How to Caulk a Bathtub or Shower
Remove old, moldy caulk and apply a fresh, watertight bead that looks professional and prevents leaks.
Step-by-Step Instructions
Remove All Old Caulk
Use a plastic scraper or a dedicated caulk removal tool to pry out every bit of old caulk. For stubborn pieces, score along both edges with a utility knife and pull it free. Do not use metal tools on porcelain or fiberglass — they will scratch the surface permanently.
Clean and Disinfect the Seam
Scrub the exposed seam with a bleach solution or mold cleaner to kill any remaining mold spores. Wipe the area completely dry with paper towels. Any moisture trapped under new caulk will cause mold to grow again within weeks.
Remove Residue for a Clean Bond
Old silicone caulk leaves an invisible oily residue that prevents new caulk from sticking. Wipe the seam thoroughly with rubbing alcohol or mineral spirits on a clean rag. The surface should feel squeaky clean and slightly rough — not slippery.
Tape the Edges for a Perfect Line
Apply painter's tape along the top edge of the tub and the bottom edge of the tile (or wall). Leave a gap between the tape edges of about 3/8 inch — this is where the caulk will go. Press the tape firmly to prevent seepage underneath.
Load the Caulk Gun
Cut the tip of the caulk tube at a 45-degree angle. The hole should be about 1/4 inch wide — small enough for control, large enough to fill the gap. Puncture the inner foil seal with a long nail or the puncture tool on the caulk gun. Load the tube into the gun.
Apply the Caulk Bead
Hold the caulk gun at a 45-degree angle with the tip pressed firmly into the seam. Squeeze the trigger steadily and move the gun in one continuous motion. Do not stop and start — a smooth, continuous bead is your goal. Apply slightly more caulk than you think you need.
Smooth the Bead
Dip your finger in soapy water and run it along the caulk bead in one smooth motion, pressing the caulk into the seam and creating a concave profile. Wipe excess caulk off your finger onto a paper towel after each pass. Work in 2-3 foot sections so the caulk does not skin over before smoothing.
Remove the Tape Immediately
Carefully pull the painter's tape away from the caulk line at a 45-degree angle while the caulk is still wet. Pull slowly and steadily. Removing tape after the caulk starts to cure will pull the caulk bead with it and ruin the clean edge.
Clean Up Excess Caulk
Use a damp rag to wipe away any caulk that got on the tub or tile outside the tape zone. For silicone caulk, mineral spirits on a rag will clean it off most non-porous surfaces. Do not use water on uncured silicone — it will smear and never look right.
Let It Cure Completely
Silicone caulk needs 24 hours to fully cure. Do not use the shower or bath during this time. Keep the bathroom well-ventilated. After curing, the caulk should feel firm and rubbery, not tacky. Test by pressing a fingernail into an inconspicuous spot — it should not leave a dent.
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