One of the most common disputes investigated by CERAM subsidiary, CSMA involves coating problems on buildings. The stakes here are high as the cost of recovering buildings can run to several £million. Surface and interface analysis techniques are crucial to probe into the paint and determine the history as it was laid down. CSMA has several expert witnesses, one of which specialises in this kind of investigation.

A leisure complex was under construction when a serious delamination of paint was observed on the steel structure. The paint was of an intumescent type i.e. fireproof, this requirement is driven by legislation. Large areas of paint were spalling off and the most severe had already undergone remedial action.

The objective of this exercise was to determine a failure mode for the paint.

Methodology & Results

During a site visit, samples of paint were carefully harvested for analysis. XPS (X-ray Photoelectron Spectroscopy) techniques were used, which provide quantified elemental and chemical state information from failure interfaces, and ToFSIMS (Time of Flight Secondary Ion Mass Spectrometry) which provide detailed molecular information from failure interfaces.

The XPS and ToFSIMS results showed that there was no unusual chemistry evident in the failed samples and that no obvious contamination had been introduced between the primer and the intumescent paint binder.

SEM (Scanning Electron Microscopy) techniques were also used which showed that the intumescent paint topography followed that of the primer topography (i.e. where the primer was smooth and shiny, the overcoat also appeared smooth and shiny).

Analysis of the remedial work area strongly suggests that a mild abrasion of the primer surface (“roughening up”) helps provide a better physical and/or chemical key for the overcoat.

Conclusion

It is most likely that the lack of an adequate chemical bond on the original smooth primer surface was the main cause of delamination.