Priming - Does all of the Alclad need to be removed?

[Lou]

I'm at the point where I need to dress up the interior of the horizontal stabilizer skins prior to assembly. Does all of the alclad need to be removed prior to priming or can I just scuff up the surface with a scotchbrite pad? I plan on smoothing out any scratches with the pads and I'm sure that in those area's all of the alclad will be removed. I have been using Mar-Hyde rattle can with excellent results on the ribs and spars. I also have the Stewart Systems primer which I have not used yet. I would like to give the SS Eko Prime a try, but I'll need to spray that (another first for me). If I prep the scratched up areas properly and then scuff up the rest of the interior skin and shoot it, will the light scuff work without entirely removing the alclad on the rest of the interior skin?

My other option is to fully prep and rattle can the scratched up areas where the ribs and spars attach and then dress out any minor scratches elsewhere and treat with an alodine pen.

 

[jsharkey]

No!

I'm at the point where I need to dress up the interior of the horizontal stabilizer skins prior to assembly. Does all of the alclad need to be removed prior to priming or can I just scuff up the surface with a scotchbrite pad? I plan on smoothing out any scratches with the pads and I'm sure that in those area's all of the alclad will be removed. I have been using Mar-Hyde rattle can with excellent results on the ribs and spars. I also have the Stewart Systems primer which I have not used yet. I would like to give the SS Eko Prime a try, but I'll need to spray that (another first for me). If I prep the scratched up areas properly and then scuff up the rest of the interior skin and shoot it, will the light scuff work without entirely removing the alclad on the rest of the interior skin?

My other option is to fully prep and rattle can the scratched up areas where the ribs and spars attach and then dress out any minor scratches elsewhere and treat with an alodine pen.

The Alclad is a layer of almost pure aluminum that is virtually corrosion proof. Leave it be. Use one of the etching preps from Dupont or Stewart before alodining and/or priming.

Jim Sharkey
RV6 - Phase 1

 

[Lou]

Just prime along the rivet lines (or not)?

Sounds like a good plan and a lot less work.

Should I just address the scratches only or prime along the rivet lines on the inside as well? My DAR had suggested using just an alodine pen to treat the scratched areas. I picked up a Touch-N-Prep Alodine 1132 pen from Spruce.

I suspect that all the scratches will still need to be dealt with regardless.

 

[RudiGreyling]

Sounds like a good plan and a lot less work.

Should I just address the scratches only or prime along the rivet lines on the inside as well? My DAR had suggested using just an alodine pen to treat the scratched areas. I picked up a Touch-N-Prep Alodine 1132 pen from Spruce.

I suspect that all the scratches will still need to be dealt with regardless.

YES At minimum deal with scratches you think has passed the alclad layer.

The rest of the priming is your preference, and open to debate and warfare.

If you do decide to prime, then creating a 'key' with scothbrite helps with primer adhesion. All you want to do then is dull the shiny surface, NOT TAKE OFF THE ALCLAD.

Good Luck,
Rudi

 

[Lou]

Thanks guys - I'm back on track

Thanks for the education, it's exactly what I needed. I'm scared to death of corrosion and would rather invest in the preventative measures if needed rather than the cure later. I'll dress the wounds, treat and leave the rest alone.

P.S. I should have listened to the group and left the dreaded blue stuff on. Another painful lesson learned.

Thanks again,
Lou

 

[rbibb]

One point regarding priming, alodine, etc.

Alodine is a chemical conversion process that converts any corrosion (aluminum oxide) on the surface of an aluminum alloy to an inert compound preventing further corrosion. As such it, in effect, etches the surface of the aluminum.

Etching primers (so called wash primers) also etch the surface.

Other primers, (epoxy based, etc) do not etch the surface.

As far as surface prep:

If you are going to alodine or use an etching primer I do not think it necessary to scuff or scotchbrite pas the surface as the alodine or etching primer will do so. In fact, if you use one of the phosphate acid wash preps (alumniprep, for example) the phosphate acid etch will etch the surface as well.

Scratches must be buffed out not as preparation for paint but to remove potential crack-inducing stress risers. On alclad skins preping the scratches removes the alclad exposing 2024 aluminum which needs to finished (alodine, prime, or both) to prevent corrosion.

On the interior of our planes I suppose you can get away with using an etching primer after an alodine treatment however, a long time painter I use for this process for industrial usage swears never to use an etching (or wash) primer over alodine before a final top coat as the top coat will not adhere properly and will come loose sooner as a result.

In many cases for mil spec parts alodine is the final finish spec for aluminum parts that are not going to be directly exposed to the outside or, in the case of many interior aircraft parts, alodine followed by an epoxy primer.

The combo never seen is alodine followed by an etching primer.

Just food for thought as to what to do with your aircraft parts.

 

[Lou]

It's all starting to click. Thanks for mentioning the caution on not using the self etching primer over the alodine. I was going to do just that. I've got a better understanding of the process now and it's all starting to make sense.

No primer war - life is good!

Thanks again to all,
Lou