There are a couple of reasons why all this may not last long. First is the
different expansion rates of the two materials you are trying to attach to
each other, the other is that one assumes the fireproof render is at the end
of the day m basically cement, which is not strong for anything but
compression, it might just separate from itself and come away on the trim
after a while. I'm pretty sure when I last looked, which was admittedly a
long time ago now, that most of this sort of thing was actually attached
when the render was being applied or it was screwed through the render to
the wall underneath.
That is not to say of course that a wonder material has not appeared more
recently!
Brian

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From the Sofa of Brian Gaff Reply address is active
"Andy Burns" wrote in message
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Harold Davis wrote:

Can someone advise on what adhesive I need for sticking a steel fire trim
to fireproof render?

No experience of it, but this sounds up to the job

http://www.fortafix.com/fiborclad.html

"Our products are supplied to many industrial users as well as well-known
household names such as Aga Cookers and Baxi Heating"