Thanks everyone for your help.
I did go ahead and mount it before I saw Bils post. I was/am concerned about the salts also, the advice I looked up at the time was to soak and soak as much as possible and to leave outside in rain etc for about a year.
The cattleya mount I pictured earlier, was an experiment for this reason aswell. I got the pieces at the same time and gave them the same treatment. It has three roots I can see growing into the wood so far so will keep an eye on it and see how they go.
I guess I will just have to remove them if I see problems..
Thanks to all you help I will have several other options/ideas.