[R-390] Painting Knobs

[Les Locklear]

Zinc Chromate Primer. It’s available in rattle cans.

Les Locklear

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________________________________
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Jacques Fortin <jacques.f at videotron.ca>
Sent: Friday, August 16, 2024 11:01:15 AM
To: 'Barry' <n4buq at knology.net>
Cc: 'R-390 Mailing List' <r-390 at mailman.qth.net>
Subject: Re: [R-390] Painting Knobs

Barry, it depend on the primer you used.
I know that there is specific primers for Zinc (yellow or light green in
color as far as I remember) and yes, heat curing can only help as I believe
that your actual problem is primer adhesion.
There is many things that surface up on Google when you search for "Primer
for zinc surfaces"

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : Barry <n4buq at knology.net>
Envoyé : 16 août 2024 11:30
À : Jacques Fortin <jacques.f at videotron.ca>
Cc : R-390 Mailing List <r-390 at mailman.qth.net>
Objet : Re: [R-390] Painting Knobs

Jacques,

I allowed the primer to dry overnight, painted the top coat, set it in the
sun for a couple of hours to help the curing process, let it sit overnight,
and then tried the scratch test.  I'm not so much concerned about the top
coat being all that hard at that point but I am concerned that the primer
doesn't want to stick to the metal.  I wouldn't think the primer needs heat
curing to stick, would it?

Thanks,
Barry - N4BUQ

> Barry, IMHO, if you tried a "fingernail test" just few hours after the
> knob was painted, it is normal.
> Most paints can take a week or more to harden.
> The trick I used was to put mine under the summer sun once they were
> painted with the Krylon Dual-superbond, and they were "holding" such
> fingernail test.
> You can also use a small oven at 200F to promote the paint hardening.
>
> 73, Jacques, VE2JFE in Montreal
>
> Welp, I give up.  I tried priming one knob with a non-etching primer
> and a top coat.  I can take my fingernail and easily scratch the paint
> off down to the bare metal.  Sigh... Maybe I'll have them chrome plated.
>
> Thanks,
> Barry - N4BUQ

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