You ran a finger along a joint and it came back gritty. Or a piece of grout dropped into the tub while you were cleaning, and now there is a gap you can see from the doorway.
That is one of three things, and the three have almost nothing to do with each other. The grout was weak before it finished curing. The grout is sitting in a joint that was never meant to hold grout. Or something under the tile is moving, and the joint is the first part soft enough to give. One of those is a Saturday. One is an afternoon and a sealant gun. One means tile comes off a wall.
The pattern tells you which. Read it before you buy anything.
Read the joint before you buy grout
Three questions, all answerable standing in the room.
- What is coming out? Powder and loose sand that crushes under a fingernail is a different failure from hard chunks that break away in pieces. Powder means the cement paste never got strong. Chunks mean something strong is being broken.
- Where is it coming out? Scattered evenly through the field, wet areas and dry ones alike, is one answer. A single clean line — an inside corner, the joint against the tub, a run carrying straight across several tiles — is another. A patch, with sound grout all around it, is a third.
- What does the tile beside it do? Tap across the field with a knuckle or the edge of a coin. Bonded tile gives a dull, tight tap. Tile with a void under it rings hollow, like tapping a box. Then press it with the heel of your hand. A tile that shifts, clicks or rocks is not stuck down.
Powder, scattered, tile solid: the mix. A clean line, everything else intact: the wrong joint. Chunks in a patch with hollow tile beside them: the bond.
Cause one: it was weak before it cured
Grout is a mortar. Cement needs water to hydrate, not to be soupy. Past that narrow band the extra water leaves voids behind as it evaporates, and what is left is the same sand and pigment with far less cement holding it together.
Three habits put it outside that band. Mixing loose, because loose grout floats into the joints faster. Retempering — splashing water into a bucket that has started to stiffen instead of throwing it out and mixing fresh. And washing off too early or too wet, so the sponge drags cement paste out of the top of every joint and leaves the sand. A fourth is the room: grout rained on before it cured, which in a shower means somebody used it.
How you tell
Pick at a joint in the driest, least used spot the tile reaches. Behind the door. The floor under the vanity. A course above the shower head where water rarely lands. If it powders there too, the room did not do this — the mix did.
Weak grout fails evenly, which real failures never do. The whole field gives up at about the same rate, and the color often reads blotchy or paler than the sample because the surface was washed open. Vacuum a joint and you get sand. Come back next week and you get more sand.
Check the depth before you commit to anything. Scratch into a joint with a screwdriver tip: hit hard material almost at once and the damage is only at the surface, with a sound joint underneath it.
What makes it fail faster
Acidic cleaners dissolve cement. Vinegar, scale removers and anything sold to attack hard water etch a joint every time they are used, and weak grout has no margin to lose. Handheld steamers do it mechanically. A joint that stays damp between showers stays weak, so if the mirror is still fogged an hour later, the fan is undersized or ducted badly and that is part of this.
What it takes to fix
This one is yours, on two conditions: the tile sounds solid, and the joints are dry a day after the last shower.
The work is in the removal. Old material comes out mechanically, down most of the depth of the joint, with a carbide rake or an oscillating tool and a grout blade — not scratched at the surface. Then vacuum, wash, dry. New grout bonds to clean tile edges and to nothing else. Match the grout to the joint width on the manufacturer's data sheet, because unsanded grout in a wide joint cracks the way the last batch did. Do a whole wall or a whole floor at once, because a patch never quite matches its neighbor, even out of the same bag.
Cause two: it was never a grout joint
Cement grout is rigid. It does not stretch, and in a joint where two things move independently it fails on schedule — a hairline first, then loose crumbs, then a gap.
The joints that move are always the same ones. Every inside corner where two planes meet. The perimeter where tile meets a tub, a base or a countertop. The wall-to-floor joint. Anywhere tile runs into a different material. And on a floor, wherever tile crosses a control joint in the slab. Those want flexible sealant, and which joints those are and what belongs in them is worth reading rather than repeating here.
How you tell
Geometry gives it away. The failure is linear: one straight run lets go — a corner top to bottom, the full length of a tub, a line carrying across several tiles without deviating — and the field either side of it is solid. Grout out of a movement joint often comes away in lengths rather than dust, like a dried rope, with one clean face where it released from the tile.
Then look at what sits on each side of the line. If the answer is "the wall and the floor", or "the tile and the tub", it was never a grout joint.
What it takes to fix
An afternoon, as long as what is behind the joint is dry. Rake to bare tile edges, clean off every trace of the old material, dry it, and tool a pure silicone bead into the joint rather than heaping it on top. Fill a tub before you seal it and drain it once the bead has skinned, so the joint is sealed at the width it will live at.
What is not a repair is grout. Not fresh grout, not the flexible grout on the end cap at the hardware store, not epoxy. Harder material in a moving joint does not stop the movement — it relocates the damage to the tile edge. If someone proposes regrouting a corner that has already failed twice, that is a tell.
Cause three: something under the tile is moving
Grout only breaks into chunks when the tiles either side of it work against each other, and tiles do that when what they are stuck to has stopped holding them flat. Either the substrate got wet and lost its strength — paper-faced drywall in a wet wall softens, and the tile ends up hanging on a board turned to felt — or the tile never had full thinset coverage, and the voids let each tile flex on its own. Both end the same way: independent tiles grinding a rigid joint into gravel.
How you tell
Chunks, in a patch, with hollow tile beside it. Not the whole room, not a straight line, one area.
- Tap it out and map where the hollow sound starts and stops. If that zone matches the area losing grout, you have your answer.
- Press the tiles at the edge of the patch. Movement under hand pressure, a click, or an edge standing proud of its neighbor when it did not before.
- Watch how fast it comes back. Clean a joint out and vacuum it. Fresh debris within a week or two, with nobody picking at it, means it is being generated rather than left over.
- Look for water telling on itself: grout that stays dark in one patch long after the rest has dried, white crystalline powder at the joints, a damp line at the bottom course, a stain on the ceiling below.
- On a floor, stand on it. Tile that gives underfoot is deflecting, and the tile is reporting the framing. That is a subfloor problem, not a tile problem.
What it takes to fix
Not a Saturday. Nothing done to the top surface lasts, because the failure is not on the surface, and regrouting debonded tile destroys the only evidence you had about how far it ran.
The real repair starts as exploration. Tile comes off in the bad area, the substrate gets read wet or dry, and how far the damage runs decides everything after it. Sometimes it stops at a few tiles. Often it does not, because water travels along a bottom plate much further than it travels up. If the wall is a shower and the board behind it is soft, that shower comes out — you cannot rebuild the waterproofing that was supposed to stop this from the room side, through the tile. Around a tub the origin is usually not the field at all but the joint where tile meets the tub flange, which is built wrong more often than it is built right.
Some of it has to be opened up to know
A tap test, a probe and a look at the ceiling below separate the three causes most of the time. None of them tells you how far the third one runs. Nobody can say that from the room side, us included, and anyone quoting a number without opening something is guessing at your expense.
So we pull a tile in the worst area, or take the shower door off and read the joint behind it, or cut a small opening in the back of the wall where it lands in a closet instead of a finished room. Then a moisture reading against a known dry wall in the same house, because the absolute number means little and the difference means everything. In an older Hamilton County house that sometimes turns up a bathroom tiled straight onto drywall. We would rather say that standing in the room than after the tile is off.
When it belongs to another trade
Water that arrives without anyone using the shower is plumbing. If a joint goes dark on a schedule that has nothing to do with bathing, or a ceiling stain grows during a dry week, the leak is in a supply line or a drain, and a plumber finds it faster and cheaper than a tile crew does. Tile set over an unfound leak is money set on fire.
A floor that moves across a whole room, a span that bounces, a crack running the length of a slab: structural, and read by someone qualified to say so before any tile decision gets made.
If there is visible growth or a smell, that is a testing question. We do not test, diagnose, remediate or abate mold, and we will not tell you what is or is not a health risk in your house. The EPA publishes homeowner guidance on mold and moisture, and an independent testing firm — ideally one that does not also sell the remediation — can tell you what you have. What we fix is the water that fed it.
What the far end costs
A regrout is a bag of material and a weekend. A failed shower is a bathroom. Those are not adjacent numbers, which is the reason to read the pattern before buying grout on Saturday morning. For scale on the far end: independent research on this market — Angi's Indianapolis bathroom cost work and published Greater Indianapolis contractor cost guides — puts a typical bathroom remodel around $10,000, with most between roughly $5,700 and $14,700. Crumbling grout is nowhere near that. It gets there when it is left long enough to reach the framing.
The short version
Powder everywhere with solid tile: regrout the surface properly and it is done. A clean line with everything else intact: that joint wants sealant, not mortar. Chunks in one patch with hollow tile beside it: stop, because the problem is under the tile and the joint is only reporting it.
If it is the third one, or you press a probe into a corner and the board behind it is soft, the next step is having somebody read the assembly rather than the joint. On a bathroom remodel the waterproofing and the joints are their own stage of the work, before any finish material arrives. If you want us to look at yours, ask for an estimate and we will walk it with you.
