IRS Overfinish Removal from 1930s Lacquer
Washington, DC: 2006
IRS Headquarters in DC was constructed in the 1930s and many of the rooms are paneled in mahogany with nitrocellulose lacquers. Sometime in the last few years an attempt to "spruce up" the rooms with an overcoating of dyed varnish went wrong. The finish had separated into islands of pigment, causing a spotted leopard appearance. This was likely the result of adding too much dryer to the varnish in an attempt to speed the drying to within a few hours so the work could be completed overnight or in a weekend as is often required on occupied buildings.
GSA now wanted the rooms refinished, but the conservation team countered that it might be more practical to just remove the recent finish, leaving either the original nitrocellulose as the presentation surface, or using it as a sound surface for the application of a new finish. Stripping rooms back to bare wood requires significant surface preparation and re-sealing of the wood that is unnecessary if there is an earlier sound layer. We sought to bypass these extra steps and work with the original surface, which would cause considerably less disruption in the rooms and would be more cost effective for the government.
Selective finishes removal is not a one-size-fits-all approach like many strippers on the market that are strong enough to strip nearly everything in their path. The development of these targeted gels comes from fine arts conservation for removal of overfinishes on rare and valuable artwork. First the stratigraphy of the materials in each layer is determined by florescence microscopy and then, knowing the constituency of each layer and its condition, decisions can be made about which layers to strip back. Once it has been determined which layers will and will not be removed, it is possible to choose the right solvents to attack only the layers to be stripped.
Ethanol was the appropriate for this oleo-resinous varnish (although it had to be used with care because too much dwell time could affect the underlying lacquer). The ethanol was gelled in Carboset and Ethomeen using formulations developed by Richard Wolbers. Troweled on, covered with plastic, and allowed to dwell 45 minutes, the varnish was swollen enough that it could be easily lifted off with plastic spatulas, although scotchbrite pads were used to gently lift it out of molding profiles. The surface was wiped down one last time to lift any residue using cotton rags touched with a bit more alcohol. After all the varnish was removed, GSA found they liked the original nitrocellulose layers and chose to simply have some dark wax buffed into the moldings to give a bit more warmth and depth to the presentation, instead of adding another finish on top.
Since solvents are fairly volatile and would evaporate quickly, as well as be potentially flammable in the air, they are trapped in a simple gel to stop evaporation. Trapped in a gel, the solvent cannot evaporate and therefore is also virtually odorless. IRS was a benchmark project for the federal government to see that a selective stripping project can be quicker, cheaper, less disruptive, and even healthier for the finishing crew and building occupants than conventional stripping to bare wood and refinishing methods.