An Assessment and Evaluation of Acidic Cleaning Methods on Unglazed Terracotta Using Accelerated Weathering Test Protocols

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Theses (Historic Preservation)
terra cotta
Architectural Engineering
Architectural Technology
Historic Preservation and Conservation
Materials Chemistry
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Matteini, Irene

According to the published literature, there has been very little quantitative evaluation of the short or long-term effects of cleaning terra cotta, other than visual assessment where success is pronounced by the degree of soiling removed. Very little work (only 3% of our literature review) has attempted to measure the effects on terra cotta of various cleaning methods. Nevertheless, today, still 80% of terracotta cleaning relies on chemical products, the majority acid-based. This research evaluates the effects of acidic cleaners on unglazed terracotta to verify the potential for damage by accelerated weathering testing. This investigation continues previous studies (Matero et. al. 1996) where findings showed that by using hydrofluoric acid-based commercial cleaning system, an increased porosity of unglazed terra cotta resulted. The questions remains whether this physical alteration will lead to accelerated weathering and material damage. In the first phase of this research a Literature Review of past and current cleaning of terra cotta was completed, together with a survey of professionals involved in terra cotta restoration. In the second phase, two commercial chemical cleaners are being tested in two applications on new unglazed red and tan terracotta samples: Prosoco Heavy Duty Restoration cleaner based on HF (1:3), and Prosoco Enviro Klean based on Ammonium Bi-fluoride (generally applied as a concentrate). These are now undergoing accelerated weathering based on the Rilem salt test (V.1B) and a QUV weatherometer (ASTM G154-12) to access the effects of acid cleaning on performance. Several methods of assessment were used to evaluate the tiles before and after testing: optical microscopy, scanning electron microscopy, porosity by liquid nitrogen immersion, color change, and texture mapping imaging. By examining physical changes and their response to accelerated weathering across two typical terra cotta clay bodies, it is hoped that better cleaning methods will be considered in practice and parameters to measure potential damage as well as cleaning efficacy become established.

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<p>Suggested Citation:</p> <p>Matteini, Irene (2014). <em>An Assessment and Evaluation of Acidic Cleaning Methods on Unglazed Terracotta Using Accelerated Weathering Test Protocols</em>. (Masters Thesis). University of Pennsylvania, Philadelphia, PA.</p>
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