Bill from British Columbia sent in an e-mail asking how to remove silicone caulking from his acrylic shower floor. For many years we had nothing that would remove silicone caulking from a bathtub. Then all the companies came out with silicone caulking removers. Then they all disappeared (or will disappear soon) because, although they worked well on ceramic tiles, they did damage to acrylic tubs and walls.
Update 2019:
New product that works
After all those failures, "Re-Mov" - Silicone & Adhesive Remover has come out on the market. This is not a solvent, but is an amazing "bond breaker". It does successfully break the bond between many adhesives and the substrate. What is great is that it is safe for both fiberglass and vinyl - and most rugs! It will even clean up Polyurethane Adhesives! I've tried it. It works. www.Re-Mov.com
Working with the Re-Mov company, I learned some surprising things about silicon and glass. Silicone, be it a caulking bead or a messy finger print smudge, actually reaches down into the microscopically rough surface of glass to get its good grip. But when you try to shave that off, or solvent it off, you don't get what is below the surface -- and that always shows up as a smudge. In fact, that little residue can prevent more silicone from sticking to the same glass. The same is true for many adhesives. Since Re-Mov is not a solvent that attacks the silicone itself, the silicone all stays connected to silicone, and the bond between the silicone and the glass is broken. Now you can pull a bead off the glass and all the little grips in the glass come up with it without any reside left behind, or simply wipe off that silicone fingerprint smudge in the middle of the window.
The problem we still have when we want to re-caulk a bathtub is that new silicone caulking will not stick well to old silicone caulking. Hence you must completely remove the old silicone, even the little residue that is left when you cut it off. But all hope is not lost. In talking to the technical department of one of the caulking companies we came up with two solutions to the problem if you do not have the new Re-Mov chemical product to get a clean surface by simply wiping.
Flower paste to the rescu
Start by cutting off as much of the old silicone caulking as you can. Then make a thick paste with ordinary flour and water. Don't use whole wheat flower, we need the good old fashioned sticky stuff. Take this dough-like putty and rub it over the bit of silicone that is still forming a film on the tile or tub. This dough will roll the silicone up into itself and then you can rinse off the dough -- leaving a clean surface ready for new caulking.
Re-purposing old Crepe shoes
Even more reliable is to use crepe as an eraser. You can actually purchase crepe blocks designed for cleaning sandpaper from such woodworking stores as LeeValley.com or you can simply use old crepe shoe soles. The silicone tends to roll up under the crepe, leaving the surface well 'erased' and ready for fresh caulking.
The power tool solution
If you are cutting away caulking often, the Oscilating power tool does this efficiently with the flexible scraper blade.