Black shingle stains (C) Daniel FriedmanExtractive Bleeding - Black Stains on Asphalt Roof Shingles
Does extractive bleeding really occur on roof shingles? Causes & Diagnosis of extractive bleeding stains.

  • EXTRACTIVE BLEEDING on SHINGLES - CONTENTS: Black or dark extractive bleeding stains on roof shingles - how do we sort out roof stains caused by algae, extractive bleeding, soot, debris or other causes?Diagnostic Guide to Extractive Bleeding Stains on Roof Surfaces. Definition of extractive bleeding roof shingles - does it really occur? Causes, cure, and prevention of extractive bleeding black stains on roof shingles
  • POST a QUESTION or READ FAQs about how to diagnose, clean off, or prevent stains on roof surfaces, including extractive bleeding, algae, dirt and debris, moss, lichens

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Extractive bleeding stains found on asphalt shingle roof surfaces:

Definition of extractive bleeding; does extractive bleeding actually occur? what is extractive bleeding on roofs? Extractive bleeding can occur in some roofing products and is an asphalt shingle or roll roofing defect often confused with algae or other roof stains as well as an actual product failure. Is extractive bleeding different from black stains caused by roof algae?

Joining other roof stain sources, extractive bleeding stains on roof are part of a catalog of the types of black stains that are found on roofs. Black or dark stains on building roofs may be traced to extractive bleeding (or more often algae staining) where we find some asphalt shingle roofs offering a prime example.

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BLEED THROUGH - Black Bleed-Through or Extractive Bleeding Black Stains May Occur on Asphalt Shingles or Roll Roofing

Extractive bleeding - bleed-through asphalt shingle stains may be mistaken for but are not black algae or black "fungus", nor are they soot. Extractive bleeding stains on asphalt shingles are caused by loss of black pigment in the asphalt mix intended to impregnate the shingle mat itself.

Photograph of possible asphalt shingle bleed-through or extractive bleeding on asphalt roof shingles (C) Daniel Friedman Photograph of possible asphalt shingle bleed-through or extractive bleeding on asphalt roof shingles (C) Daniel Friedman

Extractive bleeding or "bleed through" stains leaving black streaks running down an asphalt shingle roof is an indication of a defective roofing product. The chemistry of the shingle is permitting black pigment from the asphalt to leach to the shingle surface and run down the roof. Typically bleed-through on asphalt shingles appears as black streaks running down shingles.

You'll see black streaks of varying length and width (photos above and at page top).

Other black stains on roofs correlate with the growth of algae, the presence of roof debris or with soot from chimneys, particularly where an oil fired heating appliance is not operating properly. See Catalog of Black Roof Stains.

Let's look further at extractive bleeding type stains:

See Causes of Roof Stains and  Catalog of All Roof Stains for the causes and types of stains that occur on building roofs. There are other sources of roof staining, from cosmetic to harmful to the roof. For the diagnosis and cure of other building stains,

Extractive bleeding on roof shingles originates at individual points: When the roof shingle staining or bleeding appears to run down the roof, originating from individual small points or "spots" (photos above) this is probably extractive bleeding or "asphalt roof shingle bleed through" on shingles - a product defect described by manufacturers as cosmetic.

Extractive bleeding occurs on asphalt shingles when an excessive amount of bitumen is released from the shingle surface - we pose that this effect may occur because some of the bitumen was not well bound in the asphalt mix.

Furthermore, bleed-through stains, since they are a feature of the asphalt shingle product itself, should occur on a roof regardless of the roof orientation, slope, or shading.

By comparison, the location and pattern of black algae stains on an asphalt shingle roof are more likely to correlate with shade, areas of less sun exposure, or slope orientation (North) - factors that affect roof surface moisture, temperatures, and sun exposure - factors in algal growth. We describe and contrast BLACK ALGAE STAINING in the next section, just below.

Because of variations during the shingle manufacturing process, and possibly because of variations in site conditions (sun, shading, slope, moisture), different roof areas or slopes on the same building may display different amounts of black staining. This term is commonly used with wood shingles where use of steel or possibly even copper nails can also produce staining. (Try stainless steel nails when re-roofing with wood shingles or shakes).

Also see ROOFING MATERIAL DEFECT / environmentally-caused roof shingle stains for more examples of this problem.

Remedies for bleed through staining on asphalt shingles: we wouldn't do much to a roof with this staining since we worry that power washing or chemical treatments may reduce the remaining roof life. At re-roof time you might want to purchase a better-grade replacement shingle.

Background on Asphalt Roofing Shingle or Roll Roofing Black Bleeding Stains

Extractive bleeding is a term often applied to problems with paint or coatings over resin-containing wood products such as western red cedar shingles. But it has also been used in the roofing industry to describe bleed-out stains from asphalt roofing products. "Bleeding" in this context refers to the penetration of color from the underlying surface.

Are all black roof stains algae? Some roofing experts such as Norman opine that the bleeding stains we discuss here are due to algae. Certainly in many cases black stains on asphalt roof products are due to algal growth, not extractive bleeding.

See BLACK or GREEN ALGAE for a description of black stains on roofs due to algae. Readers will notice that the pattern of stains we ascribe to algal growth (and include in roof photographs) do not appear as originating at a point. Where we find algae stains on roofs it appears in wider areas, it does not originate in an inverted vee point, and it is correlated with other roof conditions such as shaded spots or spots that tend to stay wet. There is less algae growth in areas of more sun.

Also, on roofs where there is wash-down of salts from copper or aluminum flashing, you will see that it's effective in killing off algae (as well as moss and lichens).

But on a roof with extractive bleeding you will see that the mineral salts washing down from similar flashings and metal at higher points does not make much of an impact on the black stain.

Extractive bleeding of asphalt roof products was described in a peer reviewed professional journal, in an interesting article
A Performance Approach to Aging Tests for Bituminous Roofing Membranes, under a discussion of roof weathering tests where the researchers defined changes in the surface appearance of roofing materials and named categories A-F:

A: no significant change
B: Paler, otherwise no significant change
C: Darker
D: Darker and brownish
E: Black staining, "bleeding", and embedment of surface mineral matter
F: Dull black and formation of elephant skin.

Bleeding of bituminous material was readily identified as a surface stain or discoloration on the roofing membrane.

We pose that the loss of bitumen might signal a reduced roof shingle life for two reasons,

  1. Shingle bleeding stains may be a clue that the asphalt mix for the particular shingle batch lacked adequate bonding, and
  2. The loss of substrate material from a shingle may correlate with aging and wear.

    A change in shingle weight is the dominant feature appearing in shingle wear and the same article explains that loss of weight (caused by loss of surface material or loss of membrane material) correlates with shingle wear and life. Loss of volatile material correlates with loss of shingle flexibility which is a contributor to shingle wear and ultimately tears or cracking.

Some roofing consultants, including Mr. Norman (above) assert that many of the black stains on asphalt shingle roofs are due to algae growth and that extractive bleeding may not be a current roof problem.

Free Testing Offered to Identify Roof Stain Material: see ALGAE STAIN TEST METHODS for a description of both free lab tests and do-it-yourself roof stain tests that can help decide on the cause, clean-up, and prevention of algae stains on roofs.

See BLACK or GREEN ALGAE STAINS on ROOFS for a description of black stains on roofs due to algae

To remove and prevent black algae stains on roofs,

This article series tells readers how to identify & explain the most-common causes of black, brown, red, gray, green, or white stains appearing on roof shingles and on other building surfaces. Roof shingle stains are often caused by black algae, bleed-through or extractive bleeding of asphalt, dirt, soot, or organic debris.


Continue reading at ALGAE STAINS on ROOFS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see EXTRACTIVE BLEEDING SIDING STAINS - extractive bleeding stain problems on wood siding

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

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EXTRACTIVE BLEEDING on SHINGLES at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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