News on Stone & Slate
Written by Sandy Yeates, Managing Director, Bellstone & Slate Pty Ltd
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A Unique Travertine for Coastal Areas & Pool Paving - High Salt Resistance
Coogee Sandstone - Ideal Summer Surface
Limestone - Dense Durable & Dramatic
Welsh Slate Provides Makeover Magic at Little Bay
Tile Confusion - Buying by the Metre
A Unique Travertine for Coastal Areas & Pool Paving - High Salt Resistance (Nov 09)
We have been searching for 4 years for a travertine that has high resistance to coastal environments and saltwater pools. We have had success! It's a tough ask because salt is corrosive to just about any building material eg metal, concrete, wood or stone.
The issue is durability. Do you want a product to last 5 years or 50 years? We think we have a travertine product that will last a 
lifetime. Our Classico product (pictured right) is unlike a lot of other travertines - it has fewer holes! The holes are also smaller than average. Laboratory testing indicates that this travertine has extremely low porosity and water absorption properties.
Salt damages stone because in dissolved form it penetrates the stone matrix then crystallises. As it does this it expands. The wet dry cycle of stone inundated with saltwater is cumulative. Stone that has natural resistance to the movement of water into the stone structure will have the best durability.
Test results on samples sent for analysis last month reveal that Classico has a resistance to salt attack with an AA rating that surpasses stringent national benchmarks. Classico travertine joins our quartzite and bluestone as one of our 3 most durable outdoor paving stones.
Visitors to our showroom frequently enquire about products that are "safe to use around pools". Usually they are referring to salt water pools because water from traditionally chlorinated or ionised pools is not as aggressive as saltwater. Sometimes, the customer lives by the sea with a north-easter carrying a fine salt spray over their land. Its sensible for people to seek out a stone that has natural resistance to salt because that is what durability is all about.
Classico has an elegent tumbled finish unlike some softer travertines where the tumbling chews out larger sections of the edge. The tumbling process lightens the natural chocolate and caramel colour of the stone but not enough to create glare that many customers express concern about.
The tumbling improves the slip resistance of the surface when wet as well. Test result indicate Classico has a 40X or moderate slip resistance rating. If the pool surrounds will be frequently wet and used by children who run very fast, maybe a stone with a W or V rating might be more suitable. For most outdoor areas with low traffic though a 40X rating is acceptable providing there are no acrobats in the vacinity.
A list of the slip resistance of our stone products can be seen at http://bellstone.com.au/test_results_floorswalls.htm
Coogee Sandstone – Ideal Summer Surface
The soft, sandblasted surface and sandy, golden hues of Coogee sandstone have made it one of Bellstone & Slate’s most popular products for outdoor use. It is being used as wall cladding and as a floor product for covered atria, verandahs and patios.
A recent wet pendulum (slip resistance) test result of 73 (mean BPN) indicates that it has a surface that has a very low risk of slipping when wet. Coogee is light in colour with good heat reflecting and insulating properties – a surface well suited to summer heat loads.
Coogee is available in calibrated form with sawn edges. There are two sizes - a 600x400x15mm tile and 600x400x30mm paver. Sizes and formats not held is stock can be prepared by our stone masons upon request.
Like most sandstone, Coogee is light in colour and porous and may mark or stain in areas where food is prepared or eaten and in exposed locations e.g. near trees where leaf matter or other biological material may accrue. In these situations, it is always sensible to apply a high quality solvent based penetrating sealer that has been specifically designed for the stone.
Limestone - Dense, Durable & Dramatic
Bellstone & Slate Pty. Ltd., wholesalers of premium natural stone products have just released a new black limestone that is stunningly beautiful. It is also a very hard stone with low water absorption properties and high stain resistance.
The product called “Kali” is available in a 600x300x15mm format with a natural split finish that provides a good grippy surface especially in wet weather. The product is ideal for stairs and sloping pathways (see photos below) that are outside and exposed to the elements, as the risk of slipping is low.
Quite apart from its practical advantages, it is one of the most spectacular limestones available on the market and one of Bellstone’s best sellers.
Welsh Slate Provides Makeover Magic at Little Bay
The once magnificent Prince Henry Hospital at Little Bay has undergone a vast transformation courtesy of the NSW Government in a remarkable $400 million redevelopment program that involves the construction of 400 homes, including apartments, villas and terraces as well as retail and commercial development.
The hospital was built in 1881 and featured a slate roof. The original slate was sourced from the famous Penrhyn quarry in North Wales; roofing slates were shipped out as ballast in trading vessels to a colony desperate for building materials that had long life spans.
After 125 years of exposure to salt air, wind and moisture, roofing nails and battens rotted and many of the original slates fretted, especially those slates on the northern side where the heat load was greatest.
NSW, Department of Commerce architects decided to embark on a complete roof restoration of all the old hospital buildings; new slate of identical size, thickness and colour was ordered and supplied from Penrhyn which has now become the largest open cut roofing slate qaurry in the world.
The restoration work is in the final stages of completion as the before and after, photographs reveal.
Sydney based Bellstone & Slate are the Australian distributors of Welsh slate as well as premium quality roofing products from Canada and Spain. Phone (02) 9630 3307 for further information.
Before restoration:
After restoration:
Selecting Stone Tiles Objectively
Using Stone Tile is a beautiful and time honoured way to adorn a home or commercial building but stone by its very nature is variable in colour, texture and quality.
These characteristics make stone attractive as a building component but they can be beguiling as well because the vast majority of people cannot distinguish good quality stone from poor.
The durability of stone is determined by its strength and its capacity to absorb water both of which can be tested for. Good dense, hard stone that has low water absorption properties will be far more resistant to weathering if used outdoors and will be more resistant to salt attack if used around swimming pools. Stone with these qualities will also be less likely to stain, so maintenance costs are lower.
Sandstone is frequently used in outdoor applications such as swimming pool surrounds and recreation areas where the stone may be subjected to salt and chlorine attack from the swimming pools, food and drink stains from BBQ areas and even biological stains from dirt and leaves. The water absorption properties of different sandstones are often assumed to be similar whereas tests reveal huge variation.
The best performing sandstone may only increase its weight by 1% when inundated with water but some sandstone will be as high as 12% - the latter being inappropriate for use as outdoor paving unless repeatedly sealed.
The problem for the consumer is that unless they have experience in evaluating stone it is unlikely they will be able to differentiate good quality from bad. Buying beef at a butcher shop use to carry the same risks – you need to eat it first to assess quality.
Stone like beef battles with a generic price tag that hides a huge range in quality. Thankfully beef is now being tested (Meat Standards Australia), branded and packaged and comes with guarantees and the most professional suppliers of stone are making similar efforts to help consumers identify superior quality.
There are Australian standards for the flexural strength, water absorption, slip resistance and resistance to salt attack for all types of stone including sandstone (ASTM616) – these standards are the consumers best friend providing they can find a supplier that displays recent test results.
Bellstone & Slate P/L are Sydney based stone and slate specialists who routinely test all stone flooring products to ensure product safety and durability. For example, Willow sandstone, their most popular range of sandstone absorbs only 2.2% water whereas the standard is 8%; it is a strong (dry flexural strength 19.4 MPa), dense (bulk density 2421 kg/m3) stone with the highest slip resistance rating (wet pendulum 56V) and excellent salt resistance characteristics (weight loss 0.2% with no visible decay).
Indicative data such as this provides consumers with confidence to use a stone tile or paver for its intended purpose without taking unnecessary risks. Objective information on stone also empowers consumers when making important purchasing decisions.
CSIRO are an accredited testing laboratory for stone and their website provides information on testing www.csiro.au
Tile Confusion - By the Metre
Customers are angry at the way flooring tiles are sold and they accuse retailers of being deliberately deceptive.
This is surprising because tiles are usually flat and square and have tight tolerances for length, breadth and thickness. Moreover, tiles are usually sold by the metre – a unit of area familiar to any builder or home renovator.
The source of consumer resentment is the practice of selling tiles by the covered metre rather than a square metre. A covered metre is the area consumed by tiles fixed to a floor or wall and includes grout joints whereas tiles purchased on a square metre basis represents the tile area only.
In Australia, a 10mm grout joint is the “default” width used in determining the covered area of floors and walls.
As an example 20 floor tiles 200x250mm in size are needed to make up a square metre but only 19.23 tiles make up a covered metre. This means that on a 20 metre project the customer could have either 10 tiles too many or be short that number.
Retailers would argue that the practice of selling stone by the covered metre is the most helpful as it is well understood by the trade. Home builders who are less familiar with the industry practice say they are being short-shifted and that adopting a nominal grout joint width is presumptuous. They cite examples of projects needing only a 5mm grout joint and in some cases, none at all.
Garden and commercial landscaping needs are different again; it’s insane to make assumptions about standardized joint gaps on granite pavers, stackstone water features, sandstone wall cladding and cobblestone driveways – their requirements are quite different.
The dimensions of many stone products do not have the precision of manmade tiles that require narrow joint gaps. Grout joints often need to be wider for some stone products where there is variation in order to align them.
There is no solution to the problem other than very clear and honest labeling when product is displayed in tile shops and garden landscaping outlets.
One of Australia’s leading wholesalers of natural stone tiles, Bellstone & Slate P/L based in Sydney, says they have been aware of the problem and have been selling stone and roofing slate by the piece since 1991 to avoid industry confusion.
According to Chris Jones, Business Development Manager with the company “this practice has worked well for us and for our clients as it has totally eliminated any confusion”.
Salt Attacks Stone
Salt is a notoriously hostile invader of many building materials and stone is no exception. Swimming pools are a seething mass of salts ready to prey on any vulnerable target especially if made more susceptible by shoddy workmanship.
The natural beauty of stone and their safe, non-slip surfaces has created a surge in demand for sandstone, quartzite and travertine tiles and pavers for outdoor projects – but how suitable are they for use around swimming pools?
According to Bellstone & Slate Director, Sandy Yeates, “the suitability of stone tiles for use around pools depends on the quality of stone and there is a big range even within stone types that most consumers are unaware of”.
“Sandstone is very popular for use around pools but the resistance of different sandstone to salt attack when tested in laboratory conditions is quite variable and that is why Bellstone has all its products tested according to Australian standards”.
Mr Yeates said that “stone with high water absorption characteristics and small pore size are particularly vulnerable because the salt moves through the pores by capillary action then crystallises. As the salt crystallises it expands causing sufficient stress on the surrounding structure to cause cracking and fragmentation. Ultimately, the stone frets away causing surface pitting that leaves a fine powdery residue; this is may be accompanied by discolouration.”
“The problems are easily avoided if the stone is tested to ensure it is fit for the intended purpose before laying; it then needs to be professionally fixed and sealed” said Mr Yeates.
If stone is used as coping in modern pools where the coping is frequently inundated home owners need to be very careful. Quartzite and granite are generally far more resistant to salt attack than even the densest sandstone which requires very thorough sealing on all sides.
He said “Bellstone recently sold some fully tested sandstone for a large paving and coping project around a pool in the northern suburbs of Sydney, but after only 6 months, the stone became severely pitted and started to discolour. The speed of the degradation pointed to something sinister but ignoring the signs, the building contractor blamed the stone and defended the sub-contractor who carried out the fixing and sealing”
According to Mr. Yeates, “we had confidence that the stone would perform well around the pool environment because recent test results were excellent. The stone had a good ‘grippy’ surface as evidenced by the wet pendulum slip test (AS/NZ 4456:10-2003A) rating of 56V, so it is a very safe product to walk on when wet. It also had a water absorption test reading of 2.8% - low by sandstone standards. The salt attack resistance tests (AS/NZ 4456:10-2003A) resulted in a weight loss of only 0.4%, so everything stacked up”.
A stonemason consultant was appointed by Bellstone to investigate the project and his damming report on the way the stone had been fixed revealed that:
A corrosive liquid grout had been used contra to label recommendations; as a result water penetration through the joints occurred
No water-proofing additive (eg hydrocrete) had been used with the cement mix to prevent water percolating up through the substrate and into the stone
There was evidence that an acid wash had been used to clean grout stains that had set on the stone surface after fixing
This unfortunate episode illustrates that even the best quality and most suitable stone for use around swimming pools is not immune to careless workmanship.
Mr Yeates cautioned, “It is vital to only use experienced tilers who specialise in fixing and sealing stone according to industry accepted standards – that way the stone will perform well and the home owner can take pride in the finished work”
Mosaics Make it Different
Mosaics are an ancient artform that provides building projects with individuality in a world of increasing sameness.
Hagia Sophia in Istanbul, is adorned by mosaics made from stone, glass, silver and gold. The former church was built in 532AD and is one of the truly great buildings of the world – remarkably it is still standing and hundreds of thousands of visitors each year admire its architecture and art..
Mosaics appear in a number of wonderful Sydney buildings such as the mosaic floors of the State Theatre and the crypt at St Mary's Cathedral.
Mosaic art does is not always grand in its simplest form it can invigorate stone floors, walls and stairs with borders and medallions using matching stone of different colours, angles and sizes.
Stone mosaics can be ordered in one of many netted patterns off the shelf; alternatively they could be crafted by a local artist with a theme consistent with building’s environment and purpose.
Information on mosaic art can be obtained from the Mosaic Association of Australia. Mosaic tiles in natural stone are available from Bellstone & Slate Pty Ltd.
