v8bertha Posted May 24, 2007 Share Posted May 24, 2007 More metallugy questions... Where the roofrack sits in the gutters on the Camel the paint has become chipped in places and this is turn has caused moisture to get under the paintwork and make the Aluminium corrode. It's gone powdery in places which I believe is some sort of electrolytic reaction between 2 different metals? If this was steel work, I wouldn't worry too much, I'd just stick some "Kurust" on it, paint it and forget about it, but it ain't steel... So what is the best was to stop the corrosion from spreading? Is there a magic ally rust cure product on the market that works? Or should I just rub it down and paint over it in th ehope that it won't get much worse? Any helpful suggestions appreciated! Dan Quote Link to comment Share on other sites More sharing options...
rtbarton Posted May 24, 2007 Share Posted May 24, 2007 Rub all the loose paint off and remove the oxide with abrasive paper, paint the bare metal with etching primer and then finish with matching topcoat. Quote Link to comment Share on other sites More sharing options...
Les Henson Posted May 24, 2007 Share Posted May 24, 2007 Try and insulate the two metals from each other - thin rubber might work. It has to be non-conductive. Les. Quote Link to comment Share on other sites More sharing options...
Holyzeus Posted May 24, 2007 Share Posted May 24, 2007 IMHO its not rust just oxidization which ANY metal will do (trust me i'm a roofer.....) in contact with the air, so as per the reply from rtbarton good rub down and decent painting Quote Link to comment Share on other sites More sharing options...
Les Henson Posted May 24, 2007 Share Posted May 24, 2007 If the roof rack is steel and it gets into contact/close to alluminium, then there is a process called electrolytic corrosion, which makes the white powder. Alluminium will do this anyway over a period of time, but not as quickly. Les. Quote Link to comment Share on other sites More sharing options...
freeagent Posted May 24, 2007 Share Posted May 24, 2007 Its electrolytic/ galvanic corrosion.. Aluminium and steel are at different ends of the galvanic series, the ally will act as a sacrificial anode and rot away. as the others have said, sand it off, etch prime it and top coat it. the only way to avoid it is to insulate the two metals from each other, so there is no electrical path between the two... if you google galvanic corrosion i'm sure it'll tell you all you need to know..... Quote Link to comment Share on other sites More sharing options...
v8bertha Posted May 24, 2007 Author Share Posted May 24, 2007 Its electrolytic/ galvanic corrosion..Aluminium and steel are at different ends of the galvanic series, the ally will act as a sacrificial anode and rot away. as the others have said, sand it off, etch prime it and top coat it. the only way to avoid it is to insulate the two metals from each other, so there is no electrical path between the two... if you google galvanic corrosion i'm sure it'll tell you all you need to know..... ARGHHHHHH!!! Scary!! I googled, I read... And I understood!! The electrolyte (in this case water?) provides a means for the ions to move from the anode to the cathode (can't remember which way round, but one is a positive, the other a negative?) That kinda makes sense in my funny world Thanks chaps... Is etch primer available from Halfrauds? Quote Link to comment Share on other sites More sharing options...
rtbarton Posted May 24, 2007 Share Posted May 24, 2007 I buy my etch primer from a specialist auto paint supplier. It comes in two containers, one is the paint and the other phosphoric acid. The two are mixed, ratio depends whether you want to brush or spray. Quote Link to comment Share on other sites More sharing options...
Les Henson Posted May 24, 2007 Share Posted May 24, 2007 Nasty stuff to inhale, so be careful. Les. Quote Link to comment Share on other sites More sharing options...
western Posted May 24, 2007 Share Posted May 24, 2007 How we treat alloy corrosion on aircraft 1. remove all loose paint/corrosion back to clean bare material 2. treat cleaned area with a deoxidising solution Deoxidine 3. wipe area dry & coat with etch primer [Alochromate - water based, mixed 20% alochromate to 80% water] for 20 minutes until surface turns a light golden colour 4. wipe of excess with a water dampened clean cloth & dry area with dry non-fluffy cloth 5. apply coat of epoxy primer 6. apply final surface paint finish hth Quote Link to comment Share on other sites More sharing options...
Mark Posted May 24, 2007 Share Posted May 24, 2007 Thanks chaps... Is etch primer available from Halfrauds? Yep. Comes in an aerosol with Acid Etch written on the side... Mark Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted May 24, 2007 Share Posted May 24, 2007 and from halfords I think the tin says "Wicid acid etch innit" Nige Quote Link to comment Share on other sites More sharing options...
Jon White Posted May 25, 2007 Share Posted May 25, 2007 Bluddy tax dodging student........ Quote Link to comment Share on other sites More sharing options...
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