Painting the Bridge

April 1935, Irving Morrow’s Report on Color and Lighting

Why is the Bridge Painted International Orange?

What is the Color Formula for Golden Gate Bridge International Orange?

There are a couple of misconceptions about how often the Bridge is painted. Some say once every seven years, others say from end to end each year. The truth is that the Bridge is painted continuously. Painting the Bridge is an ongoing task and a primary maintenance job. The paint applied to the Bridge’s steel protects it from the high salt content in the air which can cause the steel to corrode or rust.

As the Bridge was built, it was painted International Orange, with a lead primer and a lead-based topcoat. Painting of the various Bridge structures then continued into the next several years. Spot painting of the steel continued in various areas of the span on an as needed basis until 1968.

By 1968, advancing corrosion sparked a program to remove the original lead based paint (primer and topcoat) and replace it with an inorganic zinc silicate primer and vinyl topcoats. This process was completed in 1995. Note that in 1990, the topcoat was changed from a vinyl to an acrylic emulsion to meet air quality (Volatile Organic Compounds or VOC) requirements.

Painting continues today and is based on priorities which are determined by inspections that assist in determining where the corrosion of the steel is advancing. In 2012, there were two major paint projects along with touch-up projects - repainting the two main cables and the painting of the north approach viaduct structures.

Painting During and After Original Construction

From the Fiscal Year 1938/1939 Annual Report:

“The largest item in the maintenance budget is for painting of the structural steel. The past fiscal year, the sum of $112,431.84 was expended for painting of the Bridge structures. This amount was divided as follows: Labor, $86,589.13; brushes, tools, etc., $5,430.67; paint, $20,412.64.

“The exposure to salt-laden fog is more severe at the Golden Gate than any other bridge in the Bay Area. Not only is the fog extremely active in attacking the paint film but it also limits the hours when painting can be done. Over thirty percent of the working hours during the last fiscal year could not be utilized for outside painting because of weather conditions.

“The condition of the paint on the steelwork was so critical at the time of the Bridge opening that an acceleration of the original painting program was necessary. This situation arose because two conditions were not thoroughly understood at the time the original estimate of operating costs was made, namely (1) the severity of exposure and (2) the importance of special treatment of the steel surfaces prior to erection. On steel structures erected subsequently to the Golden Gate Bridge, steel surfaces have been treated by sandblasting or flame cleaning prior to erection. Failure to use either of these special treatments has added greatly to the cost of maintenance painting. The six months’ delay in the construction of the Bridge also contributes to this additional cost since, at the time the Bridge opened, the main towers, or over forty percent of the tonnage had already an exposure of one year. Prior to completion of the Bridge, contractors and the District found it necessary to expend over $130,000 for paint maintenance on the towers and main span.

“Immediately after the steel contractor completed his work in December 1937, the District organized a small crew of painters who had previous experience on the Bridge while working for the contractors. The crew starts at the bases of the towers where the rust had attacked the rivet heads and surfaces. The steel was thoroughly cleaned and a hot application of coal tar paint made at these points.

“The majority of paint failures has been caused by the loosening of mill scale. Rusting progresses under the loosened mill scale so that soon much of the surface is involved and it is necessary to remove most of the paint and thoroughly clean the metal surfaces. After trying the available methods of cleaning, the use of pneumatic chipping hammers with specially-made studite-tipped tools was adopted as being the most economical. After the rust and scale has been removed by chipping hammers, a flame dehydration torch is passed over the metal. The flame effectively dries out the moisture between the plates and around rivet heads and also removes all remaining traces of scale leaving a warm, dry surface to receive the priming coat. This surface is thoroughly wire-brushed and immediately primed while still warm and dry.”