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20 June 2011

Thursday 16th June 2011; Diagnosis & Treatment of Granite and Bioremediation

Week 10 of 12 
Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation

This morning Jose Delgado Rodrigues, Geologist and Conservation Scientist at Laboratorio Nacional de Engenharia Civil, spoke to us on his specialist subject; granite. Granite is a holocrystalline material (entirely formed from crystalline minerals) and when formed is virtually non-porous. Its formation occurs deep within the earth at high temperature and under pressure. The processes by which the granite reaches the Earth's surface result in the alteration of some minerals, weathering and creation of a certain level of porosity due to the contraction or movement of crystals as they form. For this reason the majority of granite that is quarried and has been used in construction is already in a state of decay that has occurred over a geological timescale before being exposed in its use as masonry. The granite that is present in Scotland is one of the exceptions to this rule because the glaciation that occurred during the Ice Ages removed the upper surfaces of the granite outcrops exposing 'fresh' granite. For this reason, the types and issues of deterioration of granites that we face in Scotland are much less serious than are faced in countries where the stone was quarried in an already highly altered state.

Although it is generally unknown, granites do have a porosity, although this comes in the form of fissures and micro-fractures rather than rounded spaces connected by thin necks. The spaces are created by various processes including the different characteristics of the quartz and feldspar crystals which have different modes of elasticity and strength. The fractures are generally very well connected resulting in the granite having a notable permeability. More details to follow...

This afternoon we were rejoined by Ornella Salvadori (see Monday 23rd May 2011; Microbiological Deterioration) who spoke to us on the subjects 'Control & Prevention of Biological Growth', 'Methods of Evaluating Biocides' and 'Bioremediation'. Ornella has recommended us the book; Charola, McNamara & Koestler, 2011. 'Biocolonization of Stone: Control and Preventative Methods' (free PDF download available by clicking here). Lecture details to follow...

1 comment:

  1. That's why I hate it when people say talk here about the 'porous system' of granites... it is a fissural system! Not pores, but fissures!