Caulk or grout: which one failed in your shower

Tell them apart in two seconds

Press it with a fingernail. Grout is hard and does not give. Caulk is rubbery and dents. If what you are looking at is in a corner or where two materials meet and it is hard, then somebody grouted a joint that needed caulk, and that is why it has cracked.

Why that joint has to be flexible

A bathtub with water and a person in it weighs a great deal more than an empty one. It moves, slightly, every single time. The tile wall above it does not move with it. Anything rigid bridging those two surfaces will crack, not because it was mixed badly but because it was the wrong material for a joint that moves.

Same story where a counter meets a backsplash, where a shower pan meets the wall, and in every inside corner of a tiled enclosure. Those are caulk joints. They always were.

Reading the failure

• Caulk gone black or pink. Surface mildew in the sealant, usually because the room does not dry out fast enough. Cosmetic until it is not. Clean, cut out, replace, and while you are at it work out why the room stays damp.
• Caulk peeling away in one piece. It lost adhesion, which nearly always means the joint was not clean or not dry when it went on. Needs cutting out and redoing properly, not a second bead over the top.
• A new bead over an old one. Very common and always fails, because the new sealant is only holding on to the old failing one.
• Grout cracked in a straight line along a corner. Wrong material in a moving joint. Rake it out and caulk it.
• Grout crumbling across a whole wall. Either the mix was wrong or the substrate is moving. Worth looking at before regrouting, or you will do it twice.
• Grout missing in patches on a floor. Often a loose tile underneath. Press around it and listen — a hollow sound means the tile is not bonded any more.

The test that matters more than any of the above

Press firmly along the joint where the tub or shower pan meets the wall, and press on the tile six inches above it. You are feeling for give. If the tile flexes, or the joint feels spongy, or there is any smell, water has been getting behind it and the board back there is likely soft.

At that point sealing the joint is the wrong move. It traps what is already wet behind a new waterproof line and buys you a year of feeling better about it. The honest answer is that the wall needs opening, and I will tell you that rather than sell you a tube of silicone.

Doing it properly

If the joint is sound and it is just the sealant that has had enough, the sequence is always the same and skipping any of it is why caulk fails early.

1. Cut out all the old caulk. All of it, not most of it.
2. Clean the joint and let it dry. Properly dry — overnight if the room has been in use.
3. Use a mildew-resistant silicone rated for wet areas, not a general-purpose decorator's caulk.
4. One continuous bead, tooled in one pass. Stopping and starting is where the gaps come from.
5. Leave it alone for as long as the tube says before the shower is used. This is the step everybody shortens.

Filling a tub with water before caulking, so the joint is at its widest, is an old trick and a good one for a bath that gets used by adults.

What this costs if you would rather not

A tub or shower perimeter cut out, cleaned, dried and resealed properly is a couple of hours, and small grout repairs get quoted with it. If the test above comes back soft, you will hear that instead of a price.