I truly enjoy articles written by Dwight Weldon, Richard Burgess and earlier Clive Hare.
I write to expand on the above mentioned article for purpose of highlighting the very notable performance differences between the CSA (Calcium Sulfonate Modified Alkyd) coating referred to in their Nov. 2015 article and the HRCSA (High Ratio Calcium Sulfonate Alkyd) coating featured in JPCL: August 2009, page 18 article: “Overcoating Lead-Based Alkyd Paint on Steel Penstocks: Practical Experience” which many perceive to be one and the same – which they are not.
I was both relieved and satisfied to see that Dwight Weldon’s November 2015 article had correctly assessed that the multi-coat CSA (Calcium Sulfonate Modified Alkyd) inter coat separation problem was due to the coating formulation from a specific manufacturer, and by no means was the fault of the contractor.
The single coat HRCSA (High Ratio Calcium Sulfonate Alkyd) formulation offers not only a 25 year field history of reliable recoat and overcoat performance, but most notably the unique ability to chemically stop structure critical corrosion, pack-rusted corrosion cells (rust bleeding)and ability to free up corrosion-frozen bearings a feature neither supported by CSA or other coating systems.
To further authenticate that HRCSA single coat system does not separate between coats like the aforementioned CSA coating did is that the HRCSA is a one coat system and not a multiple coat system. Additionally, recent inspections of the penstock project described in JPCL 2009 Overcoating article revealed less than 1 sq. meter total accumulated corrosion on the structure’s 50,000 square meter coated surface including crevice corroded areas further validating HRCSA’s ability to chemically neutralize active corrosion over the long term. Additionally, HRCSA Performance characteristics have been confirmed from both lab testing and field trials as revealed in Publication # FHWA-HRT-11-046 ”Performance Evaluation of One-Coat System for New Steel Bridges” as well as on hundreds of HRCSA corrosion mitigated bridges and structures across North America and around the world.
Thanks to the JPCL: August 2009, page 18 article: “Overcoating Lead-Based Alkyd Paint on Steel Penstocks: Practical Experience”, Preservation Engineers and project managers/planners are empowered to correctly specify HRCSA coating based on defined characteristics from page 24 (with the Ratio of Active Sulfonate to the Total Base Number being between 90 and 105 TBN and a minimum 9.5 to 11% Active Sulfonate as determined by titration testing). Doing so ensures that owners and engineers who specify the HRCSA rust mitigation coating system and not the CSA coating system will receive the same verifiable physical and chemical properties that ensure the HRCSA high performance, field tested single coat corrosion mitigation system and added ability to chemically stop structure critical corrosion on our nations bridges.
Other articles by Toussaint (Overcoating the Caruthersville Bridge, JPCL, May, p. 47, 2010) and the 2008 SSPC Proceedings by Chong, Yao, and Lee (“Early Test Results of One-Coat Systems Applicable to Steel Bridge Structure”) are not so clear on which type of CSA coating is used and thus a casual reader might not perceive the difference.