Tiling Coffee Table Questions

G'day folks,
Have constructed a coffee table (510 x 505mm x ? height) using recycled 18mm Pine and Particle board. I wish to put 6 250 x 150mm tiles on top.
After looking through the forums some have suggested using roof & gutter silicone to save on costs to stick the tiles however this method may cause the tiles to lift especially so with particle board.
So my questions are....

Can one "spread" the silicon instead of using just a dotted gluing fashion on the tiles/ board (as the top has been constructed to allow for the tile thickness & an extra mil for adhesive)?
Does the particle board need to be water proofed beforehand (in case of spills/leaking from liquids spilled on table), and, does the grout need to be waterproof stuff too?


Thanks for any advice given oh and Merry Xmas to one and all.
Woodyknot.