AIC's 47th Annual Meeting

Aged coating fracture (single or multiple-layer) is a frequent condition concern for sizeable historic architectural and object surfaces. The author has successfully utilized a hand-held digital force gauge, pioneered in 2001 by Winterthur Museum conservators, to assist triage decision-making in the field for compromised coatings.  This in situ testing can help evaluate whether coatings should be pre-consolidated prior to moving or handling and aid in feasibility assessment of whether consolidation and encapsulation can provide condition improvement for fragilely bonded coatings via minimally invasive quantitative evaluation. While other adhesion tests require time-consuming adhesive-dependent dolly attachment or relatively large, deep surface scoring, this method requires only temporary dislodging of an approximately 0.125-inch square coating fragment.  Recording initial average baseline measurements for coating bond via compression force required to initiate coating failure, the relative additional force required to initiate failure after consolidation treatment can then be compared to aid in performance-based consolidant material selection. Case studies in which coatings and consolidants have been evaluated in this manner by the author on substrates that include interior and exterior coating brick, wood and metal surfaces will be presented as will hypotheses for mechanisms potentially contributing to results obtained.  While recognizing that this protocol represents just one of the five loading conditions for testing bonded articles, as a low-tech method easily performed on difficult and limited access situations, it provides a basis for consolidation material selection. As with other forms of coating adhesion testing these test results do not predict coating life expectancy nor can they account for variations in substrate condition interlayer cohesion differences that may also impact the integrity of historic coatings.