Asbestos Roof Cleaning

Steam Cleaning | Closed Box Method | HSE Guidelines

IMPORTANT: Before undertaking any works on an asbestos roof, safe access must be in place.
Please see our asbestos roof access page for more details.

With age, the surface of an asbestos roof is likely to be discoloured and, unless it’s been regularly maintained, it is also likely to be covered in moss, algae and lichen, all of which in the long term, can create significant problems.

Before asbestos roof cleaning
Typical asbestos cement roof with moss and lichen growth

This page discusses the merits of asbestos roof cleaning and the reasons why this maintenance should be done, along with situations where cleaning should not be attempted.

Although some people are of the opinion that this aged look adds character, lichen in particular can cause severe damage if it grows through to the underside of the roof, when asbestos contamination inside the building can occur.

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We recommend that roofs affected by moss and lichen are cleaned off and then sealed / coated.

Once cleaned, an asbestos roof should not be left untreated because the newly cleaned roof surface will encourage faster and more aggressive moss growth.

As you can see from the two images above, the moss actually eats in to the roof fabric, which delaminates and breaks off.

There are several methods of cleaning an asbestos roof and it should be noted that in certain cases, the cost of health and safety equipment (scaffolding, netting etc) can exceed the actual cost the materials used in coating afterwards!

Scraping

A heavily mossed roof should be dampened and the moss and other vegetation scraped off or loosened prior to the roof being properly cleaned.

This can be done using soft brushes or plastic scrapers, but it is very important that the surface is thoroughly wetted beforehand.

When carrying out an asbestos roof cleaning exercise, moss and other debris on the roof should be collected and placed into approved asbestos waste bags for proper disposal, since it could contain asbestos fibres, in which case must be treated as contaminated waste and disposed of properly.

NEVER USE JET WASH LANCES ON ASBESTOS ROOFS!

asbestos roof cleaning warningJet washing with lances used to be a common method for cleaning asbestos roofs but it has several problems including:

  • breaking down the cement matrix, causing fibre release
  • asbestos fibres cannot absorb water
  • creates large amounts of  slurry containing asbestos fibres 
  • pressure jets disburse any asbestos fibres and debris that might be present

We have seen many examples of inexperienced operatives cleaning asbestos roofs with high pressure jet wash lances.

This should be avoided at all costs and if a contractor suggests the use of this method for cleaning, you need to choose another contractor!

In 2012, a roof coating contractor was employed to clean an asbestos roof at Wrexham College prior to sealing. Unfortunately, they used pressure washer and lances and severely damaged the roof. The subsequent clean-up and decontamination is said to have cost in the region of £200,000. The story was reported here. The coatings company concerned later went into voluntary liquidation.

Remote Cleaning

There are “remote” cleaning units available with enclosed rotary cleaning heads that use fast spinning water jets to clean asbestos cement roofing sheets.

Although the operator is remote from the cleaning area, the cleaning is not “remote controlled”, rather, the cleaning head is guided down the slope of the roof by the operator. Provision needs to be made to collect & filter the resultant slurry.

It is important to conduct an initial feasibility study (roof survey) of the roof in question, as some areas of the roof might be weaker than others and these need to be marked out prior to commencement of cleaning, to ensure that the pressure of the water can be adjusted in those areas.

Some asbestos roofs might not suitable for cleaning using this method.

WARNING: Without taking these essential precautions, your asbestos roof could fail and contaminate a property and the surrounding area. Do not leave your choice of contractor to chance – call the specialists now on 0121 709 5352 (Mon-Fri 9:00 am to 5:30 pm)

Once cleaned, asbestos cement roofs should be re-sealed, using a high quality coating system, to prevent rapid re-soiling and more aggressive moss growth.

Surface Biocides

Specialist chemicals are available to kill plant material growing on asbestos cement surfaces.

They should be applied as a low pressure spray or wash.

Over time the moss and algae dies and will simply fall off the roof during rainfall.

Dead lichen crusts are more difficult to remove and should be left in place. Roots of dead mosses may hold loosened asbestos fibres. This waste should be properly collected and disposed of.

Note that the effect of surface biocides may not be fully appreciated for several months – meaning that this method of cleaning is not usually compatible with coating systems, since the cleaning effect takes too long.

Asbestos Roof Cleaning Costs

Asbestos roof cleaning can be expensive, because the health and safety requirements are so strict.

Scaffolding, safety netting, cherry pickers, contaminated waste disposal and other things need to be factored in.

Consequently, it’s wise to consider cleaning an asbestos roof when you’re also looking at re-coating or over-cladding, as the safety equipment will be required anyway.

Occasionally, on heavily contaminated and weed-affected asbestos roofs, a two-stage clean might be required. Whilst this won’t double the cost, it will certainly increase the initial spend on cleaning.

We regret that we are not able to assist domestic customers.


Asbestos Roof Cleaning Considerations

Although asbestos roof cleaning appears to be relatively simple, please remember that there are some important considerations to take into account:

  • If your roof is leaking, it will leak even more during the cleaning process.
  • If you have damaged roof lights, it is good practice to replace them before cleaning the roof.
  • Expect a lot of water and dirt to overflow from the gutters.
  • Most professional roof cleaning equipment is noisy when in use.
  • When working on an asbestos roof, your neighbours will definitely have concerns and will look for reasons to complain.