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Akutan Bandit

Member
In order that this may avoid the "endless debate" loop, I'll just post some general ideas regarding my intent to paint my airplane including some repair of very light hail damage.

I've started stripping old paint with a peroxide based stripper (Removall 220). It is my intent to get most of my old paint off due to the presence of some filiform corrosion, then to use metalprep and alodine on the skins. Based on ideas from these boards I'll then use a 2 part epoxy primer (won't mention the brand), and only then use resin and balloons to skim the hail damaged areas lightly. After blocking these I intend to shoot the top-coat, then color sand if my technique leaves any orange peel.

Am I leaving out any critical steps or making some egregious errors in my plan? I intend to do some glass work and will skim these fiber areas with a neat epoxy clear cote before shooting per DanH. I know Vic has mentioned filling with a product called Aerodynamic Dent Filler, which I considered, but would just rather not start the low-spot chasing that comes with spot repair and would rather mud the whole area with micro.

Hopefully this all sounds reasonable, although I'm open to any other input. Thanks to the boards for all the ideas.
 
Glass then topcoat ???

While applying primer and then glass/bondo/etc "might" be OK, you will generally want to put a sealer or another coat of primer/sealer over any areas that have had additional body work. Nearly all brands of paint are designed to bond with a uniform primer subcoat to give a consistant topcoat color. If you have areas that are not sealed, the topcoat "may" not appear uniform after it drys out.

You might get away with it but there just isn't any reason to do it. Assuming your basic strip and prep are OK, having a very uniform layer of primer/sealer helps insure a uniform color application.

Go to the Dupont Aviation website and pull down the product info and "systems" they recommend. You can do that for other brands as well. Best advice is start with the topcoat and use the "system" recommended for the sub coats.

You will have a lot of bucks and time in a good paint job. Don't take shortcuts with material. Follow the manufacturers directions for the whole system and you will likely end up with a nice paint job.

Just my .02

Bill S
7a almost there
 
I am in the process of preparing my plane for paint and starting to think about filling the various dings, dents, damits and doozies. Not too mention at least one bird strike.

I have the Aerodynamic Dent Filler from ACS. I am pretty sure this is good stuff. However does anyone know what surface prep is required?

I know I need to scuff and alodine but should I prime the area first and after? I thought of having my painter do the work but I can save $$ and do it myself.

Here's the repair process I am considering:

1. Sand area with 220 grit sand paper
2. Clean with MEK
3. Treat with Alodine 1200 (1000 preferable)
4a. Locally prime (Rustoleum Self-Etch)?
4b. Apply Aerodynamic Dent Filler (or Microballon/Epoxy)
5. Locally prime(Rustoleum Self-Etch)?

Also, it is my understanding that Polyester Resin should be used on aluminum and instead of Epoxy?
 
body work first

Bandit,
Do the body work after stripping and before you prime! (And do as little body work as possible). Also, I would NOT try to do body work with epoxy and micro-balloons. Use a product designed for body work such as Evercoats metal glaze. It will provide a feather edge when sanding and NO pinholes. Micro is nothing but pinholes. These body fillers are designed to adhere to raw metal and do a great job.

You'll get a better bond to the raw metal and then you can top coat the primer immediately (as designed) instead of letting it cure and "trying" to scuff sand it. Epoxy primers aren't really designed for sanding. They're designed for adhesion and anti-corrosion.


Akutan Bandit said:
In order that this may avoid the "endless debate" loop, I'll just post some general ideas regarding my intent to paint my airplane including some repair of very light hail damage.

I've started stripping old paint with a peroxide based stripper (Removall 220). It is my intent to get most of my old paint off due to the presence of some filiform corrosion, then to use metalprep and alodine on the skins. Based on ideas from these boards I'll then use a 2 part epoxy primer (won't mention the brand), and only then use resin and balloons to skim the hail damaged areas lightly. After blocking these I intend to shoot the top-coat, then color sand if my technique leaves any orange peel.

Am I leaving out any critical steps or making some egregious errors in my plan? I intend to do some glass work and will skim these fiber areas with a neat epoxy clear cote before shooting per DanH. I know Vic has mentioned filling with a product called Aerodynamic Dent Filler, which I considered, but would just rather not start the low-spot chasing that comes with spot repair and would rather mud the whole area with micro.

Hopefully this all sounds reasonable, although I'm open to any other input. Thanks to the boards for all the ideas.
Click to expand...
 
I would prime the aircraft first then do the body work. That makes it really easy to spot the little hail dents. I use a drop light to highlight the dings and mark them with a pencil. Each little ding then gets sanded with 80 grit sand paper by hand. For filler I use Evercoat in two applications, sanding in between. When your done you will have little rings of bare metal around your filler spots. Retreat these with alodine then prime with epoxy primer. Go over that primer with two coats of high build primer. AKZO Awl-Quick or PPG K-36 are my favorites here. Guide coat and sand those spots the next day. Hope this helps.
 
I know a little bit about this

After you prepare the metal, prime with epoxy primer first, then do the body work. Spot prime the filler with a good surfacer primer like PPG K-36. Level with wet or dry 400 and a flexible rubber block. Do not try to level sand with your fingers. Use the block. Touch up the epoxy primer where you sanded to bare metal, then apply top coat.

There are light weight bondo like fillers out there that are much easier to sand than epoxy and micro balloons. You don't have to build up a lot of paint thickness. Thin coat of epoxy primer, spot just the filler with the K-36, then prepare for top coat.
 
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Usually...

dedgemon said:
..... These body fillers are designed to adhere to raw metal and do a great job.
.....
Click to expand...

...these fillers you mention are designed for use on steel auto bodies, not aircraft aluminum. Just check out the grit your auto body guy uses on his grinders...:)

My painter did an epoxy coat, and then bodywork, just as the others mentioned. Doing it this way stops you from accidentally sanding away the aluminum - as soon as metal shows through the epoxy, stop sanding. It doesn't take a lot of sanding with coarse paper to make that 0.025 (or thinner) skin measurably thinner and weaker.
 
Wow, thanks for all the input.

I've put waayyyy too much time into this so far. Based on a ton of reading and the general lack of info on filling over thin aluminum my approach devolved into a series of experiments.

Initially I acid etched the bare aluminum, neutralized with soap and water, then applied commercial micro (superfil) to the bare clean metal. After much reading I decided to do my bodywork over an epoxy primer, so I picked up a high quality zinc chromate primer from SPI. At this point I was applying the epoxy primer to bare metal, then applying bodywork in the form of both superfil and homemade micro (balloons plus cabosil), then applying another layer of epoxy primer to encapsulate the bodywork. Finally I tried, and this only on the smallest dings, using a polyester based filler (Rage Gold Pro) over the epoxy and then covering that with epoxy. I was reluctant to use the polyesters so only tried a few small spots with this.

General observations are many but here are a few. The irony of these fillers is that the stickiest fillers are the toughest to sand. In the places where you need the best adhesion, like over the thinnest skins with the most flex, you end up trying to sand and feather a rock-hard mass in a very difficult area. It is well established that epoxy fillers adhere best, especially over an epoxy primer, but both Superfil and especially homemade micro is a bitch to sand when the substrate is flexing. Additionally you need to skim them with neat epoxy because they pinhole like crazy, so then you need to sand again. Polyester fillers like the Rage don't chemically adhere to epoxy primers and so can pop off when applied to a flexing substrate. Of course they are super easy to sand and can be painted over in about 30 minutes from application, plus I found very few pinholes with the high quality auto polyesters.

In summary my system now is to use an epoxy primer, then fill with a minimum of epoxy filler, sand, skim with neat epoxy, sand, apply epoxy primer again, and then skim a very very thin layer of Rage Pro over only if there are still tiny nicks or pinholes. Then I apply 2k primer. Your basic nightmare but it works. Thanks for all the input.
 
My 2 cents go with the fill the metal, and prime last crowd.

Evercoat 415 is made to adhere to metal, including alum, and I can swear to the fact it does so with a vengeance.

If you prime, then fill over the primer, the filler is dependent on the primer for adhesion.
 
For hail and quite a few other dents, have you considered one of the dentless repair guys?

Years ago, when I had my Piper Tomahawk, I had a guy come out and remove some hail dents. He had never worked on aluminum before and didn?t know what to expect, so I let him massage a few of the dents out. He was shocked and relieved how easily his tools worked the soft aluminum. So much so, that he offered me a big discount if I let him do the whole plane.
 
Mike I think the reason for the underlying epoxy primer is both corrosion resistance plus a moisture-resistant encapsulation. Most polyester fillers are verboten in the marine world because they are somewhat hydrophilic. By surrounding the filler with the epoxy primer you prevent that I think. I wish I'd seen the Evercoat sooner and would be willing to try it especially in some very thin applications and for pinholes. The epoxy primer I'm using is well known for being very high quality and also chromate rich.

John I may have to go that route on the wings. My patience has been spent on the fuselage and tail, which are looking good but just killed me on time, and the wing skins may have to wait. I'm in no mood to try filling those small dents over such thin aluminum, so I'll at least call one of the dent repair guys and see what they say.
 
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