:: Certification of Stone - Common Sense or Insanity?

by David West - David is the Executive Director of Architectural Conservation at International Conservation Services in Sydney.

You've spent the past year working with the designers of a prominent building to help them choose suitable stones for the facade, the entry lobby and all the bathrooms throughout the building. The designers, and their client, have been most particular about the effect they want to achieve, and you've submitted many samples, visited them monthly, and even spent several days chasing unusual materials in Europe, Asia and North America.

Now the job is finally out to tender, and you've just received the documents from the main contractors pricing the project. You've opened the specification to the stone section, and you're delighted to see that all the materials specified by the designers are those that you gave them samples of. Even better, you are nominated as a source for all of those materials. Then you see a clause like this: "Certification - provide certificates for all stones according to one of the following: a) XYZ to certify all stones b)stone supplier is to certify all stones as fit for purpose c) all stones to be certified by a NATA laboratory"

You've never seen clauses like this before, and what's more, you've never seen certificates for stone before. What on earth does this mean?

Thinking for a minute, you realise that you know about Standards Australia and ASTM and BS and CEN - and you know that they all write standards for testing of stone and standard material specifications (Ed: see http://www.asaa.com.au/standards.php and discovering Stone issue 3, p.58-60). And you've heard of NATA before, and understand that they have something to do with laboratories involved in the testing of stone. And you've had stone tested for projects before. You've used several different laboratories at different times, including Amdel and CSIRO. But you've never heard of stone being certified, and you've certainly never heard of XYZ.

You get on the phone to the designers, and ask them what this clause means. They tell you that they subcontracted the writing of the specification to a specifications consultant, and that you'll have to ask him. You call the specifications consultant, and he tells you that because of the number of problems that have been encountered on projects with the supply of stone that doesn't match the specification, there is a move in some parts of the industry to require that stone be certified. He thinks this is a good idea, because it will help builders and architects to make sure that the stone that is supplied and installed by the subcontractor is the same stone that was specified by the architect and selected by the client.

Now, you know about the problems with stones being substituted, and you've seen some real disasters with stones that are far too soft being put into office lobby floors, or stones that are way too porous being used in bathrooms. And you know that sometimes, even with the best of intentions, it is difficult to resist the pressure from a designer who loves a stone and wants to use it in the bathroom walls even though you've told them that there is a big risk of it staining when used in a wet area.

So part of you thinks this certification thing might be a good idea.

But on the other hand, you also know that every project is different, and every stone is different. And you know how the same stone can change from year to year (sometimes even from month to month, depending on how consistent it is). And you've regularly had stones tested in order to satisfy the concerns of a project designer or engineer, only to find that the results are very different to the information you had on file for that stone (and which sometimes was only 5 or so years old).

So just what are these certificates going to do? After all, the designers have already selected and specified the particular stones they want. And you know that they are suitable for the various applications, because in each case, you've recently used the stones on other projects, and so not only do you have some test reports from those projects, you've also been able to see how they perform in use over the past few months or so.

The answer is, not very much. All it will do is give the designer and the builder a small amount of confidence that they will get stones for their project that conform with the requirements of the specification, and that will perform satisfactorily in the locations that the stones are installed.

Of course, the certificates won't mean that the stone does actually conform with the specification - it is the test reports and the samples submitted for testing that will determine that. Test laboratories are familiar with the possibility that the sample submitted for testing might just happen to be taken from the best of the material rather than the worst (after all, there is a 1 in 10 chance that the sample will represent the best 10% of the stone just as there is a 1 in 10 chance that the sample will represent the worst 10% of the stone).

Nor will the certificates mean that the stone will actually perform in use - because the certificate will be based on somebody evaluating the results of some tests on a sample and deciding whether these results suggest that the stone will perform in use on a building that you cannot yet determine what the usage pattern will be. If you think that sounds like black magic, then I'm afraid that I have to agree with you.

In a nutshell, I'm not a fan of requests to certify stone. After all, most contracts require the provision of a warranty, and that covers the purchaser in the event that you supply material that is poor quality and doesn't meet the specification. If the designer has selected a material that is not suitable for use, then it is your responsibility to inform him of this prior to supplying the stone - otherwise, you will leave yourself open for claims.

So, what can you do? Quite a lot, actually.

You can get your stones tested to provide good technical data to assist in the evaluation of their suitability for use in various applications.

You can ensure that the samples that are tested comprise pieces of stone across the spectrum of the quarry, so that you get a range of results for each test method, thus showing how variable each stone is.

When you have the stones tested, you can make sure that the tests are carried out according to recognised standard methods, such as the ASTM, EN or AS standards.

You can use laboratories that have experience with dimension stone testing, and know how to carry out the standard test methods. You can pick laboratories that have a QA system in place. You can pick laboratories who have had their QA system independently audited. There is even an international standard for laboratory competency (ISO/IEC 17025), so you might look for a laboratory that has been independently audited to this standard.

Finally, you might choose a laboratory that is NATA accredited (see sidebar) for the tests that you are having done, but remember, in Australia the only laboratories that have any significant accreditation for dimension stone tests are Amdel Limited in Adelaide and Boral Resources in Sydney. Other recognised laboratories with good experience in testing of dimension stone, such as CSIRO in Melbourne, and Stone Initiatives in Adelaide, are not NATA accredited for any dimension stone tests. They have considered gaining NATA accreditation, but believe that external auditing for overall laboratory competence and maintenance of an appropriate QA system is more relevant.

Going back to your project with the specification, in this instance you could trust your experience, and on the basis of the tests and past performance of the stones specified, you could write a letter as the supplier, 'certifying' that the stones are fit for the purpose they are going to be used for. After all, you've spent so long working with the designers that you wouldn't have let them choose something unsuitable, would you?

David West is Executive Director, Architectural Conservation, with International Conservation Services in Sydney. He is also a Director of the Australian Stone Advisory Association, and is the nominated ASAA representative on Standards Australia technical committees relevant to the stone industry. u

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