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.