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What to check, and in what order

My grout is cracking, powdering or falling out

Where it fails tells you what failed. A straight crack at a corner or along a perimeter means a movement joint was filled with grout instead of sealant — the grout is reporting movement, not failing. Powdering across a whole area is the mix or the water. Grout gone from one joint with hollow tile beside it is a tile problem.
  • 6Candidate causes
  • Most commonMost likely
  • No — candidates onlyA diagnosis

Where this starts

Grout is a filler, not an adhesive and not a waterproof layer, and most grout complaints are really complaints about something else that the grout is the visible symptom of.

THE PATTERN IS THE DIAGNOSIS. Cracking in a straight continuous line — along an internal corner, where the floor meets the wall, around the perimeter of a room, or over a joint in the substrate — is almost always a movement issue: those positions need a flexible sealant rather than rigid grout, and grout placed there cracks because it is being asked to accommodate movement it cannot.

Powdering or crumbling across a wide area is a material problem instead: too much water in the mix, grouting before the adhesive had cured, or washing the joints down too early and too wet, all of which weaken the grout throughout rather than at a line.

And grout missing from a single joint, especially with a hollow-sounding tile next to it, is usually the tile moving rather than the grout failing — the joint is being worked open by a tile that is no longer bonded.

The reason this matters beyond appearance: an open joint in a wet area is a water path into the substrate, and the substrate is the expensive part.

What it could be, and what tells them apart

These are candidates to check against your own building, in the order they most often turn out to be the answer. None of them is a diagnosis of your situation.

  1. A movement joint filled with grout

    Most common

    A straight, continuous crack exactly at an internal corner, a wall-to-floor junction, a room perimeter, or above a joint in the substrate — following a line rather than appearing randomly.

    How to check: Look at WHERE the line runs. If it traces a corner or a perimeter, the joint needed sealant and got grout.

  2. Too much water in the grout, or washed off too soon

    Most common

    Powdering, crumbling or a chalky surface across a wide area rather than at a line, often with an uneven colour.

    How to check: Scratch a joint firmly. Grout that powders under a fingernail across the whole area was weak from the start.

  3. A tile beneath has debonded

    Common

    Grout gone from the joints around one tile or a small group, with those tiles sounding hollow when tapped.

    How to check: Tap the tiles either side of the failed joint. A hollow sound means the grout is a symptom rather than the problem.

  4. Deflection in the floor beneath

    Common

    Grout failing along lines that follow the joists, or across a whole floor that is noticeably springy underfoot.

    How to check: Walk the floor and feel for movement between supports. A floor that flexes cracks whatever is laid on it.

  5. Joints too narrow or not filled to depth

    Less common

    Grout failing generally but only at the surface, with the joints found to be shallow when raked out, or tiles laid too tight to accept grout properly.

    How to check: Rake a small section out and look at the depth achieved. A joint filled only at the surface has very little to hold it.

  6. The wrong grout for the situation

    Less common

    Failure concentrated in a shower, a steam area, or somewhere chemically attacked, with the grout eroded rather than cracked.

    How to check: What was used, against where it is. Cement grouts and epoxy grouts suit very different exposures.

What to check, in order

The order matters — each step is here because of what it rules out for the ones after it.

0 of 5 checked
  1. 1

    It separates the three families in a single look: a line is movement, an area is the material, and one joint is the tile beside it.

  2. 2

    Those positions require sealant rather than grout, and it is the single most common cause. Regrouting them without changing the material repeats the failure exactly.

  3. 3

    A hollow tile beside an open joint reverses the diagnosis — the grout is reporting a bond failure rather than having one.

  4. 4

    It distinguishes a locally failed joint from grout that was weak everywhere, which decides whether this is a repair or a re-grout.

  5. 5

    Nothing laid on a substrate that flexes will stay intact, so a springy floor makes every other finding secondary.

The calculations behind this

Several of the causes above are a quantity that was specified or assumed. These compute them, with the formula and the standard behind each.

Grout Calculator →Thinset & Tile Adhesive Calculator →Deck Joist Span and Size Calculator →

When to stop and get somebody in

  • Where the floor beneath flexes noticeably — the fix is in the structure, and regrouting a moving floor is money spent on a symptom.
  • Where an open joint in a shower or wet area has let water into the substrate, which is a waterproofing failure rather than a grouting one and will not be solved at the surface.
  • Where the substrate behind or beneath is soft, crumbling or smells, which means the water has been getting in for some time.
  • Where large areas sound hollow, since re-grouting over debonded tiles achieves nothing and hides the extent.

This page lists candidates to check, not a diagnosis — nobody has seen your building. If the symptom involves anything structural, read this first.