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  #1  
Old 09-15-2018, 10:37 PM
RyanB RyanB is offline
 
Join Date: Sep 2017
Location: South Africa
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Default Prime or Alodine Spars

Hi Everyone

I am at the stage of constructing my main spars. I have scuffed all the components and am ready to put some protection on them. I know that all premade spars from Vans are alodined, but I imagine this can be quite a mission at home as a massive bath will have to be made. Are there any downfalls I am missing regarding just priming my spar parts with a 2k primer?

Thanks in advance
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  #2  
Old 09-15-2018, 11:06 PM
terrye terrye is offline
 
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Location: Vancouver, BC, Canada
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Default Prime or Alodine Spars

Van's pre made spars are anodized which is an electrolytic process whereby a protective layer of aluminum oxide is created on the surface. For the size of the spars this is not a home process.

Alodine is a chemical process which creates a chromate conversion coating on the surface. It can be used alone or as a preparation for primer painting.

The paint manufacturer will advise on the best preparation for their product.

It's quite easy to make a "bath" for alodining. For the spar, I would use the box they came in, line it with poly film from Home Depot and use it to contain the Alumiprep/Alodine for the spar parts.
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  #3  
Old 09-15-2018, 11:19 PM
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az_gila az_gila is online now
 
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Quote:
Originally Posted by terrye View Post
....

It's quite easy to make a "bath" for alodining. For the spar, I would use the box they came in, line it with poly film from Home Depot and use it to contain the Alumiprep/Alodine for the spar parts.
I acid etched and alodined my -6A spars. It wasn't too difficult.

Make a wood tray and line it with heavy plastic as described above. I made a much smaller (narrower) tray with a plywood base and 1 x 2 sides to enable the job to get done with less fluid.

When it's alodined use a thin coat of a good epoxy primer to finish it off. Don't apply the primer too thick - on the -6 spar there are 14 layers of primer at the root. I imagine the -4 spars are similar.
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  #4  
Old 09-15-2018, 11:21 PM
RyanB RyanB is offline
 
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Default Primer

Thank you so much guys, would I be okay to just scuff and then prime without alodine? Sorry really don’t want to start a primer war��

Last edited by RyanB : 09-15-2018 at 11:33 PM.
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  #5  
Old 09-15-2018, 11:55 PM
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az_gila az_gila is online now
 
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Quote:
Originally Posted by RyanB View Post
Thank you so much guys, would I be okay to just scuff and then prime without alodine? Sorry really don’t want to start a primer war��
Maybe, but do the acid etch step anyway to help the epoxy primer bond. Just do the scuff step with maroon pads soaked in Alumiprep.
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  #6  
Old 09-16-2018, 12:55 AM
RyanB RyanB is offline
 
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Thank you so much Gil
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  #7  
Old 09-16-2018, 08:40 AM
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wirejock wirejock is offline
 
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Default Aluminum Oxide

Whatever method you choose, keep the time between scuffing or etching down to a minimum. Basically the time it takes to dry.
All that work removes the Aluminum Oxide as it should. It's the layer that keeps paint from sticking. It also starts reforming immediately. The sooner you apply something, the better it adheres.
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  #8  
Old 09-16-2018, 08:56 AM
Ron B. Ron B. is offline
 
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Default

If you wanted to paint an anodized part , how would you prep it?
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  #9  
Old 09-16-2018, 09:12 AM
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az_gila az_gila is online now
 
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Quote:
Originally Posted by wirejock View Post
Whatever method you choose, keep the time between scuffing or etching down to a minimum. Basically the time it takes to dry.
All that work removes the Aluminum Oxide as it should. It's the layer that keeps paint from sticking. It also starts reforming immediately. The sooner you apply something, the better it adheres.
Yes, but no need to trip over yourself running around.

This PPG data sheet talks about prepping aluminum for primer and mentions an option with acid etch but no alodine.

They use 24 hours as requirement from etch to prime.

http://www.ppgaerospace.com/getmedia....aspx?ext=.pdf
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  #10  
Old 09-17-2018, 05:47 AM
fixnflyguy fixnflyguy is offline
 
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Default Try this...

I work in the commercial jet MRO business and extensively with structures. Often, we have large parts or repairs that can't be alodined per the dip/submerged procedure that people are most focused on. Every single part of my -4 was alodined/primed during my build, and 95% was done by brush-on or wipe on. For instance, when building my spar, all parts were "washed" using red scotchbrite and soapy water which gives a "mechanical" etch. The acid etch is a method of "chemical etch"..both are accepted practice. After drying the parts, while wearing rubber gloves, simply use a cheesecloth rag and wet with alodine and wipe all the surfaces down, making sure complete coverage. Do not let the alodine dry. After a minute or two, wash it off with clear water. If the part is long or big such as skins, it can be done incrementally. The alodine is known as a conversion coating, and should be painted as soon as feasible after drying. Anodized parts can be given a similar light scotchbrite wash and then primed/painted. The parts that "need" alodine most, are the extrusions and edges of sheet material that do not have the protection of Alclad (pure aluminum)..the whole process is easy as cake and not as critical as perceived. Alodine when dry is an oxidizer, so rinse and dry all rags before disposal.
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