Extractive bleeding roof stains (C) Daniel Friedman Roof Algae Stain Identification & Cure

  • ALGAE STAIN TEST METHODS - CONTENTS: How to test for black algae growth and stains on roof surfaces. Algae stains and black marks on asphalt roof shingles: causes, effects on roof life, cure & prevention. Types & photographs of organic felt asphalt roof shingle defects & failures
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Identification, cure & prevention of algae stains on roof surfaces:

Tests, removal or prevention of black algae & other stains on roof surfaces. This article explains methods used to test for and confirm black roof stains due to algae or "black fungal growth" on roof shingles. We provide a list of type of stains and colors that appear on roof shingles and on other roofing materials.

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Testing to Identify Roof Stain Material

Algae stains on a roof (C) Daniel FriedmanSome roofing consultants, including Mr. Norman (above) assert that all of the black stains on asphalt shingle roofs are due to algae growth.

But we found some experts describing an occasional product defect that produces extractive bleeding in asphalt roofing materials. Extractive bleeding occurs in other building materials as well.
See EXTRACTIVE BLEEDING on SHINGLES for more on extractive bleeding;

To test black roof debris for a determination of whether the black stains are due to soot, algae, fungus, or asphalt bleed-through our forensic lab will accept tape samples for processing at no fee between April 2009 and June 2009.

Select a roof material testing laboratory or any forensic or biological test lab that can identify mold, algae, and particles.

Use the tape sampling procedure and mailing instructions found at TEST KITS for DUST, MOLD, PARTICLE TESTS to send off lab samples for testing. (No more than two samples per roof should be necessary. If pre-arranged by email, offers limited pro-bono roof stain sample analysis in our own forensic laboratory.)

Be sure to press your tape firmly into the black stain material.

Testing Black Roof Stain Material in the Forensic Lab

In our forensic laboratory (not on a roof itself) we prepare a microscope slide of black roof debris particles for direct examination at low and high magnification. Algae is identifiable by physical characteristics.

If the black material does not appear to be an organic structure we use a solvent on the microscope slide. Xylene or Hexane will cause asphalt products to bleed and stream on a microscope slide.

Algae stains on a roof (C) Daniel Friedman Algae stains on a roof (C) Daniel Friedman

Our photos above show black stains on a roof and an initial lab photo of the black roof debris at 400x.

Sample material from the stained area on this roof was prepared on a microscope slice and mounted in lactic acid. Lactic acid does not dissolve asphalt but that will hydrate and expand algae and mold spores. The debris in our photo (above left) looks like brownish black something that is not organic.

But take a look at the photographs just below.

Algae stains on a roof (C) Daniel Friedman Algae stains on a roof (C) Daniel Friedman

Here is what that same sample looks like under the microscope at 1000x, oil immersion, after allowing five minutes for hydration (expansion of the cells of material.)

We see a dark algae on the left and green algae on the right, both found in the same sample material. The black stains on the roof above are definitely algae, not bituminous material.

Testing Black Roof Stains On the Roof

Mr. Norman proposes a simple test of applying a light spray of a diluted mixture of trisodium phosphate [use a TSP substitute, not TSP which is an environmental contaminant] and chlorine (with water) in the proper proportion will determine weather or not this is algae quite readily. If it is asphalt pigment, it will not lighten.

If the residue is bitumen, a petroleum product would be necessary to remove it, but cleaning the roof with any solvent would of course be unwise as you will also damage the shingles as well as risk a fire, explosion, and environmental contamination.

This website tells readers how to identify & explain the most-common asphalt roof shingle failures and how to obtain asphalt roofing shingle failure claims assistance. These defects occur on organic-mat or fiberglass-mat asphalt roof shingles. Readers are also invited contribute roof failure information to the web author for research purposes. web author for research purposes.


Continue reading at BLACK ROOF STAIN CAUSES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see STAIN DIAGNOSIS on ROOFS for a complete catalog of roof stain sources & causes


Or see these

Roof Algae Lichens Moss or Stain Articles


Suggested citation for this web page

ALGAE STAIN TEST METHODS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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