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Preparation for Priming

ravenstar

Well Known Member
Hi everyone, after lurking for months, I'm hoping to begin my own RV-12is project very soon, and I've got many questions. To get the ball rolling, I'm trying to arrive at a decision on interior priming that I can live without second guessing myself for years. Before I start my build I thought I'd experiment with some primers on the practice toolbox kit I've built.

I'm very conflicted: I tend to feel like others who don't want to damage the protection of the alclad surface to add a different kind of protection (not to mention all the effort to thoroughly rough up each piece -- did I hear 200 hrs added build time?), but I also like the look of the primed surface and the possible corrosion benefits. So I tried something I haven't seen discussed here yet: I cleaned one surface with Dove soap and when that failed to prevent the water from beading, I used a cheap supermarket clone of Windex since it's what I had hanging around to clean the surface then one more wash with detergent. Then I primed it with SEM primer without doing the usual sanding.

I guess this was the first time I've used a decent primer as I was stunned by the toughness of the coating. 24 hours after two passes 10 minutes apart, rubbing the surface with a dull edge of a piece of metal didn't leave any noticeable mark.

So now I'm wondering just how important scuffing up the surface is to getting a good bond? Seems like cleaning was most important. And what about the simple household cleaner I used in the prep? I wasn't expecting it to be so simple or effective, so I started looking around and couldn't find any reliable information on whether it would have an adverse affect on the metal or paint.

Any thoughts about this prep process? I'd rather not prime than prime in a way that damages the surface, or is just wasted effort.

Many thanks!
 
Surface prep

My opinion. Worth $.02

Search for Aluminum Oxide

I am in the full prep ball park.

A light scuff and clean shouldn't damage the Alclad. All you're trying to do is rough the surface and remove aluminum oxide. Water break free surface is the goal. Hydrophillic surface.
Back to Aluminum Oxide. That's the thin layer that effects adhesion. Its hydrophobic. Water beads.
Lots of opinions.
Most cleaning products won't remove it unless they have an acid. I prefer Bon Ami and scotchbrite. Clean and scuff at the same time. Dry. Shoot.

The other method is chemical removal. Alumiprep with scotchbrite will remove it and scuff the surface. I also use it on some parts.

SEM is self etch so it's going to chemically etch the surface to promote adhesion. Lots of builders love the stuff. No personal experience.

There are some products you wouldn't use without a very thorough rinse. Bleach for instance. Some window cleaners have ammonia or vinegar. Test.

Test your paint. Shoot several tokens. One control with no cleaning. The rest cleaned or scuffed or both with various methods. Cure. Appy a section of black Gorilla tape. Leave it a day or two then rip it off. Go with whichever works best.
 
My $0.01

On my empennage I probably took it too far and primed all internal surfaces.

Like you, new to aluminum construction procedures. People I respect very much advised to not prime and maybe they are correct.

However, this is my future family member in the form of an RV10!

My procedure:

Prep as many parts as possible at once. Turn on the best garage music you can find. Debur and scotchbrite like a madman. I scrubbed every surface of everything.

Then, on a bright sunshiny day, set up multiple picnic tables on the driveway. Lay out all your parts and spray alumiprep on all of them. Have your paint process ready to go.

A quick scrub with scotchbrite and acid prep (alumiprep) and GLOVES. After about 15 minutes rinse thoroughly, let dry in the sun.

I used AKZO two-part epoxy. Mix it and give it the 30 minutes (?). Blow dry all your little parts just to make sure you've removed all water residue.

Move parts (with gloves to prevent oil from contaminating the surfaces) to your "paint booth".

I invested in a Hobby Air hood and air supply. Don your disposable cover-alls and gloves and have fun painting !!

AKZO: applies easily, dries fast, provides a super durable finish that looks good - if you like ugly green.

Bottom line: the process was not bad at all. Probably only four mornings spent on painting for the entire empennage.

Reach out any time to talk. Also, I am open to any and all advice.

Andy
 
Process

On my empennage I probably took it too far and primed all internal surfaces.

Like you, new to aluminum construction procedures. People I respect very much advised to not prime and maybe they are correct.

However, this is my future family member in the form of an RV10!

My procedure:

Prep as many parts as possible at once. Turn on the best garage music you can find. Debur and scotchbrite like a madman. I scrubbed every surface of everything.

Then, on a bright sunshiny day, set up multiple picnic tables on the driveway. Lay out all your parts and spray alumiprep on all of them. Have your paint process ready to go.

A quick scrub with scotchbrite and acid prep (alumiprep) and GLOVES. After about 15 minutes rinse thoroughly, let dry in the sun.

I used AKZO two-part epoxy. Mix it and give it the 30 minutes (?). Blow dry all your little parts just to make sure you've removed all water residue.

Move parts (with gloves to prevent oil from contaminating the surfaces) to your "paint booth".

I invested in a Hobby Air hood and air supply. Don your disposable cover-alls and gloves and have fun painting !!

AKZO: applies easily, dries fast, provides a super durable finish that looks good - if you like ugly green.

Bottom line: the process was not bad at all. Probably only four mornings spent on painting for the entire empennage.

Reach out any time to talk. Also, I am open to any and all advice.

Andy

That is an excellent process. Should serve you well. Love my Hobby Air.
Only thing I would add is when you move on to interior color, wipe surfaces with a tack cloth right before pulling the trigger. The tack cloth will grab any dust or particles.
 
If you don’t want to use an acid etch you can wash once with soap and water followed by washing two times with AKZO Metaflex SP 1050. Metaflex is a water based adhesion promoter. It works very well. AKZO 10P2111 primer goes good with that.
 
My opinion. Worth $.02

SEM is self etch so it's going to chemically etch the surface to promote adhesion. Lots of builders love the stuff. No personal experience.

There are some products you wouldn't use without a very thorough rinse. Bleach for instance. Some window cleaners have ammonia or vinegar. Test.

Test your paint. Shoot several tokens. One control with no cleaning. The rest cleaned or scuffed or both with various methods. Cure. Appy a section of black Gorilla tape. Leave it a day or two then rip it off. Go with whichever works best.

This I think is where I'm going for simplicity and minimal toxicity. My first experiment with the SEM was very positive. That stuff adheres better and is tougher than any paint I've used on any surface. But I don't have any experience comparing it to the other high end epoxy primers and paints. I've done epoxy/fiberglass work before and I'm a big fan of it in general. But I just don't see myself going through all the prep and cleanup work for all the parts that I will want to prime. This is a project I'll likely do in many frequent short work sessions. Self-etching seems the best fit for me, if it works.

To your point, I know the cleaner I used for my first test had ammonia in it, which I don't think I'd want to use on an aircraft part, though I haven't found anything definitive on that matter. I didn't try SEM without that cleaning, though, so I'll try the test you suggest along with a minimally prepped surface just to see what happens, thanks.

To everyone who replied, thanks. You've also got me reconsidering your approach. Perhaps I have the wrong impression of the effort involved in the preparation steps, so I'm going to go back and reread information the approaches you've suggested. I do want a high quality product, but it seems in the case of interior priming, it's very hard to sort out what different levels of quality mean.
 
Other camp

I am in the other camp.
I deburr all the parts, scrub with scotchbrite, wipe with acetone and shot the primer. No harsh chemicals to deal with except acetone and primer. Has worked well with very good adhesion. Same prep for painted parts. I am using shermin williams pg primer like the factory. Paint on key interior parts is jetflex, the good stuff. Never had a paint adhesion problem and very staisfied with ease of application and results.

My exterior paint will be a professional job with all the trimmings; i wont get near all those chemicals. Even with me applying the primer i use good protective mask and googles. Never breath the fumes of the primer chems, really bad for you. But the other steps are done in the open air. The mask goes on before the first can of primer chemicals is opened, and comes off when the last can is sealed and all the stuff is cleaned up and disposed of.

I did not use the alum prep, or any other surface treatment prior to prime, only acetone wipe.
 
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I use Alimiprep for everything. Apply it with scotchbrite pads, rinse off and look for the clean water sheeting.

Next, I bought a gallon of Prekote. We'll see how that goes. Going to do some more research, but it sounds like Prekote does NOT chemically etch the metal, so might be doing some form of acid etch before Prekote. Likely be weak mix of Alumiprep, water rinse, then Prekote, air dry, spray primer.
 
Soap and water wash with Dawn, then rinse. Spray with Prekote and scuff the surface with maroon Scotchbright, then final rinse and dry with clean wipes.

The Prekote directions say to do it twice. The second time scuff it 90 degrees to the first direction so you get a cross hatch scuff. I admit that sometimes I only do a single pass and it doesn't seem to affect the results.

I don't use Alumiprep or Alodine (Bonderite) because the runoff is considered toxic waste and needs to be captured and disposed of properly.

I use Akzo two-part epoxy green primer and the stuff is tough as nails if you do the surface prep correctly. I'm considering switching to Ekoprime though.
 
The Prekote directions say to do it twice. The second time scuff it 90 degrees to the first direction so you get a cross hatch scuff. I admit that sometimes I only do a single pass and it doesn't seem to affect the results.

What happens if you scuff in circles?
 
I've decided to use Stewart Systems. I wanted to get their recommendation, so emailed them about how to use the products:

We recommend etching the aluminum by spraying it lightly with EkoEtch mixed with water and then rubbing it for a few minutes with Scotch-Brite. Then rinse with water. It is critical to do this on any surface that will be painted. On interior parts if you were doing primer only corrosion protection you could just clean it with EkoClean and spray it with EkoPrime. It will not get as good of adhesion, but on an internal surface that will not be disturbed it should not be an issue. It will provide good corrosion protection.

I then asked how important it was to use the EkoClean product first or if I can get away with just using EkoEtch (I want an etch for durability, so not going to just clean and shoot primer like their first email said was okay for internal surfaces):

In reality, in most cases it makes little difference. The etch contains detergents and will clean the surface while etching. If the metal is new or reasonably clean, EkoClean is not really necessary, but can’t hurt either. If the metal is dirty, I would clean it first with EkoClean. No real reason to clean after with EkoClean unless you are working on an assembly and working hard to get it all out of the hidden places. EkoClean can help with that. Getting etch all rinsed out is very important. As long as the metal will sheet water off without beading up you have a good etch job.


So from what I gather, the bottom line is just get it clean one way or the other. If it's clean and you shoot primer, you're probably fine (on internal surfaces). If you etch and shoot primer, you're fine. I'm just planning on use their EkoEtch and doing a very light, quick scuff with Scotchbrite to clean and scuff at the same time.
 
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