Conservation Solutions, Inc: Art + Architecture + Artifacts

Terra Cotta Cleaning Tests for Bank of Montreal Building

Site
Bank of Montreal, 2 Queen St. E., Toronto, ON, Canada
Client
Brookfield Office Properties Management LP

Conservation Solutions, Inc. (CSI) was contracted to perform cleaning tests on the terra cotta façade of the Bank of Montreal Building at 2 Queen Street, Toronto, Ontario, CA.  A black stain had been noted on the façade that the client wished to have removed. The goal of the testing was to identify the source of the stain, characterize it, and develop treatment recommendations for its removal.

First, the stains were tested using a portable X-ray Fluorescence Spectrometer (XRF).  Readings indicated that the stains showed a high percentage of manganese, a mineral often found in terra cotta clays and one that can mobilize and become soluble in acidic solutions, migrate to the point of evaporation, and be deposited at the surface, as was observed on the Bank of Montreal Building’s terra cotta façade. The readings also showed a higher percentage at the sites of highest stain concentration while reducing in percentage at sites with lesser or no stains, thus confirming the association of the stain with manganese.  

Chemical and biocide cleaners were tested, in addition to laser ablation.  Care was taken to prepare all surfaces prior to testing, to document all stages of testing, and to protect surrounding areas on the terra cotta that were not to be cleaned.  Recommendations for treatment based upon the testing results were provided to the client, along with all testing documentation.