How do I re-caulk my tub tile that appears to have no backing?

Clean with bleach. Scour! Then apply caulking with wet finger or use surgical glove if preferred. Smooth with wet finger.

How is the wall standing up if there is no backing?

They make a nice little gadget that does a better job than your finger. A flexible pad on a plastic handle makes the job of caulking professional and less mess.

Hi Melanie, Run your finger around the perimeter of the tub to see if there actually is any of the old caulking left. If there is, use a putty knife to loosen and remove it. Then clean the surface well. The next step will be purchasing the caulk itself. For the size of a bathtub, you probably need the bigger tube of caulk. You will also need a caulking gun. Be sure to select the caulk made for kitchens and bathrooms. (That will help eliminate mildew.) Slide the tube into the gun and snip the tip off. Apply the caulk by pulling the trigger of the gun. Run a sample test on a piece of cardboard first to get the feel of the gun. Then run a strip of caulk around the tub. Then run your wet finger to push the caulk into the space and to smooth it out. (You can also buy the small tool that will do this job. Approx 99 cents.) Fyi, you can also watch a tutorial of this exact job on YouTube.com They have tutorials on everything under the sun. I use it a lot. Best of luck to you.

The tile has to be attached to something. Is it soft? Does it flex when you push against it? Could be the the drywall/plaster got wet and is damaged. If so that needs to be repaired first. Then you can caulk.

They make a product called caulk saver for deeper cracks. You push it into the area that appears to have no backing. Caulk over it. If I'm out of caulk saver, I've even used rolled and twisted up newspaper or rolled up paper towels to push in the crack. Push in just far enough to were you add caulk on top of it.

Thanks everyone. Very good suggestions.