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  #16  
Old 06-14-2005, 07:57 AM
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Quote:
Originally Posted by Wayne Hicks
The nice thing about the Cory technique is
() you get to contour really quick. I can rough contour the wing to 36 grit in less than an hour.
() you can go straight to paint without primer.
I'd read that too, but what about the UV barrier provided by the primer?
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  #17  
Old 06-14-2005, 08:48 AM
Wayne Hicks Wayne Hicks is offline
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You must be asking about fiberglass degradation caused by UV. I'm afraid I don't know the full technical story of "if it does" or "don't worry about it".

What I've HEARD is:

(1) Most of today's paints have enough solids in them to provide an adequate barrier against UV.

(2) It takes years and years and years of UV exposure directly to the raw fiberglass to seriously degrade the strength of the layups. As long as we use a good quality paint, we're fine. No specific UV barrier needed.

Any truth to this? I'm not qualified to say for sure.

Two things I do know.

Parked in the bone yard at Edwards Air Force Base is the AT3, the Advanced Technology Tactical Transport, one of the first planes built by Scaled for a government contract, serial number 001! That was 1988-1989. It's been parked out in the desert in the blazing sun ever since. I have physically touched the plane on several occasions. Except for the paint being chalky, the airframe could be dusted off and flown again. Some of the fiberglass on the upper wing surfaces -- the part facing the sun most directly -- has no paint over it. I could see no obvious signs of deterioration. Still looked good to me.

The Air Force conducted a study of UV exposure for fiberglass radomes. After 18 years of exposure, the AF didn't see any structural deterioration from UV.
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  #18  
Old 06-14-2005, 11:38 AM
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Quote:
Originally Posted by adouglas
Just slightly OT...

Got the latest Cozy newsletter yesterday, and Nat mentions using a high-build epoxy primer from Viking Paint Co. that comes in two colors, which can be mixed to make a third color. He said:

"Using several layers of primier of alternating colors, and sanding in between applications, was very useful in determining when all low areas had been leveled and it as time to apply the finish coat."

Interesting.

It seems like we are mixing apples and artichokes here. The concept of spraying with different colors of primers before sanding has nothing to do with either protection or paint bonding.

When you have sanded (and sanded and sanded.........) and feel that you have the smooth surface you want, you lghtly spray with the primer (entire surface), and sand with a longish block. The low spots, which you cannot identify by feel, will remain primed since the block cannot touch the surface there.

Your decision then is to make the higher lower, or add to the lower and make higher. When done, you should have none of the primer left on the surface and have a smooth surface.

The above material would probably work well if the only thing you do is fill in depressions. You will find that the process involves both. Ideally you want to see the fibers, with the depressions and pinholes filled, over the whole surface.

This, of course is not possible.

The fact that the viking primer is epoxy, and thus possibly harder to sand would tend to interfere with this technique.


This technique is easier and more accurate than the "feel" mehod, although that works too.

After you are smoothed by the above, the Viking might do well.

Smoooooth
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  #19  
Old 06-14-2005, 12:10 PM
Don P-Factor Don P-Factor is offline
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From the CP 77..
A DIFFERENT CONTOUR/FINISHING IDEA
This is presented as food for thought, not as the only way to do it. This idea was developed by Cory Bird, a very bright manufacturing engineer at Scaled. Cory is in the finishing stages of his exquisite original design and came up with this idea while working through the contouring stages on his airplane. I recently refinished my wood core/carbon composite prop and I used Cory's idea and I liked it! It worked great! Here it is.

The idea came when Cory compared the weight of a gallon of epoxy with a gallon of Featherfill. If you have not done this, do it, it will open your eyes! Even taking into account the evaporation of solvents in the Featherfill, there is a huge difference. Anyway, this is a process that starts when you have your airplane (or parts of airplane) structurally complete, in bare glass, and are ready to begin contouring. Sand the glass as usual, you are not looking for a structural bond such as you would need in a glass-to-glass bond, you just need to scratch the cured epoxy. Use at least 40 grit, 36 grit is better. Sand hard in one direction 10 strokes. Then sand hard at 90 degrees to the first sanding in the same area, 10 strokes. This is not a hard and fast rule, it is just a rule of thumb so that you can begin to see the kind of surface preparation you need prior to applying dry micro.

Before applying the dry micro, paint the area with pure epoxy. Wipe as much of this epoxy off as you can with a clean paper towel. This is the "glue" that will bond the dry micro to the cured substrate (skin). A good idea here is to only try to do a small area at a time, say a square foot or two. Mix up a batch of dry micro - the consistency of cake icing works well. Some people try to mix it so dry that it is almost impossible to apply. I don't agree with that. The gram or two of weight you might save per 8 ounce cup is simply not worth the enormous effort. Spread the micro (just like peanut butter) using a squeegee. If it rolls up behind the squeegee, it is a little dry but you can fix that with peel ply. Squeegee through the peel ply to get the micro even and where you want it. Once the whole surface is micro'd, allow it to cure.

Contour sanding should be done using a long sanding block. In the case of a wing, 3 or even 4 feet is not too long. Glue 36 grit sandpaper to the sanding block using 3M 77 spray adhesive. Sand until you hit glass, then stop. If you still have low spots, rough them up, fill them with dry micro and repeat the above until you have the smooth contour you like. Leave it in 36 grit scratches. Do not go to a finer grit sandpaper.

Now, mix up a little pure epoxy and, using a 6" wide soft rubber squeegee, spread this pure epoxy (no micro) all over the surface. The idea is to fill all of the 36 grit scratches with pure epoxy. Carefully squeegee as much of this first coat of epoxy off as you possibly can. Use a lot of force on the squeegee and wipe the edge of the squeegee often with a paper towel. Allow to cure for two hours or so. The first coat should be gelling but not fully cured when the second coat of epoxy is applied in exactly the same way. Continue with this ritual until you have applied five separate coats. At two hours per coat, obviously you will need at least 10 hours at one stretch. Of course, this will depend on the ambient temperature and on what epoxy you are using. Here in Mojave in the summer, using Safety-Poxy or PTM&W epoxy, two hours between coats is sufficient. Allow these five coats to cure for a full 48 hours.

At this point, you have filled all of the 36 grit scratches and you have a very thin film of cured epoxy over the entire surface. All that remains now is to final sand. You should not have any runs or thick lines of epoxy. Wet sand with 220 grit followed by 320 wet. You are now ready to paint! That's it, no Featherfill, no Morton's eliminator, nothing but epoxy all the way. This way, there are no pinholes, no voids, no place for a delamination to start, no place to trap moisture. All you need now is a quality paint. I would suggest at least a high quality urethane or epoxy paint. Keep in mind that your composite airplane is very flexible and will flex in turbulence and while taxiing over bumps. If you use a brittle paint such as enamel or lacquer, it will crack at all highly stressed areas.

For the toughest, most longlasting finish, you should use the same epoxy for the contouring method described here as you used to manufacture your airframe. However, this may be time consuming because sanding Safety-Poxy micro can be very hard work. The only way to speed this up, for those of us who are impatient, would be to use the fast West System (Gougeon Bros.) for the contour job. It will go much quicker, perhaps only one hour between coats, and it will sand much more easily - it will not be quite as tough, but it will certainly be adequate.
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  #20  
Old 06-14-2005, 12:10 PM
Wayne Hicks Wayne Hicks is offline
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The Cory Bird article can be found from the CPs:
http://www.ez.org/cp77-p4.htm
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  #21  
Old 06-14-2005, 12:12 PM
Wayne Hicks Wayne Hicks is offline
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...and it seems that Don and I had the same intent to post at the same cyber time. Amazing.
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  #22  
Old 06-14-2005, 12:24 PM
Wayne Hicks Wayne Hicks is offline
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Epoxy primer? I'm using Valspar epoxy primer and it sands like a dream! Very EZ. Mucho mucho mucho easier than sanding micro.

As for Nat and his 3 colors of Viking primer, I'm sure what he's implying is that you use the different colors as guide coats to let him know when to stop sanding.

While I agree wholeheartedly with the "apply high build to build up the low spots", a guide coat works well for blocking out the final prime coat. For example, the Valspar primer comes in grey and white. I am using the grey Valspar on the initial builds. When I am sure that the surface is leveled out -- you can tell this because ALL of the primer has cross-hatched sanding marks through it -- I will apply the final primer coat with the white color. Thus, as I block out (sand) the white, the gray will just barely start to show up under the white. The grey serves as the guide coat letting me know when to stop sanding. You really want your final primer coat to be all the same color prior to top coat (final paint).
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  #23  
Old 06-14-2005, 01:23 PM
Don P-Factor Don P-Factor is offline
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I concur with Wayne on... the color must be all the same color before Topcoat. The only difference is that I like to use a dark base primer red oxide or black before the contrasting second lighter color. The dark shows any imperfections better before appling your final process primer. Don.
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  #24  
Old 06-14-2005, 07:22 PM
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So what is Nat working on that he needs to sand? I bet its a fat Cozy!
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  #25  
Old 06-15-2005, 11:03 AM
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Quote:
I have physically touched the plane on several occasions.
Okay Wayne, how'd you get into Edwards. I tried this spring and it's impossible to get past the armed guards and barbed wire although I was a "civie".


Primer - Use what you like over the epoxy but BE SURE YOUR FINAL PRIME IS THE RECOMMENDED PRIMER OF THE COLOR COAT. Try not to use a lot of primer as Nat says. Primer and primer/fillers are for VERY light filling. What happens is when your top coat goes on the primer it softens the primer for better adhesion. This bonding to the color top coat causes the primer to "collapse" a little bit. What you get are exposed scratches you didn't see before. Sometimes this happens weeks later after you wheel it out. Then the surface looks dull. It's your paint curing and settling. That's why some body shops use baking booths to speed up the cure time.

Remember the primer is the "glue" that bonds the surface to the color coat. I suggest picking out your color and type of paint you want to use. Then use the manufacturer's recommended primer and ONLY that primer. Talk to a reputable paint supplier and tell him what it's going over. Racing boat builders are a good source too.

Want some fun? Get your paint and practice in an old car. Tell your buddy you'll paint that old junk for free. Don't learn to paint on your plane.

And I've painted a lot of cars with all colors all over them at the same time. There is enough pigment in the top coat. Don't worry about the color of the primer. If you see primer through your paint, you screwed up.
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  #26  
Old 06-15-2005, 11:30 AM
Wayne Hicks Wayne Hicks is offline
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I was badged for NASA Dryden Flight Research Center, which of course is located at Edwards. I was working the Hyper-X (X-43A) flights at the time. Mach 10 baby!
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  #27  
Old 06-15-2005, 01:17 PM
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Quote:
Originally Posted by neverquit
And I've painted a lot of cars with all colors all over them at the same time. There is enough pigment in the top coat. Don't worry about the color of the primer. If you see primer through your paint, you screwed up.
I've painted a few things in my day as well. And I agree.
Whenever I have to paint a surface that flexes, I use an additive that is used primarily for the plastic bumpers on late model cars. It allows the paint to flex without cracking. I have used acrylic enamel and a clear coat using the same additive. Has anyone tried this on the color coat (on a Cozy?)?
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  #28  
Old 06-15-2005, 03:09 PM
Wayne Hicks Wayne Hicks is offline
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Whenever I paint a surface that flexes, I use an additive that ... allows the paint to flex without cracking. Has anyone tried this (on a Cozy?)?

----> I don't think we nned to use flexible paint,......unless....unless we left out some key layups along the way???? :-)
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  #29  
Old 06-16-2005, 11:42 AM
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the paints that are suggested, i believe, will take the normal amount of flex in the airframe, the wings do "flex"

just don't like the idea of filling 36 grit scratches with pure epoxy, goes against my grain. why not sand to 80 or 120 grit??
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  #30  
Old 06-16-2005, 12:36 PM
Wayne Hicks Wayne Hicks is offline
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the paints that are suggested, i believe, will take the normal amount of flex in the airframe, the wings do "flex"

----> and that's my point. Although this entire airplane flexes -- the canard and wings especially -- it doesn't flex enough to crack paint.

just don't like the idea of filling 36 grit scratches with pure epoxy, goes against my grain. why not sand to 80 or 120 grit??

----> I haven't spoken to Cory personally, but I'd be willing to bet it's time saved. Cory's process eliminates sanding cycles and eliminates time spent chasing pinholes.

From 36 git:

Plans Process:--> sand 80, sand 120, fill pinholes, prime, fill pinholes, sand 220, final prime, final sand 400. (4 or more sanding cycles past 36 grit, plus finding and filling pinholes. )

Cory's method: skim coats (which fills 99% of pinholes), sand 220, final sand 320. (2 sanding cycles.)

When I did my wings, I could bring a wing to rough contour in a hour with 36 grit. I had few pinholes, just large scratches. The 36 grit is large enough to "bust up" most pinholes. So far, I find that sanding at higher grits (80, 120) open up more and more pinholes. Tiny ones. They are the hardest to fill because it's harder for primer to flow into them. Primer flashes too quick to fill small pinholes. Pinholes get bridged instead filled. Only to pop later.

I skim coated the tops of my wings with raw WEST epoxy last night. I continue to be impressed at how well the pinholes are filled. I can see the logic in Cory's approach. Just wish I had heard of his approoach sooner.

Saves time would be my guess.
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