Introduction

Testing……..such a short, seemingly innocuous word. However it embraces so many facets, actions and far-reaching implications. The world today relies on it. Without it we couldn’t go forward. It is a process or procedure that provides an assessment of the integrity of a product or action by some form of quantification and is a direct reflection of our technological advancement and our general levels of performance and understanding. The more products we have, the broader and more complex our technology, the more reliance there is on “testing”.

This paper has been prompted by a recent string of events, testing requests and reviews of testing results generated by local, national and international laboratories. These events, strictly related to the construction industry, reveal an extraordinarily low level of understanding, firstly in the testing methodologies and the generation of results and secondly, and more importantly, the interpretation of the results. There is little point “testing” something without a detailed understanding of why that testing is being done. And for that, or any testing, strict testing procedures and controls must be in place to ensure accurate results - associated with a high level of precision. 

Testing in the construction industry

The construction industry covers a huge range of products, activities, and services that require a vast range of specialized expertise. The industry can be nominally divided into categories that are determined by size, cost and the energy input. Testing is an integral part of all construction categories because for every product there must be some quality control to ensure that it is suitable for its intended application.

In this article the comments on testing are limited to natural stone and any products incorporating or closely associated with natural stone. My involvement with testing has ranged from the simplest identification procedures to complex structural investigations of underground mining situations, to off-shore projects valued at about $60 billion dollars. The level of advice can range from personal advice to extensive geoscientific testing to evaluate suitability of a natural rock or stone product for massive infrastructure development. For example, the correct scientific assessment of an aggregate in a major dam project is paramount because the use of inappropriate (reactive) natural aggregate can have serious long-term consequences. 

Zooming in, the testing in this article focuses on the residential and commercial construction industry where natural rock and stone products are extensively used, albeit often in quantities that are relatively small compared to the rest of the construction industry.

Why test stone? 

Natural stone is used externally in many forms, including paving, decking, steps, pool surrounds, cladding, roofing, funary art, landscaping, fencing, and trench covers. Internally, it is used for wall tiling, floor tiling, kitchen benchtops and other applications, furniture, fireplaces and surrounds, and numerous decorative/ornamental structures. It can be incorporated within structures such as facades, sills, soffits, lintels and cornerstones. Improvements in technology over the last 30 years have dramatically increased the availability of various elements of stone and more-recent technological advances (e.g. internet) have made stone available to anyone from anywhere in the world.

Because of the infinite diversity of applications, coupled with 13,000 possible stone varieties, each of which has different physical and chemical properties, the exact knowledge of how each of the stone products performs is largely unknown. Understanding the stone is therefore a critical aspect in determining its potential functioning and durability in many construction applications. Some engineers require this information in order to design and build structures that utilize or incorporate natural stone. Where several natural stones are used in similar situations the engineer needs to determine the physical and chemical characteristics of all the stones. Just because one stone looks similar to the next to a typical untrained eye does not mean that they perform in a similar way. The natural make-up of stones is incredibly diverse and complex and cannot be guessed from simple inspection. Moreover, the properties can change over a mm scale, over centimeters, meters, and tens of meters. And because stone is three-dimensional its properties can change in different directions, over the same scales. Modify the stone by weathering, deformation or hydrothermal activity and the properties are again affected to different degrees. A very high level of specialized scientific expertise is required to unravel many of the properties of natural stone yet so often technicians are expected to, and do, provide (incorrect) analyses of the situation. The saying that “stone is just stone” could not be more wrong.

From a mineralogical viewpoint almost every stone consists of minerals. Some contain a wider variety than others especially if their process of formation has been multi-stage. Some, such as the obsidian from Armenia consists only of glass and filamentous crystallites. In some (such as basalts, metamorphic rocks and chemically deposited rocks) the mineral grains are so small that they cannot be seen with the naked eye whereas in others (such as spectacular mafic pegmatites from Madagascar and marbles from Australia) some individual minerals may exceed 100mm (some of the largest crystals reach 18m in length, 4m in diameter and weigh up to 380 tons). Just this scale difference leads to an enormous variation in physical properties. Mix the very large and very small together, such as in porphyritic rocks with large crystals in a very fine groundmass, and the characteristics fall into another range.

The minerals themselves play an intrinsic role in the properties of stone because every mineral in building stone has its own physical and chemical properties. Some minerals have strong to no cleavages, which determine strength, others are susceptible to modification by atmospheric reaction and oxidation, such as carbonates and sulphides. Most minerals are unaffected by common solutions but the carbonates (particularly calcitic or aragonitic limestone and marble) are extremely sensitive to acidic solutions and can be easily damaged. Certain clays (such as the smectite/montmorillonite group) are expansive with wetting and drying exerting sufficient pressures on the stone structure of some rocks to cause parting. Despite their high density and strength granites can also contain minerals that display structural breakdown. Depending on the origin and crystallization history of the igneous magma the stone might contain very sparsely distributed minerals that have high levels of radiation the activities of which has destroyed the original mineral structure, e.g. allanite, thorianite and monazite.

What tests should be done?

Although stone is a natural product its characterization through testing is similar in some ways to testing man-made products. Both forms involve failure analysis, engineering design analysis, quality control and all rely on research testing. In man-made products the aim is to produce a product that works in its intended application AND can be manufactured indefinitely to finite parameters from identical starting materials. With stone there is no such thing as having identical properties. For this reason each unit of stone needs to be characterized. Fortunately, most stone of the same type from a similar location in the quarry has properties that fall within a certain range that can be shown to be acceptable for construction, or be rejected.

Testing of stone MUST have a purpose. Testing costs money because it requires preparation (from the natural outcrop, to cutting, and final preparation), expensive testing machinery, laboratory time, and expert analysis of the results. Also, many of the stone tests are destructive and therefore the supply of samples is limited – especially when they need to be shipped in from overseas. And once the test samples are destroyed they cannot be retested.

The use of construction materials is not an overnight issue. The products are usually meant to perform at a high level for many years. So it is not simply a matter of “try it and see what happens and if it doesn’t work try something else”. Additionally, there is often a strong reliance between construction products so if one element fails others might also follow.

There are only about a dozen tests that are routinely performed on stone. Of course, many more tests, similar to man-made materials, could be done but outside of the basic range they would have little practical value. That does not stop laboratories devising tests that are impractical to useless but provide a good income for the laboratory. The accelerated wear test is an excellent example of this. This test deliberately wears down and “polishes” the surface of a perfectly acceptable exfoliated stone surface resulting in non-compliance with slip ratings. The most basic but most informative test that should be done before all other tests is a petrographic analysis of the stone. Such an analysis can only be done by a highly qualified geoscientist and provides valuable information on the mineralogical makeup of the stone, the composition of the individual minerals, the texture of the stone (how the minerals relate to each other), the type and strength of any cement binding the minerals together, the porosity, any structure (is there a directional fabric or systematic microfracturing), degree of weathering (affecting strength) and the presence of any deleterious minerals that could impact on the appearance and performance of a particular stone. Unfortunately, the number of such professionals are very few and getting fewer. My recent assessments of a number of petrographic analyses done by “experts” overseas show them to be of a low standard. But who is to know ?? Clients in Australia also tend to shy away from petrographic analyses because of their poor understanding of stone in general and the relationship of such an analysis to the stone. Laboratories and technicians who do not have access to this level of expertise are also responsible for the decline.

From a historical viewpoint the type and importance of stone testing has changed because of changes in construction utilizing natural stone. Historically, most of the earlier building relied on the stone walls supporting the entire construction. Clearly, there would be limitations on the height of these constructions. A quick survey of many old major buildings, especially official ones, in most large cities around the world reveals that the base courses are typically constructed of massive blocks of stone. With increasing height the size of the stone blocks become smaller. The reason for the large base stones is because the constructions were reliant on the strength of the rock in compression. As construction technology changed from pure stone to one of steel and concrete there was no longer a need to know the compressive strength of the stone because it would no longer be load-bearing. An external facings industry developed because builders, architects and clients wanted to retain the prestigious appearance of stone on their buildings. This required a serious change in the type of stone element to be used. The stone would now be much thinner and be affixed to the building on steel or aluminium-framed structures. Bending strength now became an important parameter and considerable testing needed to be done to determine the flexural strength of the stone. Rather than just occupy the base courses, stone cladding had to contend with a number of new and critical factors that engaged the engineers. At height, there is a substantial wind loading (pushing and sucking) that is also influenced by the shape and orientation of the structure. So tests were needed to calculate the thickness of the stone panel, the size, the anchor strength, the strength of the metal frame both individually and as a whole. In its infancy clashes occurred between the architect (and his vision) and the stone scientist who advised of the unsuitability of a particular stone due to its intrinsic geological and geotechnical characteristics. And so the type of stone became important. To ensure adequate performance for each project, a range of stone needs to be considered for the best properties. But sadly, much of the selection is done on price alone, without due consideration of quality, in terms of immediate and long –term performance, as well as in issues of maintenance. Some clients are sufficiently diligent to allow research on a particular type of stone. For example, in research into beige-coloured limestones for an up-market residence I compiled technical properties and characteristics for 62 varieties, from which only one was chosen.

Levels of testing

The testing of stone is now largely controlled by internationally recognized standards such as ASTM, and more recently, European standards. Some countries also have their own standards, such as China, Japan and Australia. Europe even has mandatory standards and voluntarily standards. The laboratories generally have sophisticated electronic equipment and the laboratories usually employ technical staff that have received some specialized training in the use of that equipment. In Australia, there is an additional tier of control where a volunteer-based national organization (NATA) is in charge of accreditation. But even this is abused because every single test requires accreditation. However, most laboratories that conduct a wide range of tests are understandably reluctant to pay the unreasonably high application costs and annual fees so they apply for accreditation for only a few tests and then use the stamp provided to them to imply that the entire laboratory is NATA accredited (for all tests).

Most of the stone testing is quite basic, involving either the crushing or bending of the stone (to failure), or some non-destructive tests such as water absorption, slip resistance, thermal expansion and petrographic analysis. But situations arise where more sophisticated testing is required, such as X-ray diffraction analysis of certain clay types, radon and radiation analysis, Fourier-Transform Infra-red analyses, SEM (scanning electron microscope), ultrasonic pulse velocity, and resistance to attack by various chemical agents.

A high level of knowledge of all the tests, procedures and results is essential to their interpretation. So too is the understanding of sample preparation. All too often a stone scientist is by-passed in the early stages of a testing programme. Samples are prepared by the client or the stone factory without knowing the exact requirements or with the expectation that the laboratory technicians can manipulate the test apparatus to make the samples “fit”. Once the samples are tested it is discovered that the results vary so much as to render them useless. So a good deal of money has been spent in the procurement of the raw material, its transport, its processing, the transport to the laboratories (especially if there is an air freight component), and the testing. An old colloquial saying that basically says – “rubbish in, rubbish out” is all too true in stone testing. If the test sample is mis-shaped, ridged or cracked a result will be obtained that is much lower than the “true” value. Every test specimen must be examined by a stone specialist or stone scientist to determine its suitability for testing. A lab technician is not trained in stone – they are only trained in how to use the equipment.

Practicalities of testing

It is emphasized that the keys to testing are knowing why testing is necessary, what exactly is to be tested, and then the interpretation of the results as it relates to a certain application. It is fine to have all the testing procedures in place but unless you know and follow the exact steps and procedures for getting meaningful results the testing has no value. For large projects such as the Copenhagen Metro testing can involve field activities because it might be necessary to inspect the quarry blocks that are to be used for the final construction materials. The blocks might need washing down with high-pressure to (a) allow visual inspection of the colour, texture, structure, and any other feature, and (b) to determine the presence of fractures that could compromise the integrity of the stone once it is processed. Occasionally the desired stone is in the ground and therefore partly or fully concealed. Drilling may be required to establish the consistency of texture, colour and structure. However, testing concealed stone by drilling is expensive and may well miss vertical joints, shear zones, compositional banding, karst voids, and zones of alteration. It is rarely recommended.

An excellent, under-utilized, non-destructive geophysical method to determine the presence and attitude of fractures within stone blocks is to measure the ultrasonic pulse velocity. By establishing a base speed of the stone in a laboratory, simple scientific equipment is used to generate a pulse on one side (or end) of the block and detecting the pulse as it exits the block. Various imperfections and fractures tend to reduce the ultrasonic pulse velocity (such as blasting fractures and weathering) and the scientist can predict with a high degree of confidence the integrity of the block, thus saving large transport costs, shipping costs and processing costs should the blocks be flawed. Although cheap and effective, this type of test should not be considered routine unless there is a history and suspicion of flawed blocks.

In most standardized stone tests there is a time element - whether it be the rate of the applied force in physical testing, the length of contact with, or immersion in, liquids, or the number of cycles the stone is subjected to in various tests. Practicalities dictate a finite time for the testing. The time element is clearly a reflection of the mineralogical make-up and other characteristics of a natural material. Unfortunately, in a number of instances this time element is not applicable to all rocks and is therefore a major failing of some of the standards. For example, the salt immersion test has a limited number of cycles (15) that are conducted over a roughly 10-day period. During that time there might be little material loss and the interpretation of that test would be that the stone is suitable for use in a salt environment. However, structural damage that is unseen might have occurred and disintegration could result over the next few months. The conclusion should have been that the stone is NOT suitable for use in a salt environment. Other time related phenomena with stone include: 1) the gradual reaction of carbonate in a polluted environment to produce gypsum (involving a 45% increase in volume), 2) the degradation effects of expansive clay (smectite) in basalts, and 3) the oxidative effects related to sulphides (generation of acids that produce staining and rusting).

One of the more bizarre aspects of testing involves the slip rating of natural stone. Promotions of stone tiles and pavers frequently provide a slip rating, as though it is an incontrovertible, determinate stone property. And most purchasers and users of the selected, tested stone believe this to be true. It is another excellent example of the lack of knowledge in stone because surface roughness is simply the result of a specific mechanical process that can be modified as to the requirement of a particular application. It has nothing to do with the properties of the stone !! A specific slip rating can be applied to ANY stone.

Deceptive behaviour in stone assessment and testing

Despite having quarries and factories that provide good stone samples, the availability of many standards, and good laboratory conditions capable of providing accurate results, one of the biggest problems in the stone industry is fraud. The reasons are basically 3-fold, namely (a) greed, (b) almost total lack of knowledge, and (c) we are dealing with a variable natural product.

Wherever good money can be made with little effort the scene is set for an obvious attraction to fraudsters and dishonest people. The stone industry is a great example. A short and probably failed period in various aspects of the stone industry is sufficient for these dishonest people to recognize the financial openings. Having discovered that there is such a lack of good knowledge of stone in the community, coupled with natural variations in the stone, and the absence of any control, they enter the construction industry and pose as experts in this poorly understood specialist field. A little technical knowledge and gift of the gab is all it takes to persuade most people to accept their advice and undertake useless tests that will provide little or no useful information but will relieve them of considerable money. It is very difficult for the general population to check the bona fides of these tricksters but in commercial projects there should be sufficient awareness within an organization to run some checks before engaging these people. However, the people doing the checks do not have the required expertise to do so.

This fraudulent activity filters down to the retail industries where finished stone products are sold.

A retailer displays a wide range of stone. He provides advice to an unknowing public. But from where does he get information about the stone? Is it accurate? Usually NO, but he has that additional modicum of knowledge that he has picked up by being in the industry and is able to provide the dubious advice and convince the buyer. The retail supplier is in no position to become an expert in the field of stone, the wholesale supplier is in no position to provide expert advice, and even most quarries don’t know much about the stone that they are quarrying. It is also interesting to note that some suppliers do not want to engage a stone scientist if they intend doing wrong, and some suppliers of stone do not want the stone tested to cover the inadequacies of their product. Some suppliers even exert sufficient pressure on the client and builder to get rid of a diligent stone consultant if he finds potentially deleterious irregularities with the stone quality or with supply. Personal experience !! Wherever big money is involved powerful forces may be at play. Others will attempt to manipulate the testing by various means. For example, I was asked to do stain testing of a light-coloured, Italian, effusive rock that the supplier wanted to get into a high-end project. The “pristine” tiles that were supplied were multiply coated with an invisible penetrating sealer on all sides to try to minimize staining in the hope that that the attempted fraud would not be discovered. It turned out that the stone was so porous and susceptible to staining that the stains from common food products eventually penetrated through the 15mm thick tile. The tiles also contained an abundance of sulphurous substances that gradually caused the formation of a sulphate (thaumasite) and massive surface disintegration over a period of a few months. This could have been a disaster for the developer and client.

It must be strongly stressed that a supplier is there to supply stone to a buyer and to take his/her money. That is all. Most of the stone advice from a supplier is questionable and any additional advice for stone-related products is usually derived from a third party (e.g. sealer salesmen) and is equally questionable. Does the supplier have the scientific expertise to provide advice? Has the supplier time to conduct properly controlled testing? Is the supplier likely to engage an experienced stone scientist to evaluate the testing data when there is a likelihood that the testing has not been properly carried out and might impact negatively on his sales? Of course not !

Unfortunately, fraudulent/deceptive activity is very common in the supply and testing of stone. Samples can be manipulated and results can be easily concocted and modified. For example, a client wants a particular type of stone from country X. He wants the stone tested for a range of parameters in order to properly engineer the construction. He requests that some stone be taken from the quarry, processed into the required units, and tested. But who is there to supervise that the stone taken from the quarry will be similar to that which will be used in the construction? It is common practice for the quarries to set aside “superior grade” blocks for clients to view, and for testing. That stone has probably aged and is clearly much stronger than a newly quarried stone that retains its quarry sap. In most countries where stone output is high there are companies that co-operate to supply a similar stone. For example, a middle-sized order is received by a European supplier that supplies a particular, good quality beige-coloured limestone. But at that time he might be fulfilling another order, or there might be a breakdown of equipment, or other reasons that prevent him from supplying. So he simply rings up a nearby supplier whose stone looks similar but is of lower quality and cheaper. They conspire to supply the stone under the name of the primary stone. Should the end user question the quality of the stone he would be told that it is a natural product that varies. Who is to know ?? Several years ago prestigious high-rise units in a city used a pinkish-mauve, dense limestone from northern Italy on the floors in most rooms. Within a short amount of time in all the wet areas, the stone commenced spalling and pop-outs were common. When contacted, the Italian supplier responded that it was totally suitable for apartment floors. True. But when asked about the suitability should the stone become wet, the response was that I did not ask about that previously.

When testing stone for the compressive strength (or comprehensive strength as some suppliers call it on their website) it is necessary to test samples in a dry condition and in a saturated condition. Both results are necessary because there are some sedimentary stones that have a 70% reduction in strength when saturated. However, it is not uncommon for European suppliers to provide you with only a dry strength result. In fact, when obtaining the testing schedule for one project it was noted that they tested 20 cubes in the dry condition and only quoted the single highest value.

Have you ever opened a reference book displaying beautifully presented photographs of stone?

A few of these books will provide technical information on the reverse side or at the bottom of the page. Have you noticed that nearly all the technical information is the same for every rock type? This misrepresentation can be extended to numerous websites where false information about the stone is widespread. I have also encountered the substitution of results that have been taken from files for stone tested much earlier. How many people would notice?? Most labs know that they can get away with this kind of fraudulent activity. Easy money. Never tell a laboratory what you think the answer might be. For example, a lab in Australia was advised that the result for a water absorption test should be around 0.40%. Strangely enough the results that were returned were 0.39%, 0.40% and 0.41%.

Several years ago at this stone fair a premier stone company from Italy was distributing superb, colour, fold-out, glossy brochures of their stones from various parts of the world. On the back page they presented the technical specifications. Of the 40 brochures I found only one (yes just one) that had technical information that was internally consistent, accurate, or with the right units. Again, how many people would know? Only a very experienced stone scientist!

A lot of unnecessary testing can be avoided by using an experienced stone specialist or stone scientist. It is unfortunate that these individuals are few and far between. As a specialist you need to know what you are testing, what you are testing for, and then how to interpret the values for your particular purpose. Most people who request tests don’t know anything about testing and the meaning of the numbers generated by the laboratory. For example, the construction of a luxury waterfront residence called for a high quality limestone. The architects engaged me to examine the test data from the supplier. Unbelievably, the test results (from a prominent laboratory) came back (signed and counter-signed) stating (just 7 times) that the stone had a bulk specific gravity of just 0.99. With the specific gravity of water being 1.0 it means that the dense limestone (with a real SG of around 2.71) will float on water. The architect noted that this was good for any impending sea-level change due to global warming.

Another example of manipulated testing centres around something that is not visible – natural radiation and radon content in stone. To promote the plastic countertop industries (both Corian-type products and engineered, polyester-based stone) there have been well-funded misinformation campaigns to undermine the natural stone industry by claiming that natural stone is dangerous to children doing homework on the stone surface and dangerous to pregnant women. To prove their point a pegmatitic stone from Brazil was taken to a particle physicist at a US University in Houston for testing. An uncommon mineral that had crystallized in late-stage fluids within this unusual rock type was exposed at the surface and emitted radiation levels that could be detected. Had that mineral been in the body of the countertop there would not have been much of a reaction. Similarly, there have been scare campaigns on the occurrence and effects of radon in dwellings. Sure there is radon, but most of it comes from natural sources under the dwelling or from surrounding soil, fill, rock or other building products. Of added importance is that the accurate testing of radon is a highly sophisticated procedure (see henselgeosciences.com.au/articles), not a do-it-yourself test kit.

Erroneous assessment and testing of stone

There are many examples where testing of stone has been undertaken, ostensibly without fraudulent intent. Some universities or research laboratories that have engineering facilities may choose to gain additional income by using their equipment to test stone. But without a good knowledge of stone, mistakes are made right from the beginning (sampling and processing of the stone) through the testing procedures, to the calculations of the results. In natural stone there are orientation effects, textural, mineralogical and structural details that must be taken into account. Then there are processing details that are very important, such as a lack of flatness, ridging and bedding orientation. Ridges will cause point loading and the true results can be reduced by up to 90%. Similarly, any fractures within the stone, prominent mineral cleavages, or mineral segregations can cause lower results. Laboratory technicians do not understand these geological features and their significance in relation to the testing. They only know how to use the equipment used in the testing. Never make a lab the first point of contact for stone testing. I have observed tests performed on stone by some in-house laboratories, especially those operated by councils, following standards that are applicable to bricks, ceramic tiles and clay pavers. These tests are not appropriate for stone and creates considerable confusion, especially when engineers are involved.

As mentioned previously a lack of stone knowledge can lead to bad assessments and considerable unnecessary testing at substantial expense. This was demonstrated recently in a large foyer paved with basalt. The vesicular basalt was covered in a whitish film that was not acceptable to the client. The company inexplicably engaged an environmental lab to determine the cause and provide a solution. After weeks of testing and tens of thousands of dollars the lab could not determine the cause of the whitening. On seeing the floor it was clear after just 5 seconds that the cause was due to sand blasting and an embedment of rock flour into the vesicles. An even more expensive test programme was undertaken on a European limestone by a consultant with little stone knowledge directing an overseas lab to determine the cause of surface spalling. Using sophisticated equipment the lab technician concentrated on salts as being the cause when in fact it was due to pockets of expansive clay. This was recently followed by another situation where a limestone floor was believed to show moisture. The “expert” engaged has negligible stone knowledge and could not differentiate between natural textural variegation and moisture and suggested almost total replacement. He also recommended replacement of external limestone paving that is showing water staining. The paving is abutting lawns that are watered daily as is the overhanging shrubbery. But as noted above, who would know if an experienced consultant was not engaged. This type of fraudulent activity by a few non-experts is all too common in this unregulated industry.

Paving is another area where incorrect assessments of problems are very common. There is a surprisingly high incidence of drumminess in stone paving world-wide, especially external paving. Some of it is due to properties of the stone (e.g. expansive clays, abundance of platy phyllosilicates, high porosity, stress) but the majority of the problems are due to workmanship and inappropriate selection for particular applications. Successful paving design needs to be individually tailored for each situation because of the large number of variables. Unless those variables are properly addressed (especially the type of stone) the chances of paving failure are high (Hensel 2007). It is always amusing that the most common construction element that is blamed and tested is the underlying concrete. Interestingly, the assessment of stone paving failures are nearly always done by engineers (who know very little about stone) rather than a stone specialist or stone scientist.

Misinformation

As a result of several site visits it has come to light that usually well-respected European manufacturers of construction materials disseminate misinformation to many readers who believe that this information is factual. This just spreads and perpetuates incorrect information through much of the construction industry because of the huge exposure of their products. Because these companies praise themselves for their expertise in construction using their construction products (such as adhesives) and widely advertise the fact that they conduct considerable testing and research in their laboratories, any output from these companies is taken as gospel by the users. But is this output ever checked ?? Apparently not ! If the authors of this output are incorrect in what they write imagine the impact it has on the mass of users. Statements that stones are “sensible” to humidity and that travertine is highly porous, slate is full of clay, and where the distinction between matrix and groundmass is unclear is not helpful and causes dispute. And who do the users believe – these companies, or an experienced stone scientist?? But nothing beats the hype and marketing (and misinformation) put out by the companies selling sealing products for stone (see henselgeosciences.com.au/articles).

Workmanship

Finally, it must be strongly emphasized that any amount of testing of natural stone cannot predict the durability and behaviour of stone where bad workmanship is involved. It is easy to “butcher” even a good quality stone and it is also not possible to turn a bad stone into a good one by miracle cures out of a bottle. I refer here to the response that I receive regularly from architects and interior designers who, when warned about potential stone failure, say “oh, that’s OK – we’ll just seal it.”

In conclusion, although this talk has been mainly negative and focused on a few of the problems and short-comings in the area of stone assessment and stone testing it must also be emphasized that the builder, client and architect should not give up on natural stone. There are so many advantages in using natural stone and with the huge variety that is available there will be a stone that is suitable for a specific application. All that is needed is some guidance by the right advisor.