On Mon, 13 May 2019 05:40:11 +0100, Bill Wright wrote:

Is premixed waterproof tile adhesive in a sealed tub still ok if
it's still unset? It's many years old.

Probably not after "many years".

I'd better test it methinks.

You can't.

You can take a sample squidge it onto the wall intended for the tiles
and see what happens.

Does it set in about the right amount of time?
When set is it stuck to the wall?
When set is it a hard solid layer?

If the answer to all those is "yes" the chances are it's fine.

--
Cheers
Dave.