On 04/25/2010 11:04 PM, William McClellan wrote:
> I have run into an alarming situation. I find epoxy BID applied to
> the firewall material does not have great bonding characteristics.
Well, the description and picture are identical to what I experienced
with the strenghtening and flap drive bonding of one of my wings. In
that whole area all epoxy work just snapped loose if I pried with a
screwdriver.
Disturbing was, that after a second attempt (even more sanding,
cleaning, double checking proper mixture, temperatures, etc.) I got into
the same situation again. For some reason it was impossible to get a
proper bond in that area.
General consensus was that there must have been some release agent
residu from the factory left behind, or silicone contamination from
whatever source (maybe a factory employee wiped off some spoiled coffee
with a contaminated rag?)
So, in the thirt attempt, I not only used acetone, but also soap, gas,
alcohol, vinegar, and a dozen other solvents, to get this invisible and
unknown "release agent" off.
One of these solvents must have worked, because after that the bond was
finally OK.
I just keep wondering how many others must be flying around with a
similar local contamination and never found out about it because
everything just looked right.
Because of this experience I have subjected all my bonds to the
"screwdriver" test. You should pry until you get some fibers off as a
proof that the bond is ok. If you instead hear a "snapping sound" and
the whole layup changes color, you have the dreaded "contamination error".
And yes, my firewall bonds survived the "screwdriver" test. There were
no other problem area's, only this specific area of one of my wings had
this "impossible to bond" problem.
Frans
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