PVA on pool paint

Pva is a mixture for area off suction or a pure mild glue for wood
What I look for is a waterproof design like a slurry mix that will help surport your tiles but also seal your backing coat ..first get a power washer or steamer remove ass much access grim .chemical as possible then fill all sensitive areas drains and water inlet pump then cover with a slurry allow a few days to dry or cure then applie your tile then as with any new aqua construction fill and empty pool a few time to cut down any chemical change that can cause thank you

PVA is not suitable to cover over paints. And also not used for rendered services.

It's better use special staff for plaster it's green star for plaster

I would use something more like thistle bond it the green stuff with grit in or the tiling equivalent as provides better key and sealing properties I find just paint on day before you start but I would do more research on background surface first to avoid any bad reactions

I wouldn't. contact a supplier for pool maintenance materials they will have what you need

Is good to use PVA.
The adhesive stick better