Is it necessary to plaster walls if uneven before tiling. Now that the tradesman has nearly completed works, the majority of tiles look uneven, not a professional finish

Not again ...PVA bad, primer good. Simple as that. See article at the following link for reasons http://www.tilersforums.co.uk/tile-adhesive-grout-substrate-preparation/2511-p-v-versus-primers.html

As a tiler with over 20 years experience you always need a flat surface. Skimming a wall does not always achieve this but it does help on small areas such as kitchen splash-backs etc. If it is a large area like a complete wall, bathroom etc, I always overboard with new moisture-board and tile directly on to the moisture-board once sealed. Unfortunately it sounds like your tradesman has not carried out the above prep work. whether this is the fault of the tradesman, failure to quote or cost saving exercise by yourself I cannot comment. You may have a dispute on your hands.

yes the plaster will need to be sealed with a PVA Based product or watered down PVA else will draw moister out of adhesive and tiles will simply fall off. :)

pva???? :[ on plaster?? before tiling??

if tiling on skim coat plaster with minor damage, should be ok to tile on if bonding coat has been seriously damaged (usually result of stripping off old tiles) aresa needs a replacement bond coat, then apply pva to new plaster pete turner tiler 30years