The stains in the natural stone

The marked accidental of the natural stone is a frequent subject in diversity of constructive uses (countertops, pavings of hospitals, bathrooms,etc...) And on him, the Technological Centre of the Granite has proposed  investigate in these last years.

The cleaning of the stains goes through the use of products, more or less effective  , that apply sometimes without the necessary rigour, with the frequent result of an excess of failures, no only by his fault of efficiency, but by his scarce permanence in the time.

Thus, from the CTG, have studied  different varieties of natural stone commercially very known, adding to this, the different superficial finishings that apply  to the stone, including the treatments with chemical products.

The Centre of Design of the CTG, with the end to give answer to this technical need, has designed and manufactured a machine according to the specifications and prescriptions of the European norm: "EN 16301. Methods of essay for natural stone. Determination of sensitivity to the marked accidental", that allows the repeatability and reproducibility of the essay.

Between the most stood out results of this investigation, fits to signal that it has established the Index of Global Sensitivity to the marked (Isg), whose value indicates the degree of susceptibility to the marked and allows to realise comparative between different varieties of stone, superficial finishings or time of exhibition to the agents of marked.

Besides, the study of different varieties of stone in function of his petrography, has allowed to check the relation between his sensitivity to the marked and the porous system of the rock. The varieties with lower absorption and open porosity, are the less liable to the marked, and besides present better answer in front of the cleaning of permanent stains.

Another important result of this study has been that only the carbonated rocks (limestones and marbles) can present, in addition to changes of colouring, a superficial erosion, more or less intense, in front of the exhibition of some agents like the red wine.