Zinc Chromate in 2005

[Michael Horowitz]

I'm looking at a 60 year old Tcraft. She was originally primed with
zinc chromate. If I need to remove some fabric to get at some rust, is
there any reason I shouldn't use ZC as a primer? After all, the last
application seems to have lasted 60 years!
Are there any concerns about any of the Dacron-based covering
processes adhereing to the ZC? - Mike

[[email protected]]

According to the Polyfiber manual, you can prime over the ZC with epoxy
and then the dacron will stick using polytak.

[Michael Horowitz]

Please correct me if I'm wrong, but I believe I've seen multiple
fuselages from the mid-70s that were ZC primed and covered in
Ceconite, so I'm thinking the dacron adhesion to ZC couldn't be much
of a problem! Again, please let me know if you think I'm miss-reading
what I've been seeing - Mike


wrote:

>According to the Polyfiber manual, you can prime over the ZC with epoxy
>and then the dacron will stick using polytak.

[[email protected]]

Yes it can be done, but the solvents in the dope disolves the zinc
chromate primer.
It's better to use a two part primer that the dope will adhere to, but
not disolve.
i suspect that back in the 70's two part primers were not that popular
so the people who covered aircraft used what had been used all along, ZC.

Michael Horowitz wrote:
> Please correct me if I'm wrong, but I believe I've seen multiple
> fuselages from the mid-70s that were ZC primed and covered in
> Ceconite, so I'm thinking the dacron adhesion to ZC couldn't be much
> of a problem! Again, please let me know if you think I'm miss-reading
> what I've been seeing - Mike
>
>
> wrote:
>
>
>>According to the Polyfiber manual, you can prime over the ZC with epoxy
>>and then the dacron will stick using polytak.
>
>

[[email protected]]

The solvents in Stits (Polyfiber) glue, known as Polytak, include
methyl ethyl ketone, which will dissolve primers such as zinc chromate.
The glue is thereby contaminated and diluted and loses some of its
strength. Matter of fact, if you don't prime with Polyfiber's
proprietary epoxy over the ZC the STC is voided.

I'm unfamiliar with Ceconite but understand Polyfiber has bought the
rights to it.