stevelup wrote:

Is it OK to tile directly onto these surfaces?

Yes, but...


If so, what preparation is recommended.

PVA them first.


Finally, could someone suggest the best tile adhesive
to use?

A nice, sticky wall tile adhesive. Avoid 'adhesive and grout in one'
products. Most of the sheds carry their own brand, I've used several,
and they've been fine.


--
Grunff