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Cowl painting question

Charles in SC

Well Known Member
I have the fiberglass parts about ready to paint. This paint is just to protect the material until I have 40 hours flown off and can take the plane to get a real paint job. I have read that the final paint shop will probably remove whatever paint I apply to get through the 40 hours. What are some paint s that I should consider? I was thinking Stewart System rather than a 2 part epoxy because it would be easier to sand off. Any input will be appreciated.
Thanks in advance!
 
Any minor flying damage to the fiberglass would be trivial to repair vs removing all that paint. I say leave it as-is and fly it like you stole .. er .. built it! :D
 
Any minor flying damage to the fiberglass would be trivial to repair vs removing all that paint. I say leave it as-is and fly it like you stole .. er .. built it! :D

Maybe, but I would be more concerned about oil/grease soaking into the fiberglass surface than minor damage.

Check with your painter but two local guys told me to use a two-part epoxy and they will sand it (maybe all off, maybe just scuff it) before they painted.

Any non-epoxy primer would probably give a more porous and absorbent surface.
 
Flew for two years with Stewart ekoprime only on the fiberglass. Plane is finally at paint shop now, and it was all easily removed.

Chris
 
I painted the inside with a two part primer and covered it with reflective heat shield from Vans - to protect from oil/fuel. The exterior is still bare after 150 hours and a little over a year.
 
Don?t forget fiberglass and ultraviolet light do not mix well. Put something on it.

This is what I do for flying before final paint:
- Prep all fiberglass to fill pinholes per the Van?s instruction.
- White two part epoxy primer on the inside of the cowl (e.g. PPG DP48LF). Two coats. Do this before first engine start.
- Van?s stick on aluminum heat shield on the inside of the cowl in the obvious places (check for discolor after the first few flights and add as needed).
- One coat of PPG epoxy primer on outside of the cowl and all fiberglass.
- One coat PPG single stage paint in your choice of color on top of the primer. I find a medium blue goes well with the rest of the plane in bare aluminum.

Reasons:
- Anything you can do to prep the glass will be appreciated by your painter (especially if that painter is you). He might even drop the price a little as he?ll see the PITA fiberglass prep is well started. The primer and top coat paint will also give the paint guy material to block sand - that will only improve the final product.
- Even though you plan on painting right after the flight test program, odds are you will be flying like this for some time. The simple extra step of adding a coat of color on the fiberglass will make it look worlds better.

Carl
 
Maybe, but I would be more concerned about oil/grease soaking into the fiberglass surface than minor damage.

Check with your painter but two local guys told me to use a two-part epoxy and they will sand it (maybe all off, maybe just scuff it) before they painted.

Any non-epoxy primer would probably give a more porous and absorbent surface.

+1

Most non-two part (i.e. catalyzed) paint will be porous and won't help with liquid contaminant intrusion of the fiberglass. Go to the local paint store and get a lower cost epoxy primer and spray two coats on.

Also, some airborne contaminants can be just as much of a problem for paint adhesion as oil.

Larry
 
Don?t forget fiberglass and ultraviolet light do not mix well. Put something on it.

This is what I do for flying before final paint:
- Prep all fiberglass to fill pinholes per the Van?s instruction.
- White two part epoxy primer on the inside of the cowl (e.g. PPG DP48LF). Two coats. Do this before first engine start.
- Van?s stick on aluminum heat shield on the inside of the cowl in the obvious places (check for discolor after the first few flights and add as needed).
- One coat of PPG epoxy primer on outside of the cowl and all fiberglass.
- One coat PPG single stage paint in your choice of color on top of the primer. I find a medium blue goes well with the rest of the plane in bare aluminum.

...........

Carl

Exactly what I did, except for the last step of a color coat.

I thought the flat white primer look in the glass parts was OK. :)

I used Kirker epoxy primer in white and painted both the inside and outside of the cowl as you did -

https://www.autobodytoolmart.com/kirker-enduro-prime-epoxy-primer-p-12620.aspx
 
Don?t forget fiberglass and ultraviolet light do not mix well. Put something on it.


Carl

Just to be a picky PITA, it is not the fiberglass that breaks down, it is the epoxy resin that holds it together. I would use any good 2 part acrylic urethane primer. It is high quality, compatible with any paint, sticks like crazy, cures quickly and it will seal and protect the cowling. Being catalized it will be impervious to most things - thinners etc. They make it high build so you can fill the weave and other imperfections.
 
Just to be a picky PITA, it is not the fiberglass that breaks down, it is the epoxy resin that holds it together. I would use any good 2 part acrylic urethane primer. It is high quality, compatible with any paint, sticks like crazy, cures quickly and it will seal and protect the cowling. Being catalized it will be impervious to most things - thinners etc. They make it high build so you can fill the weave and other imperfections.

Most 2K high build primers (even urethane) are porous. Base metals and F/G should be coated with an epoxy primer for protection. The purpose of the 2k primer is for filling and flattening, not protection. Standard 2 k primer, once covered with a 2k clear coat will provide protection, but it is the clear coat protecting. The general rule is that if it sands easily it is porous.

Larry
 
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+1

SPI is all that I use. I'm is very high quality and affordable. You won't find better support for amateurs.

I have suffered from "Swiss cheese effect" from time to time with SPI's epoxy. There are several references to it in their forum. Effectively, it looks like a mass of fish eyes. Regardless of my efforts to eliminate it through longer induction time and thinner coats, I have not been able to consistently eliminate the problem.
 
I have suffered from "Swiss cheese effect" from time to time with SPI's epoxy. There are several references to it in their forum. Effectively, it looks like a mass of fish eyes. Regardless of my efforts to eliminate it through longer induction time and thinner coats, I have not been able to consistently eliminate the problem.

Give Barry a call. He is the owner and the tech support number they give is his cell. He is VERY experienced and will help you through any issues. Tell him Larry from Chicago told you to call. He has helped me immensely. I have experienced this a couple of times (always limited to small areas and never the whole panel sprayed), but fisheyes are almost universally due to contamination (silicone is highest on the list) and will impact most all paints, though some handle it better than others. silicone is viciously invasive stuff and can also get airborne. There is a reason that paint shops work so hard to keep anything with silicone at least 100 yards from their shop. Try walking into a body shop with a bottle of Armor All and see how long it takes for someone to tackle you.

As an experiment, when you get fisheyes, shoot another coat. If they re-appear on the second coat in the same spots it is silicone. The silicone molecules rise to the top of the liquid paint and will affect each subsequent coat. It is insidious this way, as it can't really be covered up. It needs to be removed.

In my experience, the epoxy is most prone to showing the effects of the contamination. I feel this is because it is the first layer to go on the contaminated panel and the silicone is easier to remove from a freshly painted surface, so it is not a common to see it on the next layer.

You need to really work to get silicone off a bare, sanded panel. A few light wipes with wax and grease remover won't get it done. Typically you don't know it is there until the fisheyes show up and therefore don't take the extra effort to remove it, which is why you see it.

Good luck,

Larry
 
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I'm just now painting the interior or my cowl, so this post captured my interest. Whilst I don't deny that silicone may be a beast when it comes to fisheye problems, I for years suffered from fish eye issues when priming (both with water borne and traditional paints), and was told by local paint shops here it was silicone, but that appears to not be the case. The root cause ended up being moisture. The way I resolved this was running the compressor air through 8ft of copper pipe in a 55gal drum of water, then through a generic water trap. So long as the water in this drum is below the ambient temperature, you will pull the moisture out of the air. It is amazingly effective and I have only had fisheyes once since setting it up, and that was because I spent hours spraying that day (primed and painted both wings in a day) and the water heated to a temperature above ambient temperature. I just turned the water on again and cycled some of the water out of the drum, and problem solved. Way cheaper than a fancy desiccant dryer. I hope this helps.
Tom.
 
I have the fiberglass parts about ready to paint.

For most of us, "ready to paint" is determined by spraying the first coat of primer. That's when surface imperfections suddenly stand out.

I would caution against anything which really needs to be sanded off later. There is always a risk of sanding errors, like thinning an edge, or sanding through, spoiling a careful sealing job. The sander will also tend to put some waves in the surface which will show up later, unless the shop block sands a few coats of primer surfacer after sanding.

Beautiful paint is about prep work. Really finish that cowl up through two coats of epoxy primer. Make it perfect. Later when it gets to the paint shop, they can scrub it with detergent, and lightly wet sand just enough to clean and tooth the epoxy primer. Then they will probably shoot one fresh cross coat of epoxy primer followed wet-on-wet by a urethane primer-surfacer, or maybe go straight to the urethane.
 
Thanks everybody for their input! The local paint store near me also suggested the SPI brand. Has anyone here ever accidentally used this and had the temp go below the 65 degrees called for in their brochure? If so what did you have to do to correct it ?
 
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I agree with DanH.
Make it as good as you can before it goes to the paint shop. They will scuff sand it and spray on their own thin coat of primer to make it ready for the final color coats.
There's no reason why you can't continue to work on it and fly it too. Just work on a piece then put it back on.
I use PPG epoxy primer, as well as their off brand Omni, and typically fly the plane for 18 mos to two years before paint with no problems.
It comes in several colors and you can even tint it.
Used to be, there was no UV protection built into the primers, especially white, but if you ask them now they have fixed that issue quite a few years back.
I haven't had an issue with the two part epoxy primer being porous and soaking in oils but if you are worried about that, you can spray on the final coat as a sealer by mixing reducer in with the epoxy primer mix. Ask your paint supplier and they should be able to give you the mix ratios to do that.
Good luck.
 
.....
I haven't had an issue with the two part epoxy primer being porous and soaking in oils but if you are worried about that, you can spray on the final coat as a sealer by mixing reducer in with the epoxy primer mix. Ask your paint supplier and they should be able to give you the mix ratios to do that.
Good luck.

With the Kirker primer just adding some reducer makes it a "low build" or "sealer" application. You can add up to 20% reducer and I found a 5% to 10% addition made it a bit easier to spray, :)

No additional reduction is required, though reducing the 1:1 mix may improve sprayability and will decrease the total film build, which is desirable in situations where a sealer is called for.

If your finish after resin sealing is good as previously recommended then you don't need the thicker coat for block sanding.
 
Thanks everybody for their input! The local paint store near me also suggested the SPI brand. Has anyone here ever accidentally used this and had the temp go below the 65 degrees called for in their brochure? If so what did you have to do to correct it ?

The SPI epoxy MUST be kept at 60* for about 24 hours or you will likely have it go dormant and the cure can't be restarted (requires stripping the coat off). After 24 hours, it will be fine below 60, just slows down the cure.

If you can't maintain 60* for 24 hours, maybe you can find a different brand that offers accelerators to deal with the cold. Accelerators designed for 2k paints won't help, as it is the epoxy component that is the sensitive one.

Larry
 
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Thanks everybody for their input! The local paint store near me also suggested the SPI brand. Has anyone here ever accidentally used this and had the temp go below the 65 degrees called for in their brochure? If so what did you have to do to correct it ?

Spraying epoxy primer below 65 degrees may produce adhesion problems, so the fix would be stripping and repaint. But this would be the same with any epoxy primer not just SPI. It is possible to get good adhesion at low temperatures just not a guarantee. Call Barry at SPI he is the expert and may bve a bike to suggest a work around. But, I will expect that low temps and any epoxy primer is going to be an issue.
 
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