Conservation Works of the US Capitol Building

by Peter Cox, Manging Director, Carrig Conservation International Ltd. 

Source: FEMA photo library

In the 1980s a large piece of stone fell off the US Capitol Building, initiating a study to determine the cause. The Masonry Stabilisation Services Corporation (MSSC) who I worked for at the time was commissioned to carry out an investigation.

The center section was built using a Brownstone which is a sandstone and brown in colour. Within 20 years or so the state capital architect discovered the sandstone was weathering badly so he ordered it to be painted white – in the mid-19th century the Senate and library wings were added, and they were clad in white marble to match the white paint.

When we analysed the paint there were 30+ coats on there because of the frequent freshening up of the pain for the inauguration ceremony. All the paints were non-breathable and therefore trapped moisture within the soft sandstone. With the freeze thaw process the moisture freezes, expands and causes physical damage to the stone but in most cases, this is hidden by the paint.

Our recommendation was to remove the paint which we did using a ProSoCo paint remover specially designed to remove multiple layers of paint – the stone was inspected and was in very poor condition. We carried out a desalination process and then chemically consolidated the stone but now we had a reverse “Badger” two white wings and a brown stripe down the middle.

We had to paint it again so working with the German chemical company Wacker and ProSoCo, we developed the Breathable Masonry Coating system (BMC). This paint is 90+% breathable and therefore does not deteriorate like other paints – I believe this system has only been touched up once in the last 30 years and has survived many inaugurations.

Today we witness a truly unusual inauguration and doesn’t the building look well – proud to have been a part of history!