Oratex Edge Tape Testing

[raystl1]

ummary: Oratex tape needs a layer of extra glue to bond properly on aluminum. Using a tested good primer improves bonding. Bond failures can be repaired with some cyanoacylate glue.




Oratex will be used for my eGull kit I picked up at Oshkosh. Because of things like Martin's experience of poor edge bonding until he applied extra glue, I decided to do some bonding tests.


I used the peel test Oratex has in their docs which consist of a 90 degree pull of the end of a 25 mm strip of fabric. I also wanted to see if prepping with Oratex (non chrome alodine alternative) helped. For all cases the alclad surface was cleaned and scrubbed with maroon scotchbrite first.


The first tests were with plain edge tape, with and without Prekote. I learned two things. Results were scary. For both cases the 'bonded' tape removed about the easily as vinyl electrical tape does. I also learned that Prekote, although proven to improve paint adhesion to aluminum, had no advantage over the bare tape.


Then I tried adding a strip of extra 'normal' Oratex glue along the tape. As Martin discovered, the bond was much better. But neither plain or Prekote versions passed the peel test. Then I learned the strength increases over time. Waiting 24 hours before testing improved the results dramatically. The strength had gone from poor to mediocre, marginally passing the peel test. Waiting even longer improved results a bit more. All subsequent tests had the extra layer of glue applied.


I also tried using a bit of cyanoacrylate (Crazyglue). That gave the best results of any of my tests. The tape fabric was damaged before the bond failed. But it is difficult to use cyanoacrylates for large surfaces.


Oratex states that bonding improves if the metal is painted with an appropriate primer. Tried zinc chromate (Duplicolor rattle can). No significant improvement. Oratex had good results using Rustoleum 360 NT gray primer. I could not find that locally. I did find a solvent based Tremclad Grey Primer (available in Canada) which seemed similar. Results were very good. After a 24 hour wait, the peel test showed results approximately double the minimum. Failure generally consisted of the glue pulling from the tape. Curiously the prekoted sample worked best here. So that is what I will use.


Note that this issue is significant only where an edge is exposed to wind, i.e. the front edge of fabric on the wing D spar. All other cases use full wraps with fabric bonded to fabric.


YMMV.


--Ray

[mkoxxy]

Thanks for doing this, Ray. Have you run this by Lars /
BetterAircraftFabric for comment?

My peel tests did not involve primers - I may have used a little Alumiprep
(etchant). But I roughed up the surfaces more aggressively, with 220 and
150 grit sandpaper (followed by a bit of Scotch-Brite).

After 3 seasons in the sun, I had 3 areas of minor peeling on the wing
fabric edges (top, along center section, 2 and 3" long). They were easy to
fix with a little (fresh) Oratex glue. I think these may have been areas
that I did not roughen sufficiently out to the edge of the masking tape.

The fact that the fabric is still attached to all the ribs (bare aluminum)
gives me confidence.

Martin & the Quark

[raystl1]

Yup BAF has my testing experiences. They have had mixed results trying to get tape to adhere to metal. To quote Joe, "If I were to do it again, I would lay down at least a single layer of glue first. In a nutshell, I recommend you do a test area before committing time and resources."


--ray