Ask the Expert Question-and-Answer Archive

by Ron Joseph

January, 2002

Paint and Coating Failures On Bridges

Q. Is there a way to gauge the probability of paint failure as it relates to steel bridges. Specifically, of near white to white metal blast, 3 coats? (1st coat is XincClad HS II, 2nd coat is Epoxy Mastic Aluminum II, 3rd coat is Highsolids Polyurethane.) I am specifically looking at failure rates in the first 10 years.

A. Thank you for your email. As you can well imagine the risk of failure will depend on many factors, including surface preparation, coatings used, manner in which the coatings are applied, intercoating times between surface prep and application of the primer, intercoating times between the discrete coatings layers, and of-course the environment to which the bridge steel structure is exposed. Some of the steel components will be more vulnerable to failure than others. The coatings suppliers should be able to give you some case histories based on the data that they have gathered over the past years. You might also be able to get useful data from the Structural Steels Painting Council (SSPC) located in Pittsburgh, PA (www.sspc.org). Ultimately, you might need to perform your own accelerated weathering tests by sending coated panels to an accredited laboratory. However, even in this case you will need to make a number of assumptions if you wish to correlate accelerated tests with real-time exposures.