We want to 'dress' up an old concrete sidewalk with pavers, but don't know if we should adhere them with mortar or some type of adhesive material. Which method would be the most durable in the long run?
I have never tried to adhere pavers to a sidewalk, but can't say I wouldn't recommend it. Instead I would install paver edging along the edges of the sidewalk and set the pavers in between them. Then I would fill in between the pavers in with polymeric sand to lock them in.
You typically want pavers sitting on top of a sand and compacted rock base. This allows for some movement as needed and some drainage if needed.
If you are in a freeze/thaw climate, adhering the pavers to the sidewalk likely wouldn't work very well as water will eventually get under the pavers and start cracking everything a it freezes.
Ideally, you're remove the concrete first, then put down the pavers.