Most caulk jobs fail within a year. Here's how to prep the surface, pick the right caulk, and apply it so it stays sealed for years.
Bathroom caulk fails for one reason: improper prep. The caulk itself is almost never the problem. Here's how to do it right so it lasts years, not months.
For bathroom applications (tub surround, shower, sink), use 100% silicone caulk, not latex, not "kitchen and bath" caulk, not painter's caulk. Silicone bonds to non-porous surfaces (tile, porcelain, fiberglass) and stays flexible as the surfaces expand and contract. GE Silicone 1 in white or clear is the standard choice. Budget $8–$12 per tube.
This is the step most people shortcut. You cannot successfully caulk over existing caulk. Use a plastic putty knife or a dedicated caulk removal tool to scrape out every bit of old caulk. Then apply a caulk remover product (Goo Gone has one) and let sit for 30 minutes. Scrape again. The joint needs to be completely empty.
Wipe down the joint with isopropyl alcohol (90%+) on a clean cloth. This removes soap scum, mineral deposits, and oils that prevent adhesion. Let dry completely — 30 minutes minimum. Silicone will not adhere to a damp surface. This is why bathroom caulk jobs fail.
Apply painter's tape on both sides of the joint, leaving only the gap exposed. This gives you clean, professional-looking edges without requiring a steady hand.
Cut the tip of the caulk tube at a 45-degree angle — smaller opening than you think you need. Apply steady, even pressure as you draw the gun along the joint in one smooth motion. Don't stop and start. Fill the joint completely without overfilling.
Wet your finger with isopropyl alcohol (not water — water doesn't work with silicone) and smooth the caulk with one clean pass. The alcohol prevents silicone from sticking to your finger. Remove the painter's tape immediately while the caulk is still wet, pulling at a 45-degree angle.
Don't use the shower or tub for 24 hours minimum. Silicone needs to cure to reach its full strength and waterproofing properties. Most products say "dry in 30 minutes", that's surface dry, not cured. Wait 24 hours.
Black spots on the surface of caulk can often be cleaned with bleach and a toothbrush. But if you see dark discoloration that appears to be behind or under the tile adjacent to the caulk line, that's mold in the substrate — a sign of waterproofing failure that requires a contractor, not just new caulk.
Trovo matches Greater Boston homeowners with one license-verified contractor, no bidding wars, no guessing. Get matched for free →
Get matched with a vetted contractor in Greater Boston within 24 hours.