What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Chipped Primer

D

DarinFred

Active Member
Well, I primed my HS parts on the 4th and now I am starting to put them together. Today I riveted HS609PP to 603PP and I noticed that when I squeezed the rivet, the primer chipped around the shop cranium. Anyone think this will be a corrosion problem down the road? I'm content with pressing with the build, but if it will cause problems down the line, I think I might touch the chips up with extra primer. Any suggestions or words of wisdom?

Jay
 
I am guessing that you aren't using a self etching primer or your substrate wasn't clean.

A grey scotchbrite hand pad with dish soap and water will provide an adequate solvent cleaning job and adhesion profiling for your needs. Try that first. The surface of the alclad needs to be scuffed for good adhesion.

I would scuff the painted parts that are having the detatchment problems, clean with thinner and recoat with self etching primer if I were you.

...or you could just assemble them!

:D CJ
 
DarinFred said:
Well, I primed my HS parts on the 4th and now I am starting to put them together. Today I riveted HS609PP to 603PP and I noticed that when I squeezed the rivet, the primer chipped around the shop cranium. Anyone think this will be a corrosion problem down the road? I'm content with pressing with the build, but if it will cause problems down the line, I think I might touch the chips up with extra primer. Any suggestions or words of wisdom?

Jay
Click to expand...

This is a good argument for :
Etching
"Alodining"(chromic converting)
AND using a two part milspec epoxy primer.

I starting the fuse, and I can tell you that I do not have one chip of primer off the whole airplane thus far.


Peter
 
What kind of prep did you use before applying the primer?

I clean and scuff the parts before applying a self etching primer and don't have problems with flaking. I do sometimes nick parts (especially with a bucking bar). I give the parts one more hit with the primer and move on.
 
I'll submit that, no matter what primer system you are using, if you noticed a chip, you're applying it too thick for our application of basic corrosion protection. (unless the surface prep was so bad that...)
 
Lesson learned I think

I'm usingthe whole scuff, etch, alodine then 2 part mil spec primer process. The primer cracks around the rivet when I squeeze it. I've narrowed it down to 3 possible root causes.

1.) I really didn't scuff the aluminum all that much. Maybe I need to scuff it more, particularly around the holes.

2.) Bad air supply. I think the primer may have been contaminated from my compressor. There were quite a few fisheyes and I decided in the big scheme of thing to press and fix the problem later with a new air filter...a better one than the POS from Lowes.

3.) I was probably applying the primer too thickly. Being it was my first time priming, I figure this will get better as I move along.

Overall solution for the HS. I'm going to put it together as is and go back with a touchup brush and fill in the flakes with primer. I'm not worrying about it too much but I do realize that I suck at using a HVLP (although I finally got the gun dialed in as I was priming my last rib) and the whole priming process is a PITA.
 
Thin primer

DarinFred said:
I'm usingthe whole scuff, etch, alodine then 2 part mil spec primer process. The primer cracks around the rivet when I squeeze it. I've narrowed it down to 3 possible root causes.

3.) I was probably applying the primer too thickly. Being it was my first time priming, I figure this will get better as I move along.

The spec for Boeing BMS10-11 two pack epoxy primer calls for 15-25 micron. A lot of builders think that the idea is to spray on the primer so thin that it is virtually transparent....that is not 15-25 micron...it's closer to 5 micron and will not provide a reasonable protection against corrosion. At 15-25 micron you will not see the substrate through the paint.

You may have the primer too thick but I doubt it. Adhesion problems are more likely related to inadequate preparation.

Degrease, scotchbrite, acid etch, alodine and prime (BMS10-11) is the ultimate internal priming process. Nothing beats it. But....there are a lot of stages and each one needs to have specific quality control. The problem is that not many builders go to the trouble of actually obtaining and reading the specs for the products they're using.

For example Alodine should be used for immersion at 24-30 degrees C (a cheap aquarium heater works well). And after acid etching you should never let the surface dry off before it gets rinsed....minimum 15 minutes dip rinsing in running water....etc etc.

The best thing is to run a test piece through with each batch and test it before you rivet all the components into your plane. You should test for adhesion (2mm cross hatch test with tape) and chemical inertness (10 second wipe with MEK). Then you can be confident.
Click to expand...
Click to expand...
 
I did the tape test and it didn't peel anything off. Also, MEK does nothing to the surface. It's tough as nails, it's just chipping around the shop head. I tend to be a perfectionist, so its bothering me a little. I'm over it now and worry about the blind rivets I had to use to secure a drilled out HS404 to HS702 and HS405! :)

Jay
 
I've built my whole plane with the following process: Wipe down with acetone or laquer thinner, acid etch for about 3 min, alodine for about 3 more, air dry, 2 light coats Akzo. Never had any kind of adhesion problem. I wouldn't get too worked up about it though. My guess is it's going on too thick. I see another post that recommends 15-25 micron which is equivalent to .0006-.001 inch. This sounds about right, but I do believe that at .0006 you would be able to see through it somewhat.

How many coats are you using and of what? I'd say one coat or a light tack coat followed by a light coat should get the job done. Like I said though, don't get too worked up and BUILD ON!
 
Proper adhesion testing

DarinFred said:
I did the tape test and it didn't peel anything off. Also, MEK does nothing to the surface. It's tough as nails, it's just chipping around the shop head. I tend to be a perfectionist, so its bothering me a little. I'm over it now and worry about the blind rivets I had to use to secure a drilled out HS404 to HS702 and HS405! :)

Jay
Click to expand...

This is how you do a proper adhesion test. Get a Stanley knife and scribe straight lines through the primer to base metal. The lines should be at 2mm centres (or close). Do about a dozen lines. Then do the same thing again over the top of the scribed lines at 90 degrees. This should leave you with approx 120 little 2mm x 2mm squares. Wipe the area clean with some methylated spirits and let dry. Then apply a reinforced fabric packaging tape (this is a strong tape with a high level of adhesion...ordinary clear tapes are usless). Squeeze it down and leave it for 24 hours. Then pull it off violently.

If no squares come off then you have the ultimate adhesion. If you lose a half a dozen squares it's still a pass. If you lose half your squares you have a problem.

It is not recommended that you do this test on a aircraft component because scribing the aluminium is bad (can lead to cracks forming). That is why I recommend you run a test piece through with every batch.

Placing a piece of tape on the primer without scribing and just pulling it off reveals nothing....except that if it pulls any primer off you have a really monumental problem. But in reality even primer with very bad adhesion can pass such a test.
 
You must log in or register to reply here.
Back
Top