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Bridge Coatings: More Than Just a Color

Have you ever thought about the coating on a bridge? Wondered if it’s paint just like you’d use for your house, or if it’s painted simply to give the bridge some color?

The paint on a bridge is, in fact, essential to the integrity and lifespan of the bridge. It is a much denser paint system with several more layers than you’d use for your house, and it helps prevent corrosion of the bridge itself. Just as you use clothing and sunscreen to combat the sun and other weather conditions, bridge coating systems help protect our nation’s bridges, ensuring their longevity.

Coating a bridge is a careful, multistep process. Most of the bridge coatings we deal with at Modjeski and Masters are pre-existing and we are concerned with risk mitigation. We assess and address coating life as well as performance against different environmental exposures.

We begin with an inspection to determine the condition of the existing coating system and the extent of any corrosion. Next, we remove the existing coating using a blast hose, which is a high air pressure -powered hose that propels an abrasive agent against the surface to remove the coating and create a surface profile to help anchor the new coatings. Older coatings are often lead-based and may contain other potentially hazardous or harmful chemicals, so during the removal process the crew must wear protective gear and follow proper containment procedures to ensure neither they nor the environment are harmed. 

Removing the existing coating does come with surprises. We’ve come across peregrine falcons, owls, cats and other lost animals and significant loss of metalwork section. We make a lot of discoveries while blasting.

Applying the new coating is another process that involves balancing a number of factors (such as temperature, dew point, relative humidity, wind, and surface temperature of the bridge) to determine when to paint, how long to let each coat dry before applying the next one, and how long the coating needs to cure before it can be overcoated. 

And we can’t forget about color selection. While we typically recommend colors that align with history or the surroundings, such as blue for a bridge over or near water, brown for a bridge in a wooded area, or black for bridges along a rail system, the decision rests with the bridge owner or the pubic. Color, just like the integrity of the coating, fades over time—Mother Nature is unstoppable—which is why it is so important to maintain coatings.

Coating projects are always challenging; every day of the job is different and presents new obstacles or constraints. Once the project is completed though, you have the satisfaction of knowing everything was done properly and you’ve helped make the bridge safer and last longer.