Asbestos roof debris runoff after power washing (C) Daniel Friedman

Asbestos Cement Roof or Siding Power Washing Troubles & Warnings

  • ASBESTOS CEMENT SHINGLE POWER WASH - CONTENTS: Power washing an asbestos cement roof raises environmental contamination worries. Certification & Training for Asbestos Abatement, Cleanup, or Removal Workers & Companies. Warnings about un-trained asbestos cleanup workers. Lack of training or job supervision result in improper asbestos, lead, mold and similar contamination removal efforts
  • POST a QUESTION or READ FAQs about assessing the risk of damaged cement asbestos roofing and site contamination by asbestos fiber runoff after powe washing a roof

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Asbestos cement roof damaged by washing:

this article warns about un-supervised or un-trained environmental cleanup companies or work crews handling asbestos, lead, mold, and similar indoor contaminants, including identification of amateur or improper asbestos "abatement" projects that failed to properly remove materials or that left abandoned asbestos materials in place.

These warnings about using a power washer on an asbestos-cement roof also pertain to asbestos cement siding as well.

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Asbestos Cement Roof Washing Troubles - "... they power-washed my asbestos cement roof ..."

Asbestos roof debris runoff after power washing (C) Daniel Friedman Asbestos roof debris runoff after power washing (C) Daniel Friedman

Question: Is power-washed asbestos-cement roof runoff an environmental hazard?

I live in Brantford Ontario and a building in my neighbourhood has was I think is a corrugated asbestos roof. Last weekend some workmen power washed it. The run off, when dried, looked like grey powder and lifted from the pavement in "sheets" almost like parchment paper. I've attached a couple of photos. Does this present any danger or give cause for health concerns? - D.F., Brantford ONT

Reply: Asbestos hazards are probably present, asbestos regulation violations may have occurred, and further steps are needed


Corrugated cement asbestos roofingMost likely the debris that was washed off of the roof contains road and other environmental dust that had settled on the roof surface over time, and possibly algae, mold, or lichens that were staining the surface (as in our file photo of corrugated asbestos roofing - left) leading to the desire to wash the roof in the first place.

But because power washing is a strong approach to cleaning a surface it is likely to also have dislodged asbestos and cement particles from the asbestos-cement corrugated roof itself.

While wetting the material, something that would naturally occur during the power-washing of the cement-asbestos roof surface, would be expected to reduce the airborne level of asbestos during the actual washing process, although when properly peformed, wetting to control asbestos particle release includes the addition of a wetting agent to the spray before it is applied.

Power-washing a cement asbestos roof would leave substantial materials on the ground after the clening procedure. As the on-ground material dries asbestos fiber and particle risks are likely to be present.

So it would be no surprise if the debris on the ground around the building in your photos contains a high level of asbestos fibers and particles. The material therefore may form an airborne asbestos hazard in the neighborhood, or as it washes into local storm drains, it may constitute an illegal and improper disposal of asbestos dust and debris.

If the added cost to properly clean up this mess is going to be high (which we would guess is the case), it would be appropriate and inexpensive to collect a debris sample for testing by a local, certified asbestos testing lab to confirm that the contents are indeed contaminated at a level requiring professional cleaning.

In addition, power-washing the roof surface risks increasing the friable nature of the material that remains on the building, as the cementious binding has been removed from the uppermost roof surface, first by normal weathering and second, and much more aggressively, by the power washing process.

The building owners should address these questions immediately in order to reduce the spread and thus possible costs of a proper asbestos dust cleanup.

Asbestos regulations for Ontario are published under the Occupational Health and Safety Act and are in Ontario Regulation 278/05 and provide a clearly-written and comprehensive guide to cleaning up and disposing of asbestos containing materials in or on buildings. Discussing [Type 1] asbestos operations that regulation states:

1. Before beginning work, visible dust shall be removed with a damp cloth or a vacuum equipped with a HEPA filter from any surface in the work area, including the thing to be worked on, if the dust on that surface is likely to be disturbed.

2. The spread of dust from the work area shall be controlled by measures appropriate to the work to be done including the use of drop sheets of polyethylene or other suitable material that is impervious to asbestos.

3. In the case of an operation mentioned in paragraph 4 of subsection 12 (2), the material shall be wetted before and kept wet during the work to control the spread of dust or fibres, unless wetting would create a hazard or cause damage.

4. A wetting agent shall be added to water that is to be used to control the spread of dust and fibres.

5. Frequently and at regular intervals during the doing of the work and immediately on completion of the work,

i. dust and waste shall be cleaned up and removed using a vacuum equipped with a HEPA filter, or by damp mopping or wet sweeping, and placed in a container as described in paragraph 5 of section 15, and

ii. drop sheets shall be wetted and placed in a container as described in paragraph 5 of section 15, as soon as practicable after subparagraph i has been complied with.

6. Drop sheets shall not be reused.

7. After the work is completed, polyethylene sheeting and similar materials used for barriers and enclosures shall not be reused, but shall be wetted and placed in a container as described in paragraph 5 of section 15 as soon as practicable after paragraph 5 of this section has been complied with.

Watch out: in 2010 The New York Times reported that

65 to 80 percent of those receiving certification as qualified asbestos removal experts had not received the necessary training.


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