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Rattle Primer Issue

A

amaris

Well Known Member
I'm having hit or miss issues with primer and wanted to see what everyone thought.

Most of the pieces I bought already were alodined or primed so I've yet to need to prime large surfaces, so I'm mostly doing small pieces right now.

My process has been:

Maroon scotch w/ alumi prep, immediate wash and then acetone wipe down, then dry then prime with SEM self etch or the napa.

From the start to finish I wear gloves so not to touch it and the parts are always laid on something clean and oil free.

Most of the time it works fine, the primer dries quickly and within a day is pretty scratch resistant and fine for some of the small interior pieces that will be hidden away.

But on occasion, a small section of it will just bubble up and flake right off.

Latest was a wing rib that had to be replaced. There's about a 2" spot on it that flaked right up and the rest of it is in great shape.

It's happening maybe 25% of the time, so not always. Is it possible the parts need even longer to dry after the acetone or should I use something different? I'm in CA, so pretty much anything with a "ene" is not sold here, including MEK.

I know people have had good luck with the self etch for this type of scenario, don't want to make this about using that or 2 part.

Thanks.
 
I use lacquer thinner after roughing up and before spraying with SEM. It seems to work decently enough, if you can get that where you are. I do look carefully to ensure that it dries before I spray but I live in a high, dry area and it almost always does dry fast.

Dave
 
Acetone residue

I'm told acetone leaves a residue that isopropyl alcohol will remove.

Is rib replacement relative to priming?
 
I've been using SEM gray self-etching primer from a rattle can for the entire empennage kit, even some of the steel parts. And, have had very good results.

I just use the green Scotchbrite and clean with acetone. Then, I spray a light tac coat, wait a couple of minutes, then a 2nd coat, wait about 5-10 minutes, then a 3rd coat, while looking closely for misses and thin spots.

These are all very light coats. And, I don't spray unless I've got nice warm temps. If its 70 degrees or better, and not humid, I'll just lay the parts out in direct sunlight. If not, i'll use halogen lamps to keep the surface temps up for at least 12 hours. Small parts, I'll put in the oven on the "keep warm" setting for a couple of hours while the wife is out of the house.

I have not had any bubbling or peeling problems.

one thing I do is use brand new microfiber cloth to final wipe all parts just before spraying. Once, the acetone had flashed off, its important to wipe it with a soft dry cloth. Don't re-use cloths for the final wipe. The Acetone will pick up Sharpie ink and other contaminates and drag it across your "clean" parts.

I buy the cheap yellow microfiber cloth bundles from Costco. Once I've used them to final wipe, they become shop rags or get laundered and used for other things around the house.
 
in California

I use Maroon Scotch-Brite to clean the part with denatured alcohol, let dry, then spray with SEM, SW, or Napa self-etch primer; whichever can is closer. I've been getting good results. No bubbling or peeling as long as I let the parts fully dry.
 
All good info, thanks. I suspect maybe the acetone didn't fully dry since you guys have had luck with the same process.
 
The Acetone/MEK or most other types of chemical cleaners does leave a residue. Rubbing alcohol does not. Use the alcohol as your last chemical to come into contact with the metal part.

One other thing that is helpful is to buy some cheesecloth. You can find it in most hardware stores and even in some grocery stores. I used cheesecloth on every part that was going to get primer, proseal, paint. The cheesecloth does a very thorough job of removing any contaminants on the metal.
 
RVbySDI said:
The Acetone/MEK or most other types of chemical cleaners does leave a residue. Rubbing alcohol does not. Use the alcohol as your last chemical to come into contact with the metal part.

One other thing that is helpful is to buy some cheesecloth. You can find it in most hardware stores and even in some grocery stores. I used cheesecloth on every part that was going to get primer, proseal, paint. The cheesecloth does a very thorough job of removing any contaminants on the metal.
Click to expand...

Thanks. If alcohol will remove the oil and contaminants, is there any reason to do acetone too? I don't want to add another step in cleaning if one will work fine.
 
amaris said:
Thanks. If alcohol will remove the oil and contaminants, is there any reason to do acetone too? I don't want to add another step in cleaning if one will work fine.
Click to expand...

The contaminates in this case may simply be the soap portion of the alumaprep.

The water wash and isopropyl should work OK.

I'm wondering if you just had some moisture left over before spaying.
 
Degreasing PRIOR to scuffing...

I would recommend that a degreasing operation be performed PRIOR to scuffing... or at least scuffing wet with cleaner (MEK, acetone, etc). Otherwise you may run the risk of impregnating contaminants into the aluminum that could cause poor primer adhesion.
... and then of course your favorite final cleaning method immediately prior to priming.
My 1.5 cents
 
amaris said:
Thanks. If alcohol will remove the oil and contaminants, is there any reason to do acetone too? I don't want to add another step in cleaning if one will work fine.
Click to expand...

We use the 988 or 2027 for most every thing inside and have had very good luck with Scotch- Bright, then clean with lacquer thinner. The only thing we use Acetone for is fiber glass clean-up or thinning epoxy. The acetone will leave some trace residue on the surface. Clean white paper towels will tell you when you have the surface clean of all residue. The kind that don't fall apart. Don't touch the peace with your bear hand after you get it clean, your skin oil will become a release
agent. Hope this helps, yours, R.E.A. III #80888
 
N329JR said:
I would recommend that a degreasing operation be performed PRIOR to scuffing... or at least scuffing wet with cleaner (MEK, acetone, etc). Otherwise you may run the risk of impregnating contaminants into the aluminum that could cause poor primer adhesion.
... and then of course your favorite final cleaning method immediately prior to priming.
My 1.5 cents
Click to expand...

I've been using the scotch-brite with the alumiprep to scrub and scuff the metal. Then washing and drying and then acetone.
 
Yeah, I've had the same problem

I've had this same flaking problem maybe 5% of the time. I wish I knew what the problem was too.

My process is dawn detergent/scotch brite scrub, Metal prep/scotch brite scrub, air dry, lacquer thinner wipe down with a clean cotton rag (wearing nitrite gloves) , then SEM rattle can. I'm in the middle of the fuselage build now (slow build kits) so I have run this process many times.

The remedy always works - light scuff with scotch brite pad, lacquer thinner wipe, and re-spray. That makes me think that it is a surface containment problem, since the frequency of occurrence is pretty low maybe I just miss these areas?
 
byoung said:
I've had this same flaking problem maybe 5% of the time. I wish I knew what the problem was too.

My process is dawn detergent/scotch brite scrub, Metal prep/scotch brite scrub, air dry, lacquer thinner wipe down with a clean cotton rag (wearing nitrite gloves) , then SEM rattle can. I'm in the middle of the fuselage build now (slow build kits) so I have run this process many times.

The remedy always works - light scuff with scotch brite pad, lacquer thinner wipe, and re-spray. That makes me think that it is a surface containment problem, since the frequency of occurrence is pretty low maybe I just miss these areas?
Click to expand...

I'm suspecting it's a moisture issue or residue with acetone. I've gone back and touched up the areas with a dry scrub then wipe down, dry it and then prime and the area always turns out fine. I'm going to try alcohol and a little time with the blow dryer to see if that helps.
 
I'm told acetone removes oil, so you can't leave out the acetone step, and isopropyl alcohol removes acetone residue. This from a highly experienced composite house... for cleaning molds and for cleaning product prior to painting. They say wipe with acetone in one direction followed by wipe with isopropyl alcohol in one direction. They don't like MEK for health reasons. I don't know if MEK leaves a residue. I have used Coleman lantern fuel with no post alcohol wipe followed by etch primer, the kind you mix and spray, with no problem but I'm thinking the composite house has a better way because of their professional expertise.
 
Last edited:
Bubble

There's some sort of contaminant causing the bubbles.
Try scrubbing with Bon Ami cleanser then a thorough rinse, dry and spray.
 
SEM

SEM self etch primer is the best in my experience. Adheres very well.
I use a cleaner/degreaser sold by my local autobody
Supply store. By the way SEM or (NAPA not as good) will not prevent
Rusting on steel. Epoxy primer on steel parts or high wear areas.
 
wirejock said:
There's some sort of contaminant causing the bubbles.
Try scrubbing with Bon Ami cleanser then a thorough rinse, dry and spray.
Click to expand...

I was under the impression from reading about the alumiprep, but I thought that would also help remove any contaminants. Does it not?
 
agirard7a said:
SEM self etch primer is the best in my experience. Adheres very well.
I use a cleaner/degreaser sold by my local autobody
Supply store. By the way SEM or (NAPA not as good) will not prevent
Rusting on steel. Epoxy primer on steel parts or high wear areas.
Click to expand...

I did some tests with SEM, Napa and Sherwin and liked the SEM the best because it was cheaper than Sherwin and held up better than Napa.
 
Okay, I'll ask one more general question.

How do you guys handle big pieces like one of the wing skins? I haven't found a tub wide enough yet to fit it.
 
amaris said:
I was under the impression from reading about the alumiprep, but I thought that would also help remove any contaminants. Does it not?
Click to expand...

It's basically an acid with soap added...:)

The soapy bits/etched-off-remnants still need to be removed.
 
Rattle Primer Issue-Alodine Tank

amaris said:
Okay, I'll ask one more general question.

How do you guys handle big pieces like one of the wing skins? I haven't found a tub wide enough yet to fit it.
Click to expand...

I found the crate that the wings came in (top removed) was just about the right size. I lined the crate with poly sheet from Home Depot, made a drain in one corner, mounted it on sawhorses, and poured in the Alumiprep. Cleaned the parts, drained the Alumiprep, rinsed the tank, filled the tank with Alodine, treated the parts, rinsed them, drained the tank, and rinsed the tank.
 
I always thought Alumaprep was a "re"-conditioner, for dirty, oxidized aluminum in which the Alclad was compromised.

With new-condition Alclad aluminum, is it really necessary?
 
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