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Go Back   VAF Forums > The Never Ending Debate Section > Primers
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  #31  
Old 07-09-2022, 11:29 PM
idubrov idubrov is offline
 
Join Date: Mar 2021
Location: San Antonio, TX
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Quote:
Originally Posted by skelrad View Post
True, but not sure it really matters.
I agree. I just don't have any extensive experience with primers or paint, so I don't know what is normal and what is not.

I am at the empennage stage, so at this point I mostly care that it does not fall off the parts after a few years
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  #32  
Old 08-03-2022, 03:05 PM
idubrov idubrov is offline
 
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I was curious how much weight do I add, so I weighted couple of random parts I sprayed with EkoPoxy. Two ribs and a small spar from the elevator, all fully covered.

The total weight increase was ~3%, which seems to be not too great. I saw mentions of increase more than 1.5% as a "fail" in some A&P school.

Will re-check my application with the gauge and see if I can get a thinner coverage that still looks okay (I use 1.8mm nozzle, so maybe switch to 1.4mm and thin the primer with water a bit?..).
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  #33  
Old 08-03-2022, 04:06 PM
David Paule David Paule is offline
 
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I bet that rule of thumb was from a long time ago, when many coatings cured by evaporating solvents. Just a guess, I ain't a chemist or a painter at all. Not even close.

A two-part paint will have considerably less reduction. Typically, the proper thickness is based upon film thickness, cured.

Dave
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  #34  
Old 08-24-2022, 12:08 PM
idubrov idubrov is offline
 
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To avoid creating a separate topic, any reports on using Stewart Systems EkoPoxy without their EkoEtch etching?

How would I know that I get enough primer bonding? Is scratch / peel test few days later enough or is there still a risk that it will peel off, say, after being exposed to hot temperature / big temperature difference?

I am considering to switch to something non-corrosive, potentially PreKote. The main issue with etching for me is that when I work with small parts, it gets tedious to track the time (and keeping etching longer than necessary seems to leave corrosion on the parts) and also it's easy to get splashes on other parts being prepared (which also leaves corrosion dots on them).

With PreKote, I would imagine, I can spray / scuff as many parts as I want (keeping them wet), then wash everything at once.

This is primarily for an internal application.
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  #35  
Old 08-24-2022, 12:55 PM
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wirejock wirejock is offline
 
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Location: Estes Park, CO
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I test cured paints using Gorilla tape.
Once fully cured, apply a strip. Rub it down. Leave it overnight. Rip it off.

I weighed a lot of parts over the build and typically saw about 1% weight increase.
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  #36  
Old 08-24-2022, 01:05 PM
David Paule David Paule is offline
 
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Quote:
Originally Posted by idubrov View Post
To avoid creating a separate topic, any reports on using Stewart Systems EkoPoxy without their EkoEtch etching?...
I didn't etch on the interior of my RV-3B, where I used EkoPoxy. It's been more than a year, maybe two years, and I've been working in the area since. It's held up well. I used Scotchbrite maroon followed (and preceded) by either lacquer thinner or isopropyl alcohol, and a small touch-up spray gun to apply it. I'm satisfied.

Dave
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  #37  
Old 08-24-2022, 01:19 PM
skelrad skelrad is offline
 
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Quote:
Originally Posted by David Paule View Post
I didn't etch on the interior of my RV-3B, where I used EkoPoxy. It's been more than a year, maybe two years, and I've been working in the area since. It's held up well. I used Scotchbrite maroon followed (and preceded) by either lacquer thinner or isopropyl alcohol, and a small touch-up spray gun to apply it. I'm satisfied.

Dave
Same. I used to acid etch everything. Then I did some side by side tests of etch vs scotch brite scuffing. Found zero difference in adhesion. So now I just scuff and wipe things off with acetone, then prime. It's probably a wash in terms of time required, so really just preference of the materials you want to work with. Etch and water rinse or scuff and wipe with a cleaner.
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