Coating system for SP2/3

[damianyu]

If the steel surface can not be blast cleaned and surface can only be prepared to SP2/3, what would be the recommended coating system for corrosion protection? The existing coating is a 3-coat system with Zinc rich primer, epoxy intermediate coat, and polyurethane top coat.

 

[TugboatEng]

SP2 and SP3 are maintenance levels of prep for doing spot repairs. Without blasting to clean metal you won't see any benefit from using the zinc rich primer. Typically you'll use a brush or roller friendly epoxy, this may be the same as original coat.

There are a few low viscosity penetrating epoxies out there for poorly prepped surfaces. They're intended to be used as a pre-coat before your standard epoxy primer. These work well but they're messy.

 

[damianyu]

Since we are not repainting the whole bridge, this is a maintenance work. Does phenolic alkyd metal primer such as Kem Bond HS work for this purpose?

 

[hokie66]

You need a coating which is designed for maintenance work. Talk to coatings suppliers, Carboline and Porter for example.

This is my favorite for your type of work.

https://www.carboline.com/products/product-details/Carbomastic-15