Natural stones in India have been used in heritage structures since time immemorial. The Taj Mahal in Agra is an iconic example of white marble laid with semi-precious stones. And, the legacy of these stones have continued, with only their usage being limited to heritage structures, but modern construction as well. Glossy or matte, patterned or coloured, natural stone for modern structures offers the customer the gamut of aesthetic options. But to get the best from the stone of your choice, it must be treated properly. Arshaan Anees, National Head, Tenax, explains the science behind the treatment of natural stone.
Treatment of stone refers to the numerous processes followed, such as grinding, resining and polishing to make the stone attractive. The main types of chemicals used for the treatment of natural or raw stone are epoxy resins and polyester resins (mastics).
There are three steps involved in the treatment process. First, the natural stone is cut into slabs. This is done based on the thickness required by the client and the application. For instance, stone used on a kitchen counter needs to be slightly thicker. This is followed by the grinding process and is carried out with the help of diamond coated polishing tools that are very strong. For example, granite is the second hardest stone after diamond. Next is the resining process, which means application of the epoxies. Epoxies are a type of strong adhesives used for bonding and covering surfaces; typically bicompoenent products that need to be mixed together before use. Epoxies provide strength to stone, which can be vulnerable to breakage after the cutting process and can be damaged while lifting. They also hide natural defects in the stone such as cracks or damages. Through resining, the epoxies microscopically enter the stone and hold the particles of the stone together. They also help enhance the colour of the stone for a better visual appearance. Next, polishing is carried out, which gives the stone its shine. In this stage, the layer of epoxy is removed from the stone´s. This is done using different types of polishing tools based on the final finish desired by the client. Hence, different polishing tools are utilised to obtain different finishes: silk, matte, honed, caress or glossy. The entire process is carried out in the factory.
After the laying of the stone is carried out in a particular project, the client may want a sealer to ensure nothing penetrates the stone. Surface treatments are available for this and these are more like ´care´ products.
Mastics are polyester-based glues used on site after fixing the stone.
Akin to a ´final touch´ product, they are used to fill defects, cracks or holes. Mastics are available in different colours and one can mix and match depending on stone´s colour.
Affordability and pricing
These chemicals are available at most hardware stores across India and contractors are well aware of their benefits. They are not cheap but are competitively priced, with costs on par with most international suppliers in the market. Locally, there are not many companies in this business. However, these are affordable as the target audience includes big construction companies as well as small players.
These chemicals are used for a wide range of natural stone that can be used in flooring, kitchen counters, designer artefacts, wall cladding. Some glues can be used for joining different surfaces such as stone to stone, stone to wood, stone to glass, stone to steel. Waxes can be used for maintaining the shine and gloss on the stones. Surface treatments can be used to prevent staining and discolouration of stones. Many projects across India, including Bengaluru and Mumbai airports, Wipro, etc, have made use of natural stones processed by these chemicals.
A boon for stone
Once the epoxies are absorbed into the stone, it lasts a lifetime. However, before application, all chemicals have a shelf life of about two to three years.
The Indian boom
Currently, the Indian natural stone industry is booming. Stone´s such as marble and granite are in high demand owing to construction projects on the rise. Hence, the demand for these chemicals will also increase. Looks like a boom-boom situation for epoxy and mastic manufacturers!
¨Being the only company in Asia, which has a fully integrated natural marble processing unit of Breton, Italy in Silvassa, Nitco Marble has been using resins since we started our plant in 2010. Resins benefit in terms of automatic line adaptability and after processing characteristics along with the best nutrition and strength to the marble stone. It is excellent in all three major concerns of the marble industry: Block strengthening consumables, back side strengthening resins and net and top side filling resins and polishing.¨
- Arun Sharma, Vice President Marble Operations, Nitco Ltd
Cautions for heritage structures!
¨While chemicals such as epoxy are being used for the treatment of stones in modern construction, this does not apply to a heritage structure. In heritage structures, the only permitted coating for stones is liquid silicon. Also, stones like marble or granite do not require coating as they do not absorb air and moisture. One unique example here is of the Taj Mahal in Agra. Five hundred years, and the marble has lived without any need for coating. If anything has impacted the structure at all, it is pollution! However, as chemicals like epoxy have their own colour, which to an extent can affects the natural colour of stone, today these are popularly used in modern structures for the aesthetic look they offer.¨
- Chetan Raikar, Chairman & Managing Director, Structwel