How do I replace a 6 inch strip of calk that has mold underneath?

Sandra,. Rip out the caulk, and spray with vinegar, and wipe with paper towels,as not to spread the mold. Next, find a mold spray as Amour One mildew spray "2x the strength. Wear a mask. Mold is very hard to get rid of. After you clean, let the area dry completely. When you put the call back let it dry completely. Shower in the am , and clean it, then shower the next am. Aloha!

My suggestion would be to remove all the caulking then cleaning the area with bleach. When dry, apply new caulk especially made for bathrooms and wet areas. It's better to be safe than sorry. Best of luck.

It isn't too hard to remove old caulk. Use a utility knife along the tub edge to loosen it. If you can get an end up, it may pull up fairly easily. Clean the tub surface with a bit of bleach water and allow to dry well. Take painters tape and put it along the wall and then the tub - parallel to each other, leaving about 1/4" gap opening. Use waterproof caulk. Apply it along the crack and smooth with a dampened finger, wiping extra on a paper towel. Continue along the wall. Once it is done, remove the tape carefully and you should have no clean up. Leave it to dry according to the directions (no bath or shower.

There are a couple of things you can try before removing the caulk.

I have this too and what I did was take some fresh lemon and let the juice from it bleach out and kill the mold, I put the actual lemon slice right on the section and mushed it in, leaving the lemon there. for 25 hours. If that does not work for you, you could dab on white venegar, or hydrogen peroxide, or full strength bleach. But one at a time, rinse well in between and dry the area.

If none of those do the trick, remove the caulking, clean and dry the area well, then re-caulk.