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Although the specification's title may not be remarkable, the repercussions from it could well be. Its introduction will mean that architects no longer have to wrestle with complex chemical formulae and a library of British Standards simply to find the right product to seal round a window or to prevent moisture entering through a pipe penetration in a wall.

For the first time, architects will be able to approach specifiers with a definition of what they want, and specifiers will be able to select a sealant on the basis of its performance – without the need to understand the product's chemistry.

"For specifiers, it doesn't matter what the sealant is made from, but how it must perform," says Richard Farmer, production director of sealant manufacturer Sika.

The final selection of a product can then be made as a co-operative effort between an informed specifier and the sealant manufacturer.

This new standard, which will apply across Europe now that the UK has adopted it, will allow sealants to be specified on a range of criteria, including movement capability, how easily a material returns to its original shape and how hard a seal it provides.

"To get a sealant used properly is important, and this standard is a means of defining the right product for the job," says David Williams, secretary to the British Adhesives and Sealants Association.

"At the moment, there is a problem with too many people using the wrong sealant – and it costs a damn sight more to reinstall a sealant than it does to buy it in the first place" Williams says. Farmer agrees: "It might be five years after a scheme had been completed before a problem with a seal first appears." The problem is one of awareness. "The biggest single problem with sealants is that they're not sexy," explains Farmer, "and because they are not sexy, there tends to be very little interest in them – that's why there have been so many problems." Sealant manufacturers are already starting the process of reclassifying their products ready for the spring deadline so that specifiers, armed with the new International Standards Organisation specification can buy them.

However, although this standard will address the problem of product specification, it will not necessarily mean the end of problems with sealants. "A big problem is with contractors installing a sealant with different properties to the one specified," explains Farmer – a problem this innovation will do little to alleviate.

1 End use
The first letter in the definition following the standard number (ISO 11 600) refers to the sealant's end use. For instance, glazing sealants for sealing glass into window frames receive a G notation. Facade sealants used, say, for movement joints in walls, are given an F designation.

2 Movement capability
After the end-use letter comes a number that is based on the sealant's movement capability. The number, expressed as a percentage, is the maximum amount of movement divided by the minimum width of the joint.

The standard only covers sealants in the 7.5-25% range. Where movement exceeds 25%, the ISO designation cannot be used to describe the sealant and specifiers need to seek assurance from the manufacturer.

For movement joints, a sealant's ability to recover to its original dimensions – its "elastic recovery" – is important. Sealants that return to their original dimensions are given a suffix E. Sealants with a low elastic recovery are classified as plastic, and so receive a P suffix.

To keep specifiers on their toes, though, sealants with high movement capabilities are by definition elastic, so those products with a movement capability of 20% or 25% will not require the suffix E. But sealants in applications with movement of 12.5% will need to add the suffix to distinguish them f rom products with little or no elastic characteristics.

3 Elasticity
This relates to a sealant's hardness. A high level of elasticity is important in instances where a seal needs to be achieved between materials that move rapidly, for example, metal cladding panels. For heavier components, such as concrete cladding panels, which expand more slowly, a sealant with a lower level of elasticity and movement capability could be selected.

The standard uses two classes for hardness: high modulus (HM) for hard products and low modulus (LM) for soft sealants. These suffixes are used only with the high movement classes of elastic sealants (20% and 25%) because hardness is a significant property in sealants used to seal joints that are likely to move a lot or rapidly, because of the stress this places on the adhesive bond.

In general, low modulus sealants are better. They put less strain on the adhesive bond, which is particularly important if the materials the sealant is attached to are weak or friable. It is also important to specify low-modulus sealants for use in colder climates, because a sealant's hardness increases at lower temperatures. However, where a sealant is to be used in a floor application, or where it could be vandalised, then a high modulus product would be better suited to the task.

4 Substrates
A sealant's designation is based on tests involving three standard substrates: mortar, glass and anodised aluminium. The substrate used is also included in the designation, together with any primers or surface conditioners used in the testing. If the substrate is not representative of the actual materials used, a specifier can then ask for additional tests.

5 Additional requirements
With the basic properties of the sealant specified, other requirements of the application will need to be included, such as life expectancy, colour, adhesion, non-staining, and resistance to fire, water, chemicals and abrasion.

6 Designation
Having determined the requirements for movement capability, the specifier can now write down the ISO designation for the sealant.

For instance, Sealant ISO 11 600-G-20HM-glass, anodised aluminium can be broken down into parts thus: Sealant ISO 11 600 – type – movement capability – modulus of elasticity-test substrates – primer used. Therefore, this designation defines a sealant for glass with a movement capability of 20% and which is quite hard (has a high modulus).