Stop caulking around your tub before you read this, it cost me $480 in water damage
Tbh I see folks on here slapping a fat bead of caulk over old cracked stuff and calling it done, and that is exactly how I ended up paying a guy $480 to replace soggy drywall behind my tub in Amarillo last spring. Water gets behind that old bead and just sits there eating the wall, you cannot see it until the paint bubbles. Scrape the old junk out completely, fill the gap with a backer rod, and use 100% silicone, not the cheap acrylic kind from the dollar bin. Has anyone here had good luck with those silicone tools or do you just run a wet finger like me?
Learned the hard way that a wet finger and I are not friends, mine always drags half the bead back out and leaves a wavy mess that looks like a toddler did it. Silicone tools are worth the couple bucks for the corners alone, but I still finish the flat runs with a finger dipped in soapy water. Big thing nobody says is to wipe the tub edge with rubbing alcohol first, because silicone will not stick to any leftover soap scum or old caulk dust. Sorry about the 480 bucks, Amarillo plumbers must see that soggy drywall all day.