FAQs – frequently asked questions
To share our field experience there is no better way than listing the most common questions we receive from the slab producers who are exploring the possibility of investing in a Resin Line.
“Is it really essential to dry the stone at the beginning of the treatment? If so, how to?”
Absolutely yes! The complete drying of materials is always crucial. For the drying of the stone to be thorough the time, ventilation and temperature factors have to be managed with flexibility. In fact, the water absorption rate varies according to material; and therefore the drying method will change according to the peculiarities of the stone to be mesh backed and resin coated. Companies dealing in highly porous materials which have a high absorption rate such as travertine or “exotic” granite, should keep the slabs in the drying oven for a long time (up to 90 minutes) with intense air flow at elevated temperatures. Drying most types of granite is not difficult, given their compact nature and low absorption rate. Accordingly, granite processors can leave their slabs in the oven for just half an hour at 45 C°. Onyx slabs can be seriously damaged by heat. Aware of that, responsible stone processors will compensate a lower temperature with greater air flow, and keep the slabs in the oven no less than one hour.
“Can I use second-rate resin to mesh reinforce my slabs? After all, the back will not be visible after installation.”
One of the biggest and most common mistakes made by inexperienced stone processors is trying to economize on mesh backing. Contrary to what many people may think, the reinforcement of delicate stone depends on proper mesh backing and only partly on resin coating, and for this reason we recommend using good quality appropriate fibreglass and resin. Nevertheless, there is simply no need to attach the mesh with very expensive non yellowing resin, unless we are not talking about the reinforcement of translucent onyx and quartzite.
“Is it true that the slabs should be always honed before resin application?”
So many beginners face a dilemma whether or not to hone their slabs. Furthermore, honing is too often confused with calibrating. Despite the two terms are interchanged by non-experts, they are not at all synonyms. The subject is far too vast to cover adequately in just a few sentences. Yet we can provide our readers with an overview of cases. Generally, granite slabs should be honed because granite cutting machines (no matter if they are traditional gang saws with steel blades or the latest multiwire systems) produce rough surfaces. Whenever perfect flatness is a fundamental performance requirement (e.g. realization of granite kitchen countertops) granite slabs should be calibrated too. Marble processors who use efficient diamond-blade gang saws can obtain top-quality slabs without any honing (unless they work certain stone with defects which are made easier to resin fill through honing). To produce “transparent filled travertine slabs” surface honing is a necessity. The repair of broken slabs of coloured marble, traveronyx and onyx involves a non-stop production cycle including mesh backing, surface restoration, honing and application of a layer of coloured epoxy (resin colouring is important to hide stone faults).
“How to choose the right resin supplier?”
At S.E.I. we have a code of conduct that outlines principles and ethical commitments. One of the rules we give ourselves, is that we cannot promote any resin producer to the detriment of the others. Notwithstanding, we endeavour to take all reasonable steps to protect the interests of our customers, and we have no hesitation in pointing out the inadequacy of a specific type of resin.
“How much resin should I use to treat one slab?”
The true answer is – it depends! It depends on the characteristics of the stone and on the conditions of every slab. Moreover, the various types of resin have different performances. It may happen that slabs very much alike can be restored with 600 grams of one resin, while one kilogram of another product is barely enough. In order to avoid errors, the resin application should be subdivided into various coats. The treatment of badly cracked material with high resin absorption rate involves longer breaks among the retouches, to allow the workers locating cracks which remain open and adding further resin.
“Do I really need a vacuum chamber?”
There are so many conflicting opinions and different ideas on this subject. Some people think that the impregnation under-vacuum is necessary, while others are sure that it is of little or even no importance. From our point of view, a vacuum chamber which meets certain criteria can make the difference in the treatment of various materials. For example, the vacuum technology is an effective means to force the resin to get into the deep hairline fractures which weaken much beige and cream marble. As well, an efficient vacuum chamber represents the solution to an age-old problem for granite companies: the presence of microcracks on the surface of polished slabs. All the same, meeting the strictest quality standards without vacuum machines is possible. Indeed, there are true masters of Resin Treatment who do not under-vacuum impregnate their slabs and yet they are able to restore and strengthen seriously faulty stone. On the other hand, it is worth noticing that these specialists only use best quality resins, know how to prepare mixtures of resin and pigments, never skimp on the quantity of resin or on resin application time. Now the question is: how easily can a company interested in a Resin Line find workers skilled and experienced enough to do the same?
“Is it possible to repair slabs which broke into pieces?”
The basic presupposition of the Resin Treatment of stone is that any material can be turned into sound slabs of good appearance, no matter how badly cracked it is. Nonetheless, there are only a few specialists able to fix shattered slabs, who aside from boasting decades of experience in Resin Treatment are driven by a true passion for their job. We are always striving to explain to our customers that if they really want to learn Resin Treatment, then it is just a matter of time until they succeed in “reconstructing” broken slabs of valuable materials like Portoro, Giallo Siena, Rosso Damasco or White Onyx and in “restoring and filling” the surface of travertine or traveronyx. However, we must make very clear that companies planning to reconstruct, restore and fill unsound slabs on a large-scale will have to establish a proper stone repairing unit complete of specialized machinery and equipment.
“How long does resin take to harden?”
Nowadays, there are hundreds of different types of resin. Indeed, the resin producers are forever developing new resins and catalysers to increase the range of stone which can be treated as well as to speed and streamline the production process. It is essential to allow each resin to harden according to the time specified by the manufacturers and to use it in accordance with its intended purpose. Some examples may clarify and underline this concept. To “transparent fill” travertine slabs we should use one of the latest high viscosity epoxy resins which harden in around one hour when exposed at temperatures ranging from 35 C° to 40 C°. White or pink onyx slabs should be coated with low viscosity non-yellowing resin and kept in the curing oven for 3 hours at 30 C°. To enhance the blue colour of Ukrainian labradorite it is possible to either use an epoxy resin which hardens in a couple of hours at 45 C°, or better a slow-curing resin which ensures excellent impregnation providing that the slabs are left in the oven for no less than 4 hours.
“Can I polish my slabs as soon as they go out of the resin polymerization oven?”
In the past few years there have been many attempts to develop technologies aimed at making it possible to resin coat and polish the slabs without breaks. This is why there is much talk about radio frequency ovens which would cut the resin curing time dramatically (from hours to minutes). The truth is that there is nothing innovative about these systems, as by the mid ‘90s S.E.I.’s founder had already patented a microwave oven for the treatment of stone with synthetic resin. Some readers may wonder why we never advertised this technology. Well, it’s all a matter of expectations of treatment prospects. Using ovens designed to force the resin to harden in a few minutes, means to prioritize quantity over quality; and in our opinion that makes no sense. Indeed, the internal temperature of radio frequency ovens is so high (60 C° to 80 C°) that onyx slabs get irreparably damage. Extreme heat can spoil much marble, limestone, quartzite and exotic granite too. What’s more, the resins which are compatible with radio frequency ovens tend to yellow more markedly than any other epoxy product. Therefore, it is totally inadvisable to process light-coloured stone with microwave or macrowave resin plants. It is also important to note that radio frequency ovens negatively influence the resin penetration capacity, as their high internal temperature causes the resin viscosity to rise in the blink of an eye. As a result, deep narrow faults cannot be saturated with resin. Our conclusion is that it is not worth investing in a plant suitable for the treatment of a small group of materials which are sound in their natural state and only need surface enhancement. On the other hand, we understand that the idea of a non-stop production cycle including resin coating and polishing attracts companies who work large quantities of compact stone; and accordingly we strive to design increasingly flexible Resin Lines that allow using any resin or sealer, treating all types of stone and can be programmed to work together with honing and polishing machines.