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I really need to replace the sealant around the bath, but I want to do a good job of removing the old stuff first.
The bath is a plastic one, and the walls are tiled.
What's the best way to get the old stuff off without leaving any residue or damage, so that fresh sealant can be applied?
You might have to resort to good old fashioned elbow grease.
The sealant should come off the tiles the easiest, both mechanically by scraping with a plastic edge - the flat edge of an adhesive spreader should be suitable, and if necessary chemically (though I'm not 100% certain what you can use) as the glazed surface will hard to damage.
The plastic bath might cause more problems. I'd start with rubbing or scraping with the plastic edge - but take a lot more care. Chemicals are more likely to damage the surface too. You could try using a plastic safe cleaner.
I bought a kit similar to this one, and it worked rather well for both removing the old caulk and reapplying the new. It's plastic, so you shouldn't have to worry about scratching anything up with it.
This is a great article on how to remove the different types of caulk. It also talks about the pros and cons of different types of caulks when you reseal.
From the article:
Silicone caulk can be removed with a sharp, single-edged razor in a razor blade holder. Be very careful to keep the razor angled low so that you don't scratch the tub or shower pan, especially if it is a plastic or fiberglass. A utility knife can also be used to cut the caulk from between the tiles and the tub if the razor can't quite get it out, especially in deeper pockets and corners! Sometimes, if you have a porcelain tub, little black lines will appear on the porcelain as you scrape off the caulk, even though you know you didn't scratch the surface. These marks usually come off with the alcohol wipe. If they don't, use a little scouring powder or Soft Scrub... with a minimum of water.
Usually bathtub caulking is silicone caulk, which can be a bear to clean off. You can usually peel off most of it, but smudges and remnants remain and I know of no solvent to remove cured silicone.
One tip I read somewhere (I have never tried it) is to use a drafting eraser - you know, the white kind with the paper sleeve. Apparently it will remove the smudges and last bits of clinging caulk. If you try this, report back on how well it worked!
3M caulk remover works wonders- if it's compatible with your tub. It didn't eat our fiberglass tub, but it did eat the acrylic surround. Basically, you throw it on and leave it sit for a few minutes to soften up the old caulk, then scrape.
I use white vinegar for final cleanup. It also cleans up any mineral deposits right beside the caulk. Clean up well as you will want the new silicone to adhere properly.
Walker's answer is the good one. Silcone caulking is soluble in acetic acid, notice the smell of it when applying. And vinegar is 4% acetic acid, you can get stronger stuff at a plumbing supply store, but vinegar works.
It doesn't fully dissolve old silicone, but it breaks the seal between it and the plastic and it doesn't harm acrylic. It does remove lime deposits as well.
We have a fiberglass tub surround and after using a razor blade I used Bar Keepers Powder on it and with a bit of rubbing with a wet cloth it all came off and did not dull or scratch the finish. I will never glue a shampoo holder on again.
I used Lift Off caulk remover to get the bulk of it off. It worked great but getting the residue off was a bear until I tried a Mr. Clean Magic Eraser pad, which took it right off!
