How to Caulk a Bathtub (Clean, Waterproof Seal)

Cover the tub with a drop cloth first so the surface does not get scratched and old caulk does not fall down the drain. Then take a razor blade or a flat scraper and slide it along the old caulk line at the joint between the tub and the tile.

Keep the blade angle low and make several easy passes instead of digging in hard. You want to cut the caulk free without gouging the tub or the tile. Work the length of the joint until the old bead lifts away.

Push the blade down into the caulk right where it meets the tub. Slide it sideways along the edge and watch to make sure it is actually cutting the bead, not just riding over the top.

If the caulk is thick or there is old caulk hiding underneath, go over the same spot a second time. Any leftover residue keeps the new caulk from sticking, so take your time here.

Now do the same thing where the caulk meets the tile wall. Lay the blade flat against the wall and pull it out just a little so the tip tilts into the caulk as you drag it across.

Keep that outside corner of the blade lifted so you slice the bead cleanly along the whole run. The tub side and the wall side both need to come clean for the new caulk to grab.

Put a little rubbing alcohol on a rag and wipe down every surface where the old caulk used to be. This pulls off any leftover residue and grease so the new bead bonds to a clean surface.

Run a fan or open a window while you do this. The joint needs to be dry before you move on, so give it a minute after the final wipe.

Run a strip of painter's tape along the tub and another along the wall, keeping each line about a quarter inch back from the corner. The gap between the two tape lines is where your caulk bead will sit.

Press the tape down firmly so caulk cannot seep underneath. Straight tape lines are what give you a crisp, professional-looking bead once you pull them off.

Drop the tube of 100% silicone into a standard caulk gun and put a little tension on the plunger. Cut the tip at an angle with a utility knife, starting with a small opening. You can always cut it bigger, but you cannot make it smaller.

Push the long wire on the gun down the nozzle to break the inner foil seal. When you see wet caulk at the tip, you know the seal is broken and it is ready to flow.

Start in a corner and hold the gun level, not tipped one way or the other. Squeeze the trigger with steady pressure and keep the tip moving the whole time so the bead comes out even.

Do not push too hard against the wall and do not race it. Move your free hand closer to the tip for better control. You can release the trigger and re-squeeze any time you need to reset.

Wet the tip of your finger and drag it down the bead in one smooth motion. Start in the corner, keep light and even pressure, and try not to stop halfway. This presses the caulk into the joint and gives it that clean concave shape.

If caulk starts oozing out past the tape, lighten your touch. You will see the void fill in and the surface turn smooth as you go.

While the caulk is still wet, peel off all the painter's tape. Start at the top and pull it up and away quickly. This leaves behind a crisp, clean caulk line with sharp edges.

Keep the caulk dry for the first 30 minutes, then give it a full 24 hours to cure before you touch it or run water on it. After that your tub has a fresh, waterproof seal.