substrate for mosaic tiles around basin

[riv]

I'm making a bathroom cabinet under basin and want to put mosaic tiles on the top, and on the side that backs onto the bath. The areas are small (40 x 20 cms). Can I get away with 6 mm ext ply or should I increase to 12 mm ext ply or should I use backer-board? And what's the best way of fixing and sealing the tiles (they're on a plastic backing)?
Thanks in advance

 

[Richard C]

Use 12mm cement tile backer board (Aquapanel). Problem with using even WBP ply is that it’s still wood & will expand if water gets in, then your tiles will fall off. Use a good quality trade tile adhesive & grout, chepo own brand & DIY products are mostly crap.