Paint question for Johnny!

[mbweimar]

And anyone else who may be able to help...

I recently read Johnny's thread in the hobby section about his years in the Navy, and sign painting business...So Johnny this question is geared towards you, but I'm open to any and all advice!

As y'all may have seen, I got some fab work done for my Weldbilt project. It turned out great, but there are four spots where he welded to the back of a painted surface. You can probably guess that the paint bubbled up on the outside...Which is understandable. He had to weld there.

So...Now to recoat. The two part epoxy primer that was used is about $40 a quart and I only need a tiny bit, so I won't be using that. I do however have some spare 1 part water based metal primer that was recommended for use with my rubberized nonskid. The directions state that bare aluminum must be acid washed with 1 part muratic acid, and 1 part water. So my question is, will the muratic acid mix hurt the surrounding paint? If so I guess zinc chromate will be a better option. Here's a few pics of what I'm working with.


I'm not sure why my phone decided to filter this pic but here are the welds on the inside.


And the outside. I sanded the bubbles out with 80 grot, then smoothed everything out with 220.
I'm off work tomorrow, so I'm hoping I can get some ideas how to prime these spots. Thanks guys!

 

[Johnny]

edit: after going back to look at your photos again, I see paint that appears
to have been discolored by the heat. all of that area has been compromised and "may"
have lost its purpose of protecting the aluminum.
all the discolored material must be removed, cleaned, etched, primed and repainted
with your method of choice.

QUICK wash with the acid - don't let it sit for over 3 seconds.
rinse well - very well - baking soda rinse - rinse again.
- or - skip the harsh approach and just use plain straight vinegar.
From what I have read, self etching primer is for bare metal ONLY.
One should avoid painting over existing paint with S.E.P. as it "may"
tunnel under the existing paint creating an avenue for corrosion.
just plain metal primer - repaint - go enjoy your boat !!!!

ensure you have removed all traces of oil, grease, etc prior to etching and priming.
if you get fisheye or orange peel effect, and it bothers you, strip it and do over again.

 

[mbweimar]

Thanks Johnny! I forgot all about vinegar. I have some scrap pieces of aluminum I can test with before hand.

I may also insider a Q-tip with the acid mix to avoid it running down the paint.

This forum is definitely a better place with you here Johnny.

 

[Johnny]

thanks for the flowers - - - - -

but

this forum is successful and enjoyable through a Team Effort.
many, many, many very talented members here willing to help.

in my field, we have a motto: "see one - do one - teach one".

so in the future if you see the same question asked by a new member,
it will be your turn to offer your first hand experience to the issue.
come back in 6 months with an update of how it is all holding together.

 

[mbweimar]

I certainly will pass the knowledge along. My forte is electrical, so I often visit that part of the forum to share my experience.

The discoloration you see is the primer. It's dark gray in color, then the light gray top coat was sprayed on top of that. I failed to mention the first step I took was using a brass wire wheel on a drill to remove everything that separated from the substrate.

I successfully used a Q-tip with a slightly stronger muratic acid/water mix to etch the bare aluminum. No dripping, no mess. The bare spots are only about 4x2".