[R-390] Painting Knobs

[Barry]

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