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Priming 2 different materials

jferraro17

Opulence, I has it...
So, I've reached the point with the emp tips that I'm happy with the finish--at least I think I am.

I would like to coat these areas with primer since a final paint job is years down the road. Any suggestions on what to use? My concern is, the combination of fiberglass and aluminum in the areas that need to be coated. I'm pretty sure I can't use the self-etching rattle cans I've been using throughout the build for parts.

Thanks for any advice.

Joe
 
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I'm also at this point and dont have an answer yet how I'm going to do it so I'll be interested to see what the concensus is?
 
I am "all ears" on this one too. My plan was to use regular (non-etching) primer on the fiberglass. However, I have a couple cans of self-etching left that I wouldn't mind using up.
 
If it was me, I'd use an epoxy primer like PPG DP40 or similar. Don't go wild with the amount of coverage, because down the road you will have to scuff it all with red scotchbright and give it another DP40 coat prior to the finish coats.

Most epoxy primers have only a day to a week of "open" time before the above requirement kicks in. When the primer coat is too old, the top coats don't chemically bond to it, and peeling may happen.
 
Epoxy primer on both alum and fiberglass? Acid etch alum first?

What about filler primer for the tips? Would that go on over the epoxy primer?

I don't like the idea of acid etch sitting in between built up layers, so I'd reserve it for individual parts. Built up parts I'd carefully solvent wipe and then scotchbright etch. If the parts are already alodined, solvent wipe and shoot primer.

I don't like the idea of etch primer on fiberglass, though some mfg's may be ok with it.

Fiberglass: Fill pinholes first (resin wipe or wonderfil, or ...), then epoxy prime, them filler primer as needed. If you're going to give it a full coat of urethane filler primer, and not sand through it, then no need for the epoxy primer. The main advantage to a epoxy primer under a filler primer is that you immediately see when you've sanded through, and the epoxy is a bit tougher to sand through.

PPG's optimum plan for aluminum is a thin coat of acid etch, followed by a coat of epoxy primer. Many of their topcoats are not recommended for direct application over DX1791 (their chromate based etch primer). The DX1791 largely replaces alodining by providing some chromate based corrosion protection. Yup, it turns the metal a nice light gold color. If you don't need the extra bit of corrosion protection, epoxy straight to prepped aluminum is fine.
People have been successful shooting PPG Concept straight over DX1791, but when in doubt, follow the p-sheets, that's what I say.
 
This is a related question to this thread as I am fitting my elevator tips right now too. I am using West systems epoxy and 410 micro to fair the surfaces. after pop riveting the tip on I taped the seam with .007 2 inch wide tape then mixed the 410 filler and faired the surfaces. I am satisfied with the job except for priming then using a little fast build primer to finish the job. West systems calls for a barrier coat of just mixed resin rolled on and tipped off after the fairing work is done. Can I replace this step with PPG DP-40 epoxy and then go over that with the fast build primer. I'm thinking the rolled on epoxy will be much harder to get back smooth. Thanks
 
Ted is spot on with the PPG suggestions... I would only add that we had PPG do some testing for us a few years ago and they determined that a layer of DP48LF reduced as a sealer would penetrate the pinholes and scratches on a composite part a bit better than a filler primer, thus providing a slightly better surface for the thicker products to grip. Be sure to use the DP401LF hardner, by the way.

On an RV-10 fuselage, for instance, we'll carefully apply DX1791 to the metal surfaces, then coat both metal and fiberglass with DP48LF, then continue on with whatever filler primer is necessary to get the fiberglass properly prepared for topcoats.

Our background is mostly Lancair work, and we have found that the typical RV project needs a whole lot more TLC to the fiberglass areas than the metal... ;-) But I suppose that comes from experience, correct?

As for the DP vs. epoxy issue over the West filler, you should be OK with this substitution. As a rule, I would do a test coupon first to confirm this, but I have never had a problem with West/PPG epoxy combinations.

Brad Simmons
Airframes Inc.
Milan, TN
[email protected]
 
Hi guys,

I have been thinking of a right up on my finishing technique. I will try to keep this short but may fail at that.

In the following I will try to explain what I have learned in the last 25 years of painting. I do not want you to think that I am an expert for I will never make that claim. I am just going to explain what I will be doing and why.

Started painting my cars at 14. I would buy them fix, drive and then sell. I have had over 50 cars so far. Other than sanding and spraying technique nothing notable here. In the winter of 2007 I started a powder coating company. I started doing stunt bikes. They are mostly made of aluminum. To keep it short I will just say that for my first two bikes the powder coating did not stick. I had to find out why.

What I have learned

Oil will find its way onto your plane from every ware. I.e. your drill and rivet gun if you oil them or just from the oil in your hand. Do not use solvents ( lacquer thinners ). They do remove the oils but will leave there own contaminants.

My procedure for aluminum

I ware surgical gloves to protect the plane from the oil in my hands (the non aloe type).

1) wash- I use Dawn dish washing soap (no aloe or fragrance). Rinse let dry.

2) scuff surface usually with 3M scuff pad or 360 grit sand paper.

3) wash again just like step 1. This time it does not need to dry I proceed to step 4

4) condition with Bulk Chemicals Bulk Kleen 690. This is a non corrosive acid wash. Rinse and rise again. No need to dry

5) Pretreatment of surface with Bulk Chemicals E-Clips 2101 RTU. This is an adhesion promoter. This is sprayed on and left to dry.

6) apply a two part self etching primer (from a quality company).

7) apply an epoxy primer. There is a window that this can be recoated in. after that window it becomes to hard to scuff for adhesion. This window is outlined by the primer manufacturer.

8) apply paint. This could be a conversation in its self.

My procedures for fiberglass

The wash is different I use a 50/50 mix of Windex and rubbing alcohol to spray and wipe.
Fiberglass likes moisture so I will not wash with water. The 50/50 mix will clean and degrease. Then an epoxy primer followed by a high build primer. But the primers will go on after the west system fillers and sanding. I will be making all of my own fiberglass with exception of wheel pants. Hopefully I will not need fillers.

Please note that all of my primers are over reduced. I do not want high build and the added weight.

I will be doing this to my wings but I will not be painting right away. I will put on a light coat of2K primer over the epoxy primer. Then when I am ready to paint I will sand most of this off and then apply paint.



Also note that for the washing stage the soaps and chemicals like it better warm. The Bulk Kleen 690 works best @ 140 degrees. This is hard to do so I will turn the shop up to 80-85 and use hot water for every thing. I also force dry every thing.

Sorry if this got a little long. But this could be even longer.

Let me know if this helps or you would like to talk more in depth.
 
Herricane,

I couldn't agree more... in other words, clean, then clean again. I think a lot of folks don't realize how diligent you have to be about cleaning and degreasing. Or how a seemingly insignfigant thing like putting oil in an air drill or using WD-40 to lube the shop door hinges can create a painting disaster...

I'm curious about the Windex... you use this for the ammonia or why?

Brad
 
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