A comparison of the long-term performance of modern paint coatings against traditional lead-based paints applied to historic wrought iron and the impact of their deterioration on the process of corrosion to the underlying metal surface in a typical outdoor environment

Meehan, Peter 2025. A comparison of the long-term performance of modern paint coatings against traditional lead-based paints applied to historic wrought iron and the impact of their deterioration on the process of corrosion to the underlying metal surface in a typical outdoor environment. PhD Thesis, Cardiff University. Item availability restricted.

	PDF (Peter Meehan PhD Thesis) - Accepted Post-Print Version Restricted to Repository staff only until 4 June 2027 due to copyright restrictions. Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (13MB)
	PDF (Cardiff University Electronic Publication Form) - Supplemental Material Restricted to Repository staff only Download (113kB)

Abstract

The conservation of heritage architectural and industrial ironwork is mainly carried out by those working in the private sector. Treatment regimes, including the use of protective coatings, have been adopted from those used in industrial, architectural and engineering contexts. Commercial standards are used when applying these coating systems that are often at variance with current conservation practices. The decision to use these coatings are based on recommendation by other practitioners in the Sector and from anecdotal evidence about their performance. There has been no testing of representative samples to gain quantitative and qualitative data to allow for the formulation of an integrated insight into coating performance over time. This study generates empirical evidence on the long-term performance of three paint coating system types applied to naturally corroded wrought iron: traditional lead/linseed oil, modern alkyd resin, and epoxy/acrylic urethane resin. Wrought iron samples were prepared to Swedish Standard Sa2.5 (near whiter metal) or Steel Surface Preparation Standard ST3 (thorough hand clean). Glass samples were painted with each coating type to act as reference standards. Samples were placed in an outdoor environment for a period of up to five years and data collected every 12 months. A number of testing methods were used to interrogate the ongoing performance of the coatings: oxygen consumption testing, electrical impedance spectroscopy, colorimetry, gloss level, visual inspection, and pull-off testing. The data collected revealed that both the alkyd and epoxy/acrylic urethane paint systems provided a continued excellent level of corrosion protection to the underlying metal. There was no real difference in the performance of the two individual systems applied to the Sa2.5 or ST3 prepared analogues. This will give the Sector confidence when cleaning historic ironwork to a lower level so as to preserve the object’s original surface and so meet a more ethical conservation approach. The lead paint system performed poorly with significant coating deterioration after only 12 months of exposure, altering its aesthetic appearance. After 48 months it no longer provided protection to the metal surface with active corrosion evident. The testing revealed that its level of protection was low from the outset with the red lead iii primer being the only barrier to corrosive agents, the topcoat having failed prematurely. The lead paint system was probably incorrectly prepared, particularly the composition of the topcoat, and explains its deficient performance over what was expected. So, no conclusion on its performance was possible for its use as a commercial paint system. The use of an integrated testing approach to assess the performance of the three paint coating systems provided quantitative and qualitative data that allowed for an informed assessment of their ongoing performance. This will allow Sector practitioners to make informed decisions when choosing coating systems for use on historic ironwork. The research confirmed that the Sector should have no concerns over the use of correctly specified and applied modern paint systems for the protection of heritage ironwork.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > History, Archaeology and Religion
Subjects:	C Auxiliary Sciences of History > C Auxiliary sciences of history (General) Q Science > QD Chemistry
Date of First Compliant Deposit:	4 June 2026
Date of Acceptance:	2 June 2026
Last Modified:	04 Jun 2026 13:56
URI:	https://orca.cardiff.ac.uk/id/eprint/187398

Actions (repository staff only)

Edit Item