pinkannie Can I suggest that you certainly seal the base wood with pva mixed with a little water and let it dry clear (24 -36 hrs will do it) then, and this is where I would suggest differently to most is, don't use tile grout at all. Use tile adhesive to lay and set the tiles but use an epoxy resin (a two part mix) to grout between the tiles and ensure you finish it with no sharp edges or angles. The reasoning behind that is that the epoxy will be waterproof and mould proof and no sharp edges or angles will facilitate easy cleaning when sugar, crumbs, flour etc. get spilt and might otherwise get trapped between the tiles. Having no sharp edges will make it easy to wipe or sweep clean. You can use a wetted little finger to smooth the epoxy either with water or my preference is with methylated spirit.
Epoxy Resin comes in a variety of setting times from 1 minute to 24 hours. A 3, 6, 12 or 24 hour setting time will give you enough time to get it right.
Hope that helps.