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  #1  
Old 06-13-2005, 10:35 AM
Wayne Hicks Wayne Hicks is offline
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Default Cory Bird's Raw Epoxy Finishing Technique

I recently read about the finishing technique that Cory Bird used on his OSH grand champion Symmetry. The technique is dry micro, contour to 36 grit (yes, 36 grit), then skim coat and squeegee up to 5 successive coats of pure epoxy (yes, pure epoxy) to fill all pin holes and scratches. Curious, I tried a variant of it this weekend on the bottom of my wing. 4 pinholes TOTAL! Except for two small low spots near the aileron spars, I was almost ready for paint on the very first try. I am so psyched I can hardly stand it. If I was starting from scratch I would definitely give the full technique a try!

I was already contoured to 120 grit on my wings when I came across the article, so I didn’t use that many coats. In my "test case", I applied the pure WEST with a roller, waited 10 minutes, the squeegeed it all off. The pinholes were almost filled. So I applied another layer, this time lightly squeegeeing to leave a very thin layer. I probably left on too much WEST. I need to find the balance between scraping it all off and leaving barely enough on.

Anyway, I started sanding off the WEST. True, it was a little hard to sand off. But a MIRACULOUS thing occurred. Almost all the pinholes and large scratches got filled. And I'm talking about very big pinholes, like the size of small peas. Even more miraculous, because the WEST is so tough, my 3-foot sanding board (100 grit, then 120 grit) "cut" the tops off the most inconspicuous of high spots that my first contour to 120 never caught! I continued to sand, sand, sand until all the WEST was almost, almost, almost sanded away.

Steve (an exceptional hangar mate if ever there was one) sprayed the wing with primer. Like I said above, I sanded it off and was rewarded with a wing bottom that had only 4 pinholes TOTAL. For test comparison, I didn't WEST the lower winglet. Just sprayed primer over it. Of course, it was loaded with pin holes.

So what does this all mean? Since this is the first time I've ever filled, sanded, and primered ANYTHING, I have no basis for comparison. But I can vouch that skimming with WEST really does fill scratches and pinholes of all sizes. And if you're an aggressive sander like me (meaning, I have no patience, no finesse!), the hard coat left by the WEST helped me to achieve an even better contoured finish. The other obvious benefit is leaving the tiniest of WEST layer helps to harden the micro. I've heard others say that this helps prevent print-through later on in life.
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Old 06-13-2005, 11:21 AM
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Quote:
Originally Posted by Wayne Hicks
I've heard others say that this helps prevent print-through later on in life.
epoxy shrinks, i think print-through is a result of not post curing. i plan on post curing at the final fill. - the info is great and will be used
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Old 06-13-2005, 11:33 AM
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Wayne, in your "before" the new technique, were you by chance using West systems?

I completed (finishing work) my entire LongEZ using West (glass baloons mixed with West 410 filler) and I don't think I had 5 pinholes in the entire plane.

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Old 06-13-2005, 11:56 AM
Wayne Hicks Wayne Hicks is offline
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My dry micro is WEST and microballoons. I've heard the WEST microlight (?) works good and has less pin holes. What is the weight comparion between WEST/micro and WEST/microfil?

Personally, I've reduced the number of pinholes simply by improvements in my technique as I gain experience:

() Dry micro, not too dry, not too wet.
() Following the Prime Directive -- fill low spots and depressions first; do the Big Fill once and only once. Sand to contour once and only once. See my chapter 25 web pages for more explanation about "Prime Directive".

....and the biggie.....

() spread the dry micro with a 6 to 8-inch trowel. Hold the trowel almost flat to surface, pressing very hard to squeeze out the air. I use a heat gun to gently warm the micro before dragging the trowel. I also heat the trowel while spreading by pointing the heat gun onto the backside of the trowel. This makes the micro spread like "butta" (butter).

But I still end up with pinholes like I presume a majority of people do. Waiter, I'd like to hear more about your technique, especially if it reduces pin holes.

Many of my large pin holes came about because I had tried a trowel technique that I couldn't get to work. And that is one of doing the initial spread with a notched trowel, then coming back and knocking to peaks into the troughs. Got rows and rows of air bubbles that way. Others have success with that method. I couldn't get it to work.

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.

Now, maybe Cory can go straight to paint, but I guess I'm a mere mortal who struggles a buit more with the contouring! :-)
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Old 06-13-2005, 12:26 PM
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Mix West 410 in with the balloons, 1 part 410, 4 parts balloons.

I think you'll see a significant difference in how the micro handles.

Its almost like the 410 acts as a lubricant.

The 410 isn't cheep, but it doesn't take a whole lot to get the "lubricant" effect.

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Old 06-13-2005, 01:32 PM
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Quote:
Originally Posted by Waiter
Mix West 410 in with the balloons, 1 part 410, 4 parts balloons.
Waiter
first I heard of this
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Old 06-13-2005, 03:51 PM
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This is an interesting subject, as I was just about to fill my elevators. I had the impression that Poly-Fiber Superfil was the best filler... But Slade had this recent issue with his smooth prime… I’m not certain if this is a quality issue with the primer or the whole line of Poly-Fiber. For those of you whom have used both, which filler did you like the best based on finish, weight, and workability.

Thanks.
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Old 06-13-2005, 04:03 PM
Wayne Hicks Wayne Hicks is offline
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West dry micro (WEST + microballoons) is lighter than Superfill. That's why the four quart kits of superfill are still sitting on a shelf in the hangar.
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Old 06-13-2005, 04:16 PM
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Thanks Wayne. Also, do you think Cory Bird's finishing technique would work on the elevators or is it too heavy? I low vac'd my elevators, so my hunch is that I won't have to worry about weight.
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Old 06-13-2005, 04:26 PM
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Wayne, were was the article published?
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Old 06-13-2005, 04:29 PM
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I used the West, West 410, and balloons, as the filler. Then used Morton Eliminator for the primer.

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Old 06-13-2005, 06:43 PM
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Quote:
But Slade had this recent issue with his smooth prime…
I wouldn't recommend smooth prime under any circumstances. Perhaps it was the fault of the Top Gloss, but why risk it?

I bought a can of superfill and found it 50% heavier than MGS + micro. Still have half a can somewhere.
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Old 06-13-2005, 11:39 PM
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Quote:
Originally Posted by Wayne Hicks
...The technique is dry micro, contour to 36 grit (yes, 36 grit), then skim coat and squeegee up to 5 successive coats of pure epoxy ...
What's 'skim coat' ?
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Old 06-14-2005, 07:56 AM
Wayne Hicks Wayne Hicks is offline
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The Cory Bird article was posted on the Canard Aviators email discussion group. I suppose they got it from the CPs, but I can't swear to that.

A skim coat is where you spread material by barely skimming the surface, thereby leaving the thinnest of material on the surface.

I don't know what to tell you about using the raw epoxy technique on the elevators. I guess it would depend on the quality of your workmanship. I'd fill first with dry micro. I wouldn't use the raw epoxy on the elevators unless unless unless you're diligent about sanding almost of it away (to save weight). I haven't filled my elevators yet, but I understand they're hard to sand, meaning hard to keep at the original shape. The dry micro sands easy. The epoxy does not. Any pinholes can be filled with dabs of raw epoxy or daps of primer.

What's the weight of your elevators? Each one of mine are 25 ounces without the counterweight, 34.5 ounces with the outboard counterweight.
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Old 06-14-2005, 07:56 AM
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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.
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