In spite of heavy investments in modern production lines and good quality resin, many stone processors are still dealing with the incomplete filling of defects. Thin cracks running deep into the thicknesses, holes and crevices remaining on the surface polished to a mirror finish, and large full-thickness pits are the most common problems. Let’s examine causes and consequences of each of these cases in detail.
It is a fact that seemingly sturdy slabs can contain fine narrow cracks that have not been completely saturated with resin and hence have not been stabilized. These are almost always naturally-occurring fissures which have split, and the stone fabricators know very well that they should be regarded as “active cracks” with the potential to undermine the integrity of the slabs, and namely cause the material to chip or break during the manufacture of fireplaces, vanities, tables, kitchen countertops, stairs, windowsills, skirtings, wall panels and so on. There are several factors which can hinder the resin penetration into the finest cracks:
1) The slabs are not honed prior to being resin coated.
2) The technique of stone drying is ineffective.
3) The surface of the slabs is not been meticulously swept using an appropriate brush.
4) The resin product is too thick.
5) The resin product sets too quickly.
6) The cure temperature is too high.
It is noteworthy to mention that most often the incomplete filling of thin and deep cracks is caused by a combination of factors (especially the points 4, 5 and 6) occurring simultaneously.
Notwithstanding that the blocks extracted from a certain quarry feature an optimum grain size and wonderful colours, the slabs machined down from them will never be sold at full market price if there are holes and crevices on the polished surfaces. There are a number of potential reasons and combinations of reasons why slab producers may find it difficult to block up cavities which are deeper than 3 or 4 mm:
1) Workers do not apply sufficient amounts of resin to the slabs.
2) Workers do not apply the resin carefully enough.
3) Workers miss to carry out the “retouch”.
4) Workers do the retouch carelessly or wrongly.
5) Workers should carry out various retouches.
6) The time separating the initial resin coating from the final retouch is too short.
7) The resin product is too runny.
8) The voids should be filled with mixtures of high viscosity resin and stone crushed into chips and powders.
9) Surface filling should comprise of two resin treatments interrupted by honing.
Unfortunately, it has become common practice among inexperienced stone processors to fill holes and cracks with coloured “epoxy gels”. Anybody would find it easy to block up holes with gel products indeed; and yet the gel fillings are rather awful-looking and not really long lasting. The point is that the epoxy gels were never devised for surface restoration and enhancement (as we explained in our previous editorial titled “Important aspects of the repair and restoration of marble which are often overlooked and underestimated”).
Owners of “coloured” or “breccia” marble and onyx quarries interested in cutting their blocks on an industrial scale have been long asking themselves what to do with the slabs that have huge full thickness pits. We must in all honesty say that it is impossible to learn the proper methods for restoration of fragile stone without a teacher. For example, only a few experts know how to fill and repair onyx slabs with “patches” made of resin and pieces of stone that can hardly be distinguished from natural waving at first sight. To seal cracks which go all the way through the slabs and though are not so wide it is enough to follow the instructions provided in the afore mentioned article: “Stone processors needing to treat marble damaged with fractures and holes which are so deep to pass through the entire thickness of the slabs, should always block the cavities up before the material is loaded on the plant, to ensure they are thoroughly filled with the resin that is applied to attach the fibreglass mesh. The resin would otherwise seep through the cracks without filling them indeed, and as a consequence the desired strengthening would never take place. In summary, dedicated stone processors should close the major faults of the slabs on the side of surface – the one which will be then resin coated and polished – to make sure that the voids are saturated with resin at the time of mesh backing. Factory workers can seal holes and fractures with either quick setting mastic or adhesive tape, or even both these products, depending on the amount, extent and depth of cracking and holing. Regardless of which product workers choose, the operation has to be carried out with the slabs held vertically by a robot loader or a clamp connected to the hoist of a jib crane”.
Over the course of the years, Commerciale Graniti established a pre-eminent reputation as a trustable partner to whom traders and brokers dealing in rare and expensive stone entrust their material to have it turned into slabs suitable to meet the strictest standards for strength and quality of surface finish.
Working with the world’s finest marble and granite on behalf of export-oriented companies focusing towards developed markets requires to demonstrate high levels of involvement and to assume significant responsibilities. The factory staff has a thorough grounding in all aspects of slab manufacturing process indeed; and moreover they run a modern machinery park that comprises of the most technically advanced production lines, including a resin plant from the “Res Combi” series tailored to carry out some peculiar treatments, like the darkening of black granite coming up with white stains or white ring marks.
Recently, Commerciale Graniti has launched an efficiency and productivity improvement plan; and as a first step, its management commissioned S.E.I. to design a Resin Line which would make it possible to adapt the mesh backing and resin coating techniques to the characteristics of every kind of stone.
Even in the eyes of visitors who are not really machinery experts the revolutionary Resin Line opened a few months ago looks so impressive to evoke the image of a gigantic automated laboratory complex. In fact, the method of working of conventional resin plants (which involves the slabs passing through a rigidly predetermined sequence of workstations) has been rethought and rather widened through the inclusion of a number of “multipurpose workstations” capable of performing several functions according to material.
There are so many properties and aesthetic features (structure, thermal resistance, amount and severity of cracking and holing, background colour and veining to name but a few) which may vary from one type of stone to another in truth; and to achieve the best results on a consistent basis is possible only if the processing route for slab production across the resin plant varies correspondingly. For example, in spite of having the same origin the marble varieties extracted from the Apuan Alps can differ in their water absorption rate, hardness, types of faults and hue; and hence require specialized treatments.
That being so, the slabs of highly porous marble invariably rest in both the drying units of the new Resin Line (consisting of tunnel and multi-shelf ovens), while the slabs of low water absorption marble simply pass through the tunnel oven. The mesh attachment and resin coating area of the plant is composed of two workstations within 8 metres of each other, so that the operators can locate cracks which remain open after the initial resin application and do as many retouches as they need to ensure the thorough filling of fractures, pits and voids. The time and temperature for resin curing are always in strict accordance with the producer’s instructions thanks to the innovative design of the polymerization unit that results from the combination of two multi-shelf ovens programmed to work together or separately, depending on the setting speed of the resin.
Stone companies starting to resin treat their marble slabs on a large scale will almost invariably receive lots of advices and instructions from agents and area managers seeking to sell them machinery, tools and consumables. Yet, most these consultants have never had anything close to a practical first-hand experience of restoration and enhancement of stone, having just learnt some basic rudiments through watching real professionals at work.
That being so, it often happens that people who are unfamiliar with resin treatment of marble try to teach novices. The students of such “self-promoted instructors” may then believe to have reached fairly high levels of dexterity, and hence decide to hire apprentices and personally train them. This state of things establishes a vicious circle, as it interferes with the process by which knowledge and skills are transmitted from teachers to students, so that within a few generations of practitioners the resin treatment’s repertoire of techniques and methods inexorably narrows. If we look at what the resin treatment is in actual fact – a wide and complex system – we can easily deduce that anyone – anyone, however intelligent and keen – who is taught an incomplete version of the methodology, will never obtain satisfactory results in terms of repair and reinforcement of faulty marble. In this regard, it is worth mentioning a part of the resin treatment system which is far too often underestimated or, worse, completely ignored: the proper preparation of marble slabs before they are loaded on the Resin Line.
Stone processors needing to treat marble damaged with fractures and holes which are so deep to pass through the entire thickness of the slabs, should always block the cavities up before the material is loaded on the plant, to ensure they are thoroughly filled with the resin that is applied to attach the fibreglass mesh. The resin would otherwise seep through the cracks without filling them indeed, and as a consequence the desired strengthening would never take place.
In summary, dedicated stone processors should close the major faults of the slabs on the side of surface – the one which will be then resin coated and polished – to make sure that the voids are saturated with resin at the time of mesh backing. Factory workers can seal holes and fractures with either quick setting mastic or adhesive tape, or even both these products, depending on the amount, extent and depth of cracking and holing. Regardless of which product workers choose, the operation has to be carried out with the slabs held vertically by a robot loader or a clamp connected to the hoist of a jib crane.
A good quality semi solid mastic – suitable to be applied to wet surfaces with trowel or spatula, compatible with the epoxy resin likely to be used for coating the slabs, and coloured to match the hue of the material – is an excellent means to close large holes. Nonetheless, there are cases where the presence of mastic on the mirror polished slabs looks far too showy or even unsightly, for example, if the material has uniform pale colour and background, like cream, beige and white marble varieties. The best way to overcome this drawback is to partially grind the mastic fillings and replace them with mixtures of liquid epoxy resin, oxide pigments and crushed marble.
A waterproof adhesive tape that withstands high temperatures is ideal to seal long hairline cracks, including those which run diagonally. To remove the adhesive strips before resin coating the slabs is not difficult at all; notwithstanding, this job requires attention to detail and accuracy to ensure no residue of tape is left on the marble surface.
Brazil boasts an abundance of mineral wealth including immense deposits of fine building and decorative stone derived from bedrock sources. This great quantity of fine stone has surely represented the most significant factor behind the tremendous growth in the Brazilian stone industry. However, Brazilian stone processors should be credited for growth of their field too, as most of them show both entrepreneurial flair and a passion for doing business, with a policy of continuous investment in mechanization, modernization and expansion of their manufacturing facilities.
Decolores Mármores e Granitos is a perfect example of companies forever striving to meet the international strictest quality standards and even exceed customer expectations through a combination of latest machinery and qualified experienced staff. Over the years, its team has developed so many specialized processing methods and techniques that today they are able to turn all types of Brazilian stone into highest quality slabs, even when it comes to working with varieties widely regarded as far too problematic because of extensive fracturing or unusual colouration, such as fragile faulty “exotic” granite and white diaphanous quartz.
In the light of the fact that much material has to undergo complex treatments involving the use of synthetic resin, Decolores’ management made a decision to set up a technologically advanced restoration, reinforcement and enhancement unit consisting of two automated production lines.
The high mechanical speed of the first resin plant makes it possible to achieve very high outputs, especially in the case of relatively sound granite which only needs a uniform resin coating so as to fill any micro fissures or tiny pinholes whose presence on the mirror-polished surfaces would cause a loss in value of the slabs.
The second Resin Line is primarily intended to strengthen the structure and improve the appearance of exotic granite, quartzite and quartz. Given the high absorption rate of various kinds of Brazilian stone, this plant is equipped with an oversized drying oven where the slabs rest for no less than 80 minutes at a temperature to be set according to the chemical properties of each material. The area where a layer of fibreglass mesh is stuck to the back of fragile slabs and the stone surface is resin coated, contains a series of worktables for manual repair operations, and an exceptionally complete equipment composed of a curing oven for fast-setting resin, a vacuum chamber – that makes a big difference to the quality of the finished product ensuring the thorough filling of hairline fractures – and a stacker aimed to extend the time separating the initial resin application from the finishing touch which comes in handy whenever the stone is pitted and holed.
The main curing oven is remarkably large if compared to the productive capacity of the plant in order to allow the slabs resting in the polymerization chamber for a far longer than the average period. As a result of this, the company can consistently use slow setting epoxy systems, such as the resins developed for intensifying the colour of dark green, blue, brown and black granite, and the non-yellowing products suitable to treat translucent quartz and – more generally – light-coloured material.
Anyone who has some familiarity with stone restoration knows the difference between materials which need to be treated on both sides, that means mesh backed first and then resin coated, and those which only need to be resin coated.
In most people’s opinion fractured slabs should be reinforced with fibreglass, while mesh backing stone with no visible cracking seems pointless. This classification is only partially correct, as the issue of reinforcement is far too complex to be reduced to the two equations: ‘presence of large cracks = mesh backing is necessary’ and ‘absence of large cracks = mesh backing is unnecessary’.
There certainly are materials which are so sound in their natural state that they do not need any reinforcement, and this is the case of much granite. However, in order to avoid big mistakes it is worth clarifying the exact meaning of the adjective “sound”.
In fact, so many machinery makers misinterpret the significance of mesh backing and even worse diffuse misconceptions among slab producers. If you take a look to various catalogues, blogs and websites, you will find explanations according to which “mesh reinforcement is required when it comes to the treatment of slabs that present numerous cracks”. Whoever writes this undervalues or simply doesn’t know a crucial point: the absence of huge cracks does not in itself mean that the slabs are sturdy. Therefore, it is absolutely wrong to believe that stone free from extensive fractures and large irregular voids should not be mesh backed, because there are a number of varieties of marble and limestone – as well as some types of granite – that have hairline cracks which although fine and narrow can weaken the slabs and eventually be the cause of their breakage.
Obviously, hairline cracks’ worsening takes time, and yet this is not a good reason to neglect to carry out a proper reinforcement. In fact, once polished the slabs have to be moved to specialized workshops, where they are transformed into made-to-measure stone coverings, pavings, bathrooms, kitchens, tables, fireplaces, to name but a few. In the vast majority of cases, this means that the slabs have to be bundled, loaded into trailers or containers, transported over great distances (the transport can take weeks), unloaded and unpacked. Besides, small and medium scale companies source slabs from large importers and dealers, and accordingly have to collect their stone from warehouses, and transport the material using A-frame supports secured to the bed of a truck with the slabs tightly strapped and fastened to the support frame.
The production of made to measure items involves a repeated number of handling operations too, as the slabs are moved from the store and loaded on the worktables of bridge saws, contouring machines or waterjet cutting machines.
In summary, the polished slabs are subject to mechanical stress that may cause a small fault to turn into a huge crack; and hence to strengthen stone tending to break is a necessity. To whoever raises objections this leads to increased production costs, we reply that spending a few Dollars more per square metre is far preferable to bearing huge financial losses due to breakage of slabs.
Notwithstanding the above, we do not purport that slabs with hairline cracks or micro fissures should be always and in all cases mesh backed. For example, tiny fractures are not a problem for stone processors operating factories where the slabs are polished and nearly immediately cut to size. As well, companies dealing in cheap stone are simply forced to keep production costs down, and thus they are right not to reinforce relatively sound slabs.
The decision on whether or not to carry out a mesh backing should be also based on the intended use of the slabs. Indeed, there are situations where the use of mesh backed stone is advisable and cases when fibreglass looks unsightly or hampers the work of stone installers and tilers. In this regard, it is noteworthy to mention that fitting teams often complain about the incompatibility between the resin/fibreglass reinforcement and adhesives for the installation of natural stone. However, this is not a major obstacle because real experts in marble fitting know various methods to bypass it.
Other factors to be taken into account are thickness and dimensions of the slabs to be processed. Needless to say, 2 cm-thick long narrow slabs (e.g. 320 cm X 100 cm) will break much more easily than compact-sized (e.g. 220 cm X 160 cm) 3 cm-thick slabs.
Spain abounds with marble deposits that produce some of the world’s most sought after varieties. Professional stone distributors will never miss to include Crema Marfil, Marron Emperador and Rojo Alicante in their product range indeed, and most of them will also offer other Spanish materials which are much in demand all over the world, like Nero Marquina, Crema Valencia, Grigio Cheghin, Rojo Coralito and Amarillo Triana to name but a few.
Alicante province has always been one of the major slab and tile producing areas, as a number of leading stone processors are located there. Palazon y Mira SL is a long-established company forever striving to improve the quality of its production systems through the introduction of new technologies. This combination of practical experience and adoption of advanced machinery allows Palazon y Mira turning severely cracked blocks into top quality slabs and achieve surprisingly high levels of productivity.
Recently, Palazon y Mira took a significant step towards upgrade of its factory. The company owners carried out an extensive research to ascertain what processing plants for marble reinforcement and finishing are the most efficient and reliable, and eventually came to the conclusion that the S.E.I. Resin Lines represent the best solution for the restoration and enhancement of Spanish marble. Therefore, they chose a Resin Line tailored to meet their requirements – the “Res 105 Lux CS” type – whose salient design feature is the impressive mechanical speed that ensures the maintenance of high production rates over the 24 hour workday. This stunning mechanical speed results from the peculiar design of the automatic loading and unloading workstations – that avoids production slowdown even in the case of slabs which present numerous fractures – and the fact that the various machines which form the Resin Line are arranged logically and programmed to coordinate in a rational structured manner. The record-large curing oven is compatible with all polyester and epoxy resins for stone treatment available on the market today, irrespective of their viscosity and reactivity.
In the past few years almost all the machinery makers who produce resin treatment plants have learnt to include one or two tables to allow stone processors carrying out the so-called “retouch”, which is the application of a second or even third layer of resin onto the surface of faulty slabs. Some of them have also begun to persistently offer stackers (otherwise called “accumulators”) aimed to stack 5 to 10 slabs between two tables so as to extend the time separating the initial resin coating from successive retouch.
Although everyone agrees resin application should be repeated, slab producers often receive imprecise, or worse, wrong explanations of the reasons why the retouch is necessary and instructions on how to do it. Indeed, so many machinery dealers with no direct experience in the field of stone repair and little understanding of resin treatment try to attract customers by pretending to be experts.
Let’s try to make things clear and offer some good food for thought for all who are planning to invest in a resin plant. Unquestionably, in the vast majority of cases resin should be applied no less than twice. However, there are occasions where one coating may be enough to achieve the desired results (e.g. surface enhancement and sealing of naturally sound stone).
It is very important to understand that retouches are necessary not only to repair surface cracks but also to attach the fibreglass mesh correctly. Indeed, after laying a sheet of reinforcing mesh onto the back of the slabs workers should always locate fractures which remain open under the fibreglass, and pour further resin to thoroughly fill them. Even more important is acceptance of the fact that it is impossible to predict or decide a priori how long workers should wait before starting to retouch the initial resin coating, and how many retouches should be done. It all depends on the conditions, chemical properties and colour characteristics of the stone. Indeed, on the market there are hundreds of types of resins, and to choose the right product for the treatment of a specific stone, dedicated slab producers should take into consideration the characteristics of their material, and namely its chemical properties and aesthetic features (colour, pattern and veining), and the nature of its faults. The viscosity, penetration capacity and reactivity (gel time) vary from one resin to another, and the method for application should vary with them.
In this regard, it is worth mentioning one of the tips that has been provided in our previous editorial titled ‘Choice criteria in the selection of resin plants’:
“First of all, you should have clear ideas of what the most frequently treated materials will be. In fact, the extent and equipment of the “mesh attachment and resin application station” (number of worktables, possible inclusion of vacuum chambers, stackers, mesh dispensers and resin applicators) have to be decided according to the conditions of the slabs, that is to say likely quantity and nature of cracks.”
It is surprising to see how quick Tümas Marble has grown in the past few years. This unstoppable growth is definitely due to the constant availability of large quantities of blocks, which can be transformed into slabs of varying thicknesses, tiles and even made-to-measure stone products. Indeed, the company owns a number of quarries, which produce a range of increasingly fashionable stone, such as an elegant marble with a soft cream and light beige palette named “Crema Colossae”.
Another key factor for success is the ambitious equipment modernisation plan. Tümas managers are aware that companies wanting to rise and assume a leading position in a steadily more competitive market should offer best quality products, which is only feasible through the use of state-of-the-art machinery. This is why they are incessantly looking for the latest and most efficient machines to improve the efficiency and productivity of their Denizli-based factory. And so it was that in 2011 they chose one of the most effective existing technologies for structural reinforcement and surface enhancement of marble (especially “coloured” and beige materials), limestone and onyx: the “Res 60 Combi XT” Resin Line. The slabs treated with this plant were of such a high standard that customers began to place growingly larger orders, so that in just one year the sales almost tripled and the productivity of the Resin Line became insufficient to meet demand. In that time, the board management made the decision to expand the plant and turn it into a far bigger model: the “Res 90 Top CS” type. Though the expansion made it possible to work twice as fast as with the “Res 60 Combi XT” Resin Line, it did not take long before the sales again exceeded the productive capacity. And so to the final the company’s directors resolved to build a brand-new shed where to install a gigantic “Res 200 TriLux” type. The layout configuration of this model is the fruit of an-depth study aimed to design an automated production line to carry out the entire process and ensure high levels of productivity even in case of severely cracked stone.
The loading workstation consists of a rotating platform to store 120 raw slabs and an automatic loader able to pick up irregularly shaped slabs with deep fractures, and place them on sturdy “close-mesh” conveyor trays. A 50-slab capacity multi-shelf oven provides thorough drying of the slabs which then pass to the mesh attachment workstation, where a sheet of fibreglass mesh is glued to their back through the application of epoxy resin that eventually hardens in a 75-slab capacity multi-shelf curing oven. The mesh reinforced slabs are overturned by the high-speed “LL ROB” robotic system that also transfers them to the resin coating workstation. To allow factory’s workers ensuring that all faults are completely filled with resin a series of resin application tables is included. Besides, the slabs are impregnated under-vacuum, carefully checked and retouched. The resin coatings harden in another 75-slab capacity multi-shelf oven. On leaving the curing oven the mesh backed and resin treated slabs move to the unloading workstation, where they are automatically unloaded and stored next to the plant.
Today, there are so many resin plants for slabs on the market that stone processors may find it hard to choose the ideal one. Indeed, with such a vast array of models and brands now available it is easy to get confused and make wrong decisions.
Slab producers should be aware that the use of inappropriate plants for the restoration of faulty stone may blunt their competitive edge. Indeed, companies who choose resin plants which are not suitable for their production requirements will never be able to meet the quality standards demanded by developed countries, and accordingly they will lose significant market share to their main competitors.
For example, companies dealing in onyx who pick plants equipped with curing ovens which are small if compared to the work rate will soon regret their investment, because they will be forever counting the damage done by the high temperatures set by their ovens’ manufacturer to speed up the cure greatly.
Here are a few handy tips from us to ensure you choose the right make and model to suit your individual needs.
First of all, you should have clear ideas of what the most frequently treated materials will be. In fact, the type of loader (manual, semiautomatic or automatic) and the extent and equipment of the “mesh attachment and resin application station” (number of worktables, possible inclusion of vacuum chambers, stackers, mesh dispensers and resin applicators) have to be decided according to the conditions of the slabs, that is to say likely quantity and nature of cracks.
The right type and capacity of the drying and curing ovens depend on the chemical composition of the stone, and exactly on its water absorption rate and thermal resistance.
The resin properties must be in line with the colour of the material. For example, white marble slabs must be coated with non-yellowing slow-setting resins. Therefore, the size and heating system of the curing oven have to be compatible with the resin used extensively by the factory’s workers.
You should carefully calculate how many slabs you expect to process in a day, and make sure that the mechanical speed of your plant (which results from its layout configuration and level of automation) will be high enough to allow you achieving your production target on a continuous basis.
At that point, you should decide where to position the plant in your factory. If two or more areas are available, then you should choose the one which is ideal to speed and streamline the slab production process, and so it is essential to plan the interaction with existing or planned pieces of processing equipment, such as gang saws, honing and polishing lines. In the case of constraints due to the shortage of space, the machinery designers will have to prove their creative skills and tailor design a plant that fits in the site and boasts all the necessary features.
Expert staff and advanced equipment enable MLP & C s.r.l. to cover all the aspects of the slab production process; and accordingly to provide a comprehensive range of sub contract processing services including block dressing and cutting, slab mesh backing, restoration and follow-up honing of severely cracked slabs, surface resin coating and “fine-honing” or “mirror polishing” surface finishes.
At the company’s Castelnuovo Magra-based factory, a few kilometres away from Carrara, no block will be ever found “too problematic” and returned to a customer because of extensive fracturing. Indeed, all defective blocks are thoroughly examined to see type and nature of their faults, and then subject to a special reinforcing treatment which eliminates the risk of gang saws smashing the blocks due to the great pressure of the diamond blades.
It is noteworthy to mention that MLP was one of the first companies in the world to have a Resin Line: an S.E.I.’s 1st generation model installed at the beginning of the ‘90s. This plant has been continually running until a few months ago, when a 6th generation “Res Combi Max” Resin Line took its place.
The new Resin Line is equipped with an automatic loading and unloading workstation consisting of two “VK ROB” robots and as many “RP” rotating platforms. The robots are capable of “book matching” the raw slabs and turning over the mesh backed ones (to have their surface resin coated without breaks). Furthermore, they are programmed to allow workers sealing the cracks which are so deep to pass through the entire thickness of the slabs before a mesh backing is carried out, and to hand grind the back of the processed material. The remarkably high carrying capacity of the rotating platforms (120 slabs) prevents a slow down through insufficient slabs in the loading area and avoid congestions in the unloading area.
The loading robot puts the slabs onto sturdy “conveyor trays” with close-mesh tops, which are an ideal means of transport for broken, tiny and irregularly shaped slabs; that is one of the reasons why MLP can repair and strengthen onyx, breccia and “coloured” marble slabs on an industrial scale.
The slabs are left in the drying oven for no less than 100 minutes and exposed to an intense flow or warm air. As a result, the level of residual humidity of the stone is so low that it cannot affect at all the cure of the resin. Indeed, success largely depends on proper resin polymerization. Epoxy resins should always harden according to the time and temperature specified by resin makers and used in accordance with their intended purpose. The most common mistakes are trying to accelerate cure increasing the amount of hardener or exposing the slabs to extreme heat. Generally, when it comes to the restoration and surface enhancement of valuable stone, the most appropriate chemical products are low viscosity and slow to ultra-slow curing epoxy resins, and accordingly the polymerization oven of MLP’s Resin Line is roomy enough to ensure pretty long storage times ranging from 160 to 240 minutes.