I'm working on this right now, too. I had to resort to a small screw driving to the the corners but first I applied a caulk remover over the areas and let it sit for a day to make it much easier. Most came off but I am not worrying about getting every bit off. I used DAP Kwik Seal Tub & Tile Adhesive Caulk and it covered very smooth, easy to clean up and filled in any holes or uneven areas great. Just be sure to cut a small tip off the cault so the bead is fine and easy to fill in the cracks. I also had to do between ceramic tiles and it looks tons better. I can't help on the onyx walls - is it marble or ceramic? I wonder if the Orange cleaner (so popular now) would work and give you a brilliant shine! Good luck

Caulk is very particular to what it adheres to including old caulk. You cant silicone caulk over silicone it has to be very clean of old caulk.

I prefer a laytex acrylic mix. I found it best to buy a tube and try a small spot and make sure it sticks to the material your working with check after drying itll save you time and money as its not a very easy do over project. Dont be decieved by what looks like a good seal try to lightly pry up the edge you would be suprised. I have had to remove a cheap shower stall because the base was incompatible with any caulk I tried, It almost caved in the ceiling from water damage because it worked its way under the sides.

I also found most men will say use silicone because thats what theyre fathers used. Silicone sucks big time. I have bought motorhomes, boats and houses all with premature failure of silicone caulk. The warranty only covers the material if it fails not the pain in the rear it is to clean off and redo.

Marcie

Polyseamseal. Doesn't yellow, crack or peel. We did ours about 3 years ago and still looks like new. Silicone is junk!!!

Can you use Marine Adhesive Sealant in the shower?