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Prevent aged, cracking caulk around your tub by using grout the next time you seal around the bathtub.
Photos by Joe Provey, Home & Garden Editorial Services
The joint between a bathtub and the wall needs to be carefully sealed to prevent water from leaking behind the wall and perhaps through the floor into the room below. A common approach is to fill the joint with caulk, sometimes labeled "kitchen and bath" caulk. Unfortunately, caulk is difficult apply neatly and usually ends up looking messy. It also tends to peel slightly at the edges creating perfect pockets for mildew and bacteria. That's the black stuff you see. Scrubbing with bleach or high-powered detergents can render the caulk clean, but it's a nasty job-and there is a better way to avoid so many deep cleanings.
Seal the tub to wall joint with grout. It's cheap, long-lasting, looks great, and is better at resisting discoloration due to mildew.
Use tile grout. I used the Polyblend brand. It comes as in powder form, although you can buy tile grout premixed as well. There are two types, sanded and non-sanded. For this fix I'd recommend non-sanded, although either will work.
Follow the steps below for a perfect seal.
1. Clean out the joint with a razor scraper. You will often be able to pull out long segments of caulk once removal gets started. For an old grouted joint, an old chisel may be helpful as well. Don't bother with chemical applications that soften caulk for easier removal. This is just another gimmick to part you from your hard-earned dollars. In most cases, caulk is easy to remove.
2. Wipe away debris. You can use an old toothbrush to help sweep away loose particles. Then sponge clean with vinegar to kill off any remaining traces of mildew. Finally rinse and allow to dry.
3. Mix grout powder with water in a disposable bowl until you have a stiff paste. Go slowly at first: It's easy to put in too much water, in which case you'll need to add more grout. Add only small amounts of water until the desired consistency is reached. Stir the grout for five minutes. Then set it aside and fill the tub with water. The weight of the water will open the joint between the tub and the wall a bit more than it already is.
4. Allow the grout to sit in bowl for 10 minutes. Then stir again and begin to fill the joint. My preferred tool for this operation is a wooden craft stick (a.k.a. popsicle stick or tongue depressor). Use it to press the grout into the joint, and then to scrape off excess grout. Use a gloved finger to give the joint its final shape. The key is that you have the vinyl glove on; and run your finger gently against the grout for a smooth finish. While you're at it, remove old loose grout from between tiles and fill with new grout.
5. Allow the grout to set for about 20 minutes. Then lightly wipe away excess grout with a damp sponge. Use a sponge with a fine texture to avoid pulling grout from between the joints. If the grout dries before you clean it off, you're in trouble. It's tough to remove once it sets. So be sure to wipe the tile clean at the appropriate time. You may now drain the tub.
6. Wait two hours for the joint to harden and remove any remaining grout residue (haze) from surrounding tiles and tub by buffing with cheesecloth. Wait overnight for the grout to become completely dry before using the tub or shower.