Metal finishing Q&As since 1989

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Can I put a top seal on a previously zinc plated self-tapping screw?

May 12, 2011

Any issues with adding a top seal (Super seal or equivalent) on a existing zinc plated self-tapping screw? Or do I need to strip and replate the fastener?

The self tapping screw has a carburized case and I am concerned about potential hydrogen embrittlement. Would prefer not to have to deal with this in a foreign country when I have little control over the process.

Time and risk are critical and would prefer adding a top seal rather than reworking. Thanks!

Mark Bauck
Product Designer - Coon Rapids, Minnesota, USA

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Hi, Mark.

It probably depends on what's wrong with the screws. If they are simply exhibiting too short a life before rust or corrosion sets in, anything you add on top will probably somewhat improve the situation. But if the plating is peeling, it will just take the topcoat with it; a topcoat is not shrinkwrap :-)

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 12, 2011

I am afraid of applying top coat over passivation. If the fasteners are plated a long time back already moisture would have penetrated the surface and deterioration would have started. If applied now it will be entrapped inside. Maybe you can dry the fasteners, cool it and apply top coat as soon as it cools down.

S.V. Aurobind
plating process supplier - Bangalore, India
May 17, 2011