Paint Prep - Carbon Fiber Parts

[jmorrical]

I back in the paint booth to finish small parts. Do I lightly scuff and prime carbon fiber engine cowlings and cargo bay door before paint? Or just scuff and paint?

Somewhere I read that CubCrafters was not priming carbon fiber any more. I'm looking for best practice.

[Pete D]

Hi Jim,

Somewhat correct. No, the composite parts do not get “primed” with the primer used elsewhere, however a PPG DP50LF/DP402LF Epoxy primer is used to seal the composite parts. This also helps even out the color so the composites match the rest of the airplane after the color coats are sprayed. (The sealer is a neutral grey color)

[jmorrical]

Pete,

I read painter blogs from time to time to learn more about it. Some painters admit trying to explain the difference between a primer and a sealer is not easy. You say the carbon fiber is not 'primed' but yet....a PPG DP50LF/DP402LF Epoxy primer is used to seal the parts.

Ok, I give up. Ha!

I just need to have faith that using a primer not to prime will seal the surface. I will try not to get locked up on this and just smile in the paint booth thinking about it.

[Daveembry]

Hi Jim,

Somewhat correct. No, the composite parts do not get “primed” with the primer used elsewhere, however a PPG DP50LF/DP402LF Epoxy primer is used to seal the composite parts. This also helps even out the color so the composites match the rest of the airplane after the color coats are sprayed. (The sealer is a neutral grey color)

huh? Which one is correct?

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[aflyer]

Did you get a back-channel answer to this?

Seems rather important. I am at this stage now.

John

[Daveembry]

Crickets. Here is a link to a post I did on this in my Building the EX3 - Tips & Hints. I include links to the PPG Spec Sheets and list what is recommended by PPG. You can see they do say to use a different primer for the composite materials. I inquired into this when I first started using it and you can see that I was told they did NOT prime/seal the composites as called for by PPG but it appears now maybe they do????

I have painted 3 planes now with it and did NOT prime/seal the composites since they said they did not. My local PPG guy here said most of his customers did NOT use that primer on composites either if they were smooth.

So that's all I've got. Check it out here:

http://forum.cubcrafters.com/showthr...ll=1#post25050

Did you get a back-channel answer to this?

Seems rather important. I am at this stage now.

John

[Pete D]

Sorry for the confusion, when Dave asked early on about the primer question on composites our paint shop told me no, they do not prime them.

Since then I have been told that they now seal them, with the PPG DP50LF/DP402LF Epoxy primer. Reason is twofold, it does help cover things up so the composite weave doesn't show through, but also covers up the darker gel coat color to get a better paint match to the other surfaces on the airplane. It isn't critical but should make it easier to get a better finish and match particularly if painting lighter colors.

I hope that explanation makes sense.

[aflyer]

Thanks very much!

My friend the retired airplane painter (a very knowledgeable and experienced guy) was very insistent that I prime everything.

For aluminum, he said I have to acid-etch, alodine, and then prime before paint. This is the way he painted my RV8 which came out beautifully. I take it CC just uses an etching primer without the first two steps? Or is it just scuff and paint?

John

[Daveembry]

That’s why going with the manufacturers recommendations are probably the best way to go. Did you download and read the PPG Data Sheets in the link I gave you. Explains everything as they recommend it in detail. Things are changing fast and manufacturers recommendations probably supersede the “Old retired painter”. 😉

Look at the data sheet for the sealer recommended. It explains the process. No etching or primers allowed before application. It’s “direct to metal” or for use over gel coated surfaces.

Thanks very much!

My friend the retired airplane painter (a very knowledgeable and experienced guy) was very insistent that I prime everything.

For aluminum, he said I have to acid-etch, alodine, and then prime before paint. This is the way he painted my RV8 which came out beautifully. I take it CC just uses an etching primer without the first two steps? Or is it just scuff and paint?

John

[aflyer]

Dave, I appreciate all the work you have done to detail your building methods.

I have read through the data sheets extensively, and try to listen to all the experts, you, the guys in the local paint store, and the old painter who just retired 6 months ago. I have spent hours reading the PPG stuff.

In the FDGH data sheet, one statement says "Performance Comment: Wash and Etch primers must be sealed before applying topcoat for optimum performance". The recommended 3960 is an etch primer. I haven't heard any mention of that from you or CC or any of my other experts.

I am feeling some frustration this morning after a disaster yesterday painting my struts. I'm still looking into the cause, but it may be that I didn't seal the primer, there is some incompatibility there. I will try to call PPG when they get to work.

Thanks, John