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Pitting ranks among the very frequently arising damage forms of Werksteinen, in-special such from historical (thus old) buildings. Easily weatherable and acid-sensitive materials and components, for example from limestone or marble, are of it frequently concerned. The development of pit and/or the Pitting can have different causes. One can attribute the Pitting to two possible causes:
The "Pitting" ranks among the very frequently arising biogenous damages at lime and marble components. Pit are predominantly noticeable by their (above all microscopic) multiplicity, do not rank however not among those kinds of damage, which cause a very strong damage. Individual pit if the certain size and quantity exceed, then they are with the naked eye visible and lead first to an aesthetic impairment, later, with increasing damage, also to a threat of the built volumes.
Can be differentiated, depending upon size of the individual pits, macro pit and micro pit. All that, by which naked eye visible damages become, as macro pit designation and of those distinctive, which are recognizable under the microscope only, micro pit. In "Pitting" damaged stones exhibit round to oval defect places with concave a concavities of different depth. These rich education large in their dimensions of microscopic orders of magnitude up to individual 1.5 cm.
While "macro pit" quite selectively into action go, the "Mikropitting" is very many further common.
Micro pit can be attributed to settling the rock surfaces by Dematiaceen and epi and endolithische lichens. The damage of the stone effected via these lichens and mushrooms via combined chemico-physical-mechanical Verwitterung.Die main cause of the damage and the development of pit lies in the Stoffwechselprodukten of the mentioned micro organisms justified. Among the most important connections which can be called here rank carbon dioxide (CO_2), citric acid (C_6H_8O_7) and oxalic acid (C_2H_2O_4). With the solution of these connections in water it comes to the release of Oxoniumionen and thus to a sinking of the pH value. The release of these decomposition-active Stoffwechselprodukte leads in the direct surrounding field of these organisms to a chemical decomposition of the marble. For corroding and/or solution processes with the emergence of the "pits" walls, which form concentrically around the lichen located in the center, speak their smooth and round.
The damaging organisms do not however only occur at the surface of the stone. If it permits the porosity of the stone, lichens leave themselves even in deeper regions, below which, prove surface of the stone. This is however possible only if the marble offers place by a sufficient large pore area sufficiently for a settling. So can for example by the inter+granular destabilization and by microcracks sufficient place for a settling offer.
A condition for a successful massive settlement of a marble by mushrooms and lichens is a marble weakened in its firmness as well as the sufficient supply of water and light. Here the anthropogen worked on surfaces offer an ideal condition e.g. from marble. By the treatment with tools a destruction and/or an attenuation of the grain structure (e.g. of marble) takes place. Here ideal points of attack are offered for the penetration of the Myzels of lichens and mushrooms. Individual colonies settle the surface and continue to penetrate in pore areas and intergranular gaps. With metabolic reactions and mechanical pressure of this biomass it comes to an additional loosening of the connection of the Kalzitkristalle concerned. With progressive damage also individual (Kalzit) Kristalle.Die of "macro pit" separates comes out by gradual growth directly from the microscopic forms of the Pittings. As an active damage cause for macro pit can almost exclusively mushrooms for the group of the Dematiaceae (yeast-like mushrooms) belong to apply. They form black, knotige micro colonies.
That purely chemically/physical Pitting can be attributed to corrosion processes of different kind. As a possible example inclusions of pyrite in the marble are to be called. The pyrite can be subject to oxidation processes with the contact with atmospheric oxygen and humidity, which entail again the education of sulfuric acid as one of the oxidation products. The sulfuric acid is neutralized by the surrounding Kalzit, leads however by the neutralization reaction to its dissolution. Micro and macro pit around the former, later completely weathered, to pyrite inclusion are the result.
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