I am installing a countertop in my master bathroom using 12"X12" polished marble tiles. I do not want a grout line, but I want the installation to be water resistant. Would it work to install using the butt joint method putting silicone between each tile, then go over the entire counter top with a sealer?

Maybe you didn't notice, but your tiles should have a bevel on all 4 edges. You could put silicone caulk between the tiles while installing them, but then you'd have a small "v" for all kinds of matter to accumulate. I doubt if you'll like that much. You don't want to set them and then caulk with silicone because the silicone will need to be "worked" and it'll smear all over.

What you should do it butt them, (since it's a small area), and grout with a matching un-sanded grout. Apply grout sealer on the entire counter per directions. Don't expect sealer to make anything waterproof or resistant. It's just for easier maintenance, nothing more.

Jaz

Marble does not All have beveled edges.

No, putting silicone between the tiles is not a good idea. Not only can I tell you that you will not like it, but it is not a good installation practise for many reasons. You will need to put a small grout line between those tiles, and use a non sanded grout product.
(If you do not want lines, then consider a solid surace custom cut to fit your counter)

You will also need to consider proper thinset. If you want to waterproof your counter top, the professional way would to use a proper membrane, such as ditra, (som still use cbu, but that doesn't make it water proof) There are other products too for that purpose.

But if you do install a countertop by using marble: Really cheap marble tiles will break often at the viens, so if you go to the trouble, make sure you buy one that are rated well for quality.

Buy extra for waste and "those" oops cuts.
We only use silicon for appliying of joint lines near water area's like behind the faucets at joints (after grouting) and around the sink. A silicone/aryclic combo is better for this application.

You also might to check out Schluter Kerdi and RedGard for waterproofing membrane underlayments. Having had real PITB with previous custom granite projects (three 0 all with big bucks, big hassles for all of that heavy slab and custom cuts and polishing). I'll be using integrated/ combo rectangular sink/vanities (probably a pair of 25" wide Avanity sink/vanity tops), butted up (w epoxy grout) to calacatta tiles (need LOTS of good sealing - (: ) for master bath his n hers vanity unit.

Good luck to us both!

Thanks for the post(s). (And I would certainly welcome the benefit of experience of others who've done similar projects.)