Rattle Primer Issue
 

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.

John, no, I damaged the rib drilling out the tooling hole for my pitot grommet so had to replace it.

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.

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.