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Heritage wrought iron: towards the development of evidence based standards for coating

Emmerson, Nicola 2015. Heritage wrought iron: towards the development of evidence based standards for coating. PhD Thesis, Cardiff University.
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Abstract

Effective management of heritage assets relies on decision-making which is underpinned by empirical evidence of impact of treatments on long term survival prospects of materials. Historic wrought iron presents a particular problem for conservation. It occupies a niche position between heritage and engineering, is frequently exposed to outdoor atmospheric corrosion and, in the case of bridges, gates and similar structures, may be required to perform a distinct function. Sector guidance to direct practices is based on anecdotal evidence and established methods. British Standards relate to modern steels hence application to historic ferrous metals is complicated by differences in metallurgy and lack of concession to conservation ethics. This study generates empirical evidence of the effects of five surface preparation methods and three protective coating systems on the corrosion rate of historic wrought iron samples. Immersion in sodium hydroxide solution and blasting with crushed walnut shells are found to reduce corrosion rates of uncoated wrought iron. Aluminium oxide and glass beads blasting increase corrosion rate but offer removal of contaminants and a keyed surface for coating adhesion. Flame cleaning increases corrosion rate by almost four times the uncleaned wrought iron corrosion rate. A two-pack epoxy resin coating system with polyurethane topcoat applied over substrate surfaces blasted to Sa2.5 (near white metal) and a surface tolerant single-pack alkyd coating applied over coherent oxide layers successfully prevented corrosion for almost two years in high static relative humidity environments. An alkyd system applied over Sa2.5 blasted surface does not significantly reduce corrosion rate of the uncoated substrate. A cost benefit approach to interpreting the empirical results in relation to practicalities of applying the treatments is advocated. The methods developed for standardising historic sample material and measuring oxygen consumption of coated samples as proxy corrosion rate offer scope for further work in this area. A standardised approach to testing permits correlation of test data between workers in this area to generate a database of empirical data to inform decision-making.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: History, Archaeology and Religion
Subjects: C Auxiliary Sciences of History > C Auxiliary sciences of history (General)
Date of First Compliant Deposit: 30 March 2016
Last Modified: 13 Jan 2018 02:30
URI: http://orca-mwe.cf.ac.uk/id/eprint/84439

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