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The 4m filament-based coating chamber at the Canada-France-Hawaii Telescope (CFHT) has been in service since before first light in 1979. Even then, the chamber produced thinner coatings than were desired - a problem that continued to plague the facility for the next forty years. Over that time the stripping and cleaning procedure was improved, as was the procedure for maintaining the coating while in service, but efforts to improve coating thickness had so far fallen short. In 2019, after forty years of continued use, cracking in the filament electrodes necessitated modifications to the chamber. These were completed in 2020 along with an overhaul of the chamber's vacuum system and thickness monitor. When the test-fire of the chamber again produced a thin coating, we took the opportunity to take a fresh look at possible underlying causes so that we could attempt to address them prior to the next mirror coating. The work was completed just in advance of the 2020 coating of the CFHT M1. Both the test-fire and the M1 coating exceeded 1000Å thickness, a first for CFHT. In this paper, we share details of the renovations to the chamber, the findings of the thin coating investigation, the further changes we made to the chamber to address them, and the resulting coatings.
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