Non-asbestos alternatives to asbestos cement began to be introduced to the UK market in 1984, but asbestos cement products continued to be supplied into the UK market until 1999.
As such, any product that appears visually similar to asbestos cement that was supplied prior to 1984 will almost certainly contain asbestos, but any product used between 1984 and 1999 could be an ACM.
Unless an identification mark is present on the product, it is not usually possible for a layman to identify whether a sheet contains asbestos or not, and in many cases even an expert can not tell without finding the mark or having a sample analysed.
With slates, the mark was ink jetted on to the back of approximately one in twenty products, with the same letters denoting whether they contain asbestos or not. Finding these marks can be a problem.
With the above in mind, a quantity of slates will need to be removed before the mark is found, and so unless you have good reason to believe that they are non-asbestos they should be treated as an asbestos cement ACM from the onset.
For roofs fixed after 1984, when the slates could be asbestos cement or non-asbestos, looking at the original specification may help, however it was common at this time for a number of specifications to be changed by the roofing contractor. Because asbestos cement slates were cheaper than their non-asbestos alternatives, the roofing contractor may have opted for using asbestos cement slates without notifying the client and the designer of this change.
In this situation, it is recommended to carefully remove a small sample of the product (see asbestos removal) and have this analysed by a competent laboratory. If constraints do not allow this, then the material should be assumed to be an ACM and treated as such.
In addition to the above problems, unless the roof was built fairly recently, it is highly likely that it will be dirty and covered in moss and lichens, unless it has been well maintained. This is a problem which will once again make finding and identifying the manufacturers’ marks of products such a tricky task.
It should of course be remembered that when accessing the roof to check for the mark, that both asbestos cement and un-reinforced fibre cement sheets are very fragile. All operatives must be provided with protection to ensure that they cannot fall through the product and subsequently injure themselves; a far more immediate and serious risk than the risk of catching an asbestos related disease.
Identification of asbestos in profiled sheets is not a great deal easier, either; although the sheets should carry the indent on the overlap roll, this did not always happen, and even if there is an imprint, this may simply be too difficult to read.
The manufacturers’ mark on profiled sheets is indented into the overlap of the side lap roll. Usually in code form, the name of the manufacturer, the date of manufacture, the shift and possibly the machine it was made on will be provided here. If the product contains asbestos, then the manufacturers’ mark should include the letters AC; similarly, if the product is non-asbestos, then it should contain the letters NT.
In the mid 1990s, some profiled sheet manufacturers started to inkjet the underside of their sheets with the production mark.
For other moulded products, the position of the mark will vary, with some having no mark. Where there is a mark, the same lettering applies.
Very few flat sheet products will have any marks.
If you’re looking to find out more about Friable and Non Friable Asbestos, you can find information here: What are the Differences between Friable and Non-Friable Asbestos?