faculative parasites: saprophylic fungi activated by favorable conditions to behave parasitically. Some parasitic fungi continue to grow long after their host has died. Oyster mushrooms (Pleurotus osireatus) are classic saprophytes, although they are frequently found on dying cotlonwood, oak, poplar, birch, maple and alder trees. These appear to be operating parasitically when they are only exploiting a rapidly evolving ecological niche.
Many parasitic fungi are microfungi and are barely visible to the naked eye. In mass, they cause the formation of cankers and shool blights. Often their preeminence in a middle-aged forest is symptomatic of other imbalances within the ecosystem. Acid rain, ground water pollution, insect damage, and loss of protective habitat all are contributing factors unleashing parasitic fungi. After a tree dies, from parasitic fungi or other causes, saprophytic fungi come into play.
Saprophytic Mushrooms: The Decomposers.
Most of the gourmet mushrooms are saprophytic, wood-decomposing fungi. These saprophytic fungi are the premier recyclers on the planet. The filamentous mycelial network is designed to weave between and through the cell walls of plants. The enzymes and acids they secrete degrade large molecular complexes into simpler compounds. All ecosystems depend upon fungi's ability to decompose organic plant matter soon after it is rendered available. The end result of their activity is the return of carbon, hydrogen, nitrogen and minerals back into the ecosystem in forms usable to plants, insects and other organisms. As decomposers, they can be separated into three key groups. Some mushroom species cross over from one category to another depending upon prevailing conditions.
Primary Decomposers: These are the fungi first to capture a twig, a blade of grass, a chip of wood, a log or stump. Primary decomposers are typically fast-growing, sending out ropey strands of mycelium that quickly attach to and decompose plant tissue. Most of the decomposers degrade wood. Hence, the majority of these saprophytes are woodland species, such as Oyster mushrooms (Pleurotus species), Shiitake (Lentinula edodes) and King Stropharia (Stropharia rugoso-annulata). However, each species has developed specific sets of enzymes to break down lignin-cellulose, the structural components of most plant cells. Once the enzymes of one mushroom species have broken down the lignin-cellulose to its fullest potential, other saprophytes utilizing their own repertoire of enzymes can reduce this material even further.

Secondary Decomposers: These mushrooms rely on the previous activity of other fungi to partially break down a substrate to a state wherein they can thrive. Secondary decomposers typically grow from composted material. The actions of other fungi, actino-mycetes, bacteria and yeasts all operate within a compost. As plant residue is degraded by these microorganisms, the mass, structure and composition of the compost is reduced. Heat, carbon dioxide, ammonia and other gases are emitted as by-products of the composting process. Once these microorganisms (especially actinomycetes) have completed their life cycles, the compost is susceptible to invasion by a select secondary decomposer. A classic example of a secondary decomposer is the White Button Mushroom, Agaricus brunnescen.
Paul is the worlds leading authority on this stuff, bar none!

I hope this will lead you in the right direction in your research. It does not hurt to aquire a personal library so you can answer all related questions in a timely manner. I hate to not have the correct answer when I am doing a bid! :XXXXXXXX
As the cedar shingles lose their oils the "meat of the wood becomes weak and fodder for many microorganisms. It loses it's natural toughness as well as the repellants to ward them off. When you pressure wash it, the dead stuff blows off leaving the tough fibers that once held it all in place. I once found a group of small mushrooms growing in a shady spot on the rail of my deck. Fungus, mildew and mold will eat any wood if it has gone untreated long enough. Bet on it! :rolleyes:


New Member
The processes for cleaning asphault shingles and wooden shake shingle is greatly different.
The form of algae on your normal asphault shingle is called Gloeocapsa magma.This particular form of algae feeds on the limestone used in the shingles.


New Member
Wood is good

Yes, I realized that we were talking asphalt after the fact. I had no idea that those little critters could eat asphalt and limestone shingles! I just learned something new. Thanks! By the way, what does it look like when this is happening? Is it black, and on the exterior or under the shingles? :rolleyes:


New Member

yes it's black. usually you will see streaks under the vents where the roof remains clean. i think it's due to the copper or some other metal in the vents. i thought about charging people to install copper strips after cleaning but i'm not sure how effective they are or how long they last.

thanks for your lenghthy, informitive reply. i feel like i just graduated a biology class. unfortunately i will never be able to eat mushrooms again :)


New Member
Would you like mushrooms on that pizza?

They are now using fungi to eat mild toxic waste in boggy areas. You really do not want to eat those! Just don't pick the ones that glow! [puke]
Can you tell me how much pressure a power washer will drop as you add more hose? Being stricktly a wood guy, I will be doing shake roofs and I know I am going to need at least 200 feet of hose sometimes. Is it that great of a drop for every additional 50 feet of hose? I dont need a real powerful pressure washer but I wonder if a smaller one will be to week with too much hose. Thank you for your expertise.

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