StoneSir Inc.
A LEADING MANUFACTURERS AND EXPORTER OF GRANITE PRODUCTS.
Choosing and using Natural Stone (PART 4)
TRAVERTINE
Travertine is the name normally given to a type of precipitated calcite associated with the cooling of waters around hot springs or in caves. Being formed very slowly it often incorporates dead matter such as tree debris that later rots away to leave a voided structure.
The performance of travertine greatly depends on the size and density of the voids, which, in most instances, are routinely resin surface filled before the finished stone is supplied. The nature of the fill material must be compatible with the travertine and not subject to discoloration or decay.
Traditionally travertine was naturally bedded and generally referred to as vein cut. Recently travertine cut face bedded and referred to as classico has appeared on the market. Whilst the vein cut material has a long and proven history of use, the cross cut or classico travertine has not yet proved to be as suitable because of surface collapse and filler failure. Before this material is considered, its limitations in performance must be taken into account.
Generally travertine is suitable only for internal flooring purposes, and then only after the most careful consideration. Strength may be lower than most other stones and the presence of hidden voids below the surface may lead to ongoing repair when the filling material collapses.
Unfilled travertine has been used for flooring purposes but only after strict quality control of the size and distribution of the voids. All travertine is imported.
GREEN MARBLE OR VERDE
Green or verde marble is considered separately to true marble because its origin is often the result of the metamorphism of rocks other than limestones. The green colour is typically derived from the presence of serpentine minerals. These minerals are relatively soft and the structure often weak, the stone commonly requiring reinforcement from matting glued to the underside.
Verdes are rarely used for whole floors and are preferred for providing coloured inserts to other flooring materials. Care must always be taken to ensure their compatibility with other stones.
A special consideration for any verde is the presence or otherwise of asbestiform minerals that may be naturally present e.g. chrysotile (white asbestos) and the amphiboles tremolite and actinolite. It may be prudent to establish that, where present, fibres of these minerals in the respirable range are not generated during any cutting, grinding and polishing operations, particularly if carried out dry.
The Asbestos (Prohibitions) Regulations have banned the import, supply and use of blue, brown and white asbestos (crocidolite, amosite and chrysotile respectively) essentially when part of an asbestos admixture product. Natural stone that contains chrysotile for example, and is used for flooring, would not be classed as an asbestos admixture product.
