Longfellow bridge, massdot

The Longfellow Bridge connects Cambridge to downtown Boston. Longfellow Bridge is a historic bridge, which meant preserving much of the original design.

The original design made use of rivets, something you don’t see often in bridge construction today. Working with the fabricators and GC, we needed to find how coatings would fit into the critical path, but also meet the MassDOT Bridge Coatings Spec.

Primer, Interzinc 22HS

The selected manufacturer for the Longfellow Bridge project was International Paint. The selected primer was International Interzinc 22HS. However, this was only the first primer. This inorganic zinc rich coating was applied to components, like lattice bar, channel and angle before riveting took place.

The objective was to get a zinc rich primer in between the faying surfaces of the support columns before access was restricted by riveting.

More Primer, Interzinc 315B

Because the 22HS alone is a thin coating and wouldn’t provide the maximum amount of corrosion protection, after columns were assembled at the fabricator they were returned to our facility for a full coat of International Interzinc 315B. Interzinc 315B was acceptable to overcoat 22HS because it is an organic zinc rich primer.

Mid Coat, Interguard 345

The mid or tie coat for Longfellow Bridge was International Intergaurd 345. Like every coat, it was crucial to apply a proper stripe coat before the full spray coat.

Complex structures present many application difficulties. Dry-spray is a constant battle. Additionally, being sure to not overcoat while spraying edges can be challenging. A proper stripe coat, applied with brushes, rollers and spray stripe is necessary for a quality product.

Top Coat, Interfine 979

International Interfine 979 was the selected top coat. This product offered UV protection with superior gloss retention.

The Interfine 979 had two attributes that made it unique for a shop application.

The product tended to behave like glass. On normal material handling impact, it was less likely to scar the way you would expect a polyurethane, but rather chip like glass. This made touchups bothersome.

Additionally, the top coat had a “spotted leopard” effect in that areas receiving touch up were visually obvious as the colors didn’t match. Many times, this meant recoating an entire component to blend in touchup.


The project went well and when complete, the bridge looks amazing. Working with the system was an experience and the curveball of riveted construction certainly presented unique challenges. Like many projects it was difficult, but well worth it.