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.”