[R-390] Painting Knobs

[Barry Scott]

Red front panel.  Green knobs.  A Christmas-tree R390.  I like it!

Thanks,
Barry - N4BUQ


On Fri, Aug 16, 2024 at 12:13 PM Thomas Hoyer via R-390 <
r-390 at mailman.qth.net> wrote:

>  Knobs should be black, not green............. Sorry, couldn't resist.....
> TomW3TA
>     On Friday, August 16, 2024 at 12:34:55 PM EDT, Barry <
> n4buq at knology.net> wrote:
>
>  Jacques,
>
> Yes, I've looked around for primers for zinc and, while it's a bit on the
> expensive side, I may have to go that route.
>
> For the knob that failed the last scratch test, I dunked it in the acetone
> for a while and, surprisingly, while the top coat fell off (as expected),
> the primer did not.  The self-etching primer fell right off in the acetone
> so I think this is a step in the right direction.
>
> Before ordering the special zinc primer, I'm going to try this primer
> again, let it dry longer (and hotter), apply the top coat and also let that
> cure longer (and hotter).  It may simply have been that the top coat was
> still too green.
>
> Thanks!
> Barry - N4BUQ
>
> > 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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