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Corrosion Clean-up

Posted By:
Michael Saathoff
18
Posts
0
#1 Posted: 4/13/2010 15:10:17


Greetings,

I'm recovering/rebuilding A Stits Playmate and currently in the process of working on the wings. http://stitsplaymate.blogspot.com.   It looks like the original metal wing bracing was painted with zinc chromate and has some light corrosion in a few places.  This bracing was not designed to be easily removed so the idea of removing and sandblasting isn't very palatable.   I was thinking of some light sanding by hand, one coat of Gemplers rust conversion and then a coat of fresh zinc chromate.  Anyway, I thought I'd bounce this idea off of some of you with way more experience than I and see if my approach was the best way to go.  Any thoughts on dealing with this light corrosion would be greatly appreciated. 

I attached the photo below to give everyone an idea of what I was working with...Yes I know the rib is cracked but that's another post.  :-)

 

wing bracing.JPG 



Alan Leaning
6
Posts
1
#2 Posted: 4/15/2010 20:47:06

Hi Mike,

Personally I don't like the idea of using a rust converter on aircraft or structural items - especially on an area that in the future is going to be inaccessible. That's just me. My main question, are the brace wires pitted and how do they look at the anchor points? If the surface rust can be removed with something like a scotchbrite pad and shiny metal exposed as a result, then after cleaning a nice even coat of a good quality primer should do.  What I CAN see in your photo doesn't appear to be too bad. If the wires/rods are pitted, consider replacing them.

Good Luck.

Alan

 

 



Bob Matteson
Young Eagles Pilot or VolunteerHomebuilder or CraftsmanAirVenture Volunteer
2
Posts
1
#3 Posted: 4/18/2010 16:28:15

Mike,

I agree with Alan, if you can clean it up with a scotchbrite pad and there is no pitting, it should be fine.  Rust converters are not something I would really  like to use on something like that.  A good coat of epoxy primer should do the job.

 

Bob



Bob M.
Michael Saathoff
18
Posts
0
#4 Posted: 4/18/2010 22:24:48

Some people thing rust conversion coating is the best thing ever and other folks can't stand it.  I was wondering if you could elaborate on your concerns?  Not saying your wrong...I'm just wanting to learn.


Thank You,


Mike Saathoff



Alan Leaning
6
Posts
1
#5 Posted: 4/22/2010 20:45:37

Mike,

I feel rust converters were conceived for uses OTHER than aviation. It may be OK for use on that rusty hangar door or lawn mower - I used it years ago on the bottom of a motorcycle tank with good results. I'm an A&P and in my 30+ years in the industry I don't remember having seen the recommendation of a 'rust converter' in an aircraft or component maintenance manual.  I've used approved conversion coatings on bare aluminum and magnesium alloys after cleaning, they are always washed off and dried before, at a minimum, coating with a good quality primer after treatment. Corrosion work is time/labor intensive. What you have is a structural item in what will become an inaccessible area. One should consider the prospects over time if things don't go the way they are expected. That's me~

Alan 



Bill Berson
Homebuilder or Craftsman
106
Posts
19
#6 Posted: 4/26/2010 19:43:03

 Some Ospho (phosphoric acid steel treatment) on a rag will remove light surface rust nicely. And the Ospho treatment is a good prep for primer as well. My hardware store sells Ospho.



Richard Warner
Homebuilder or CraftsmanAirVenture Volunteer
32
Posts
2
#7 Posted: 6/8/2010 18:57:29

Hi Mike,

    I am an A&P(39 years) with I.A.(26 years), and must admit that I have used a rust conversion coating on a few aircraft parts for the amphibian I built over 20 years ago.  That airplane is still flying, by the way.  I would hesitate to use it on highly stressed parts.  I find that it only converts the very top of the rust unless you clean down to bright metal for the most part.  Otherwise after allowing it to dry, if you sand it, you will again see rust. The Ospho (phosphoric acid steel treatment) mentioned in another post is one of the names of rust conversion coating.  There are other brand names for the same stuff.  Chem-Prime is the one I'm familiar with. It is phosphoric acid too.  The first time I saw this stuff, we sanded a piece of steel and then put some on it where we had sanded and put it out in the weather with no other protection on it.  After 2 years, there was only a very small bit of rusting where it had been applied.  When you get down to it, the airplane is experimental, so legally, there wouldn't be anything against using it.