Fastener Finishes and What Salt Spray Hours Really Tell You

The fifteen

Plain, zinc plated, colour zinc, blue zinc, white zinc, black zinc, black phosphate, grey phosphate, black oxide, dacrotized, Ruspert, Xylan, nickel, bronze and spray paint.

Salt spray is comparative, not predictive

Across this catalogue, salt spray test time runs from 24 to 2000 hours depending on material and finish, and reaches up to 3000 hours on the stainless self drilling line. Those are laboratory hours in a cabinet. They rank finishes against one another reliably; they do not convert into years on a building, and anyone who tells you they do is selling something.

The three blacks

Black oxide is a conversion coating with an oil film — essentially appearance. Black phosphate holds oil and paint and adds modest protection. Black zinc is a real zinc coat under a black passivate and is the only one of the three with meaningful corrosion life. They are indistinguishable in a photograph.

The zinc passivates

Colour (yellow), blue, white and black zinc are all zinc coats under different passivate layers. The passivate changes both appearance and corrosion life; yellow passivate has traditionally been the most protective of the common ones.

When to go past zinc

Dacromet, Ruspert and Xylan are the systems to reach for when the fixing has to stay outdoors for years and stainless is more than the job needs. They are where the upper end of the salt spray range comes from.

Thickness is part of the specification

A finish name on its own is half a specification. On the black bugle head line the plating can be laid down at 15 microns, which is thick enough to carry the anti-corrosion duty rather than only colouring the screw.

Everything on this page describes the specification range Beyond Industry Groups Limited works to. Where a figure is a laboratory test result rather than a service life, it is described as such.