· by Michael Blair, Nashville's Tile and Stone
Grout is a rigid cement product with no meaningful flexibility. Where an assembly moves, grout cracks — so the location of a crack tells you whether it is a detailing error or something structural.
Why does grout crack in corners?
Wall to wall, wall to floor, and around a bath or tray are all changes of plane where the two surfaces move relative to each other. Those joints should be silicone, not grout.
Grout there cracks within a year and is not a defect in the material — it is the wrong material in that joint.
What does a straight crack across the floor mean?
Grout cracking in a straight line across a floor usually means movement in the substrate beneath — deflection in the subfloor, a slab crack telegraphing up, or a missing movement joint.
Movement joints are required at intervals on larger areas and at perimeters, and they are frequently omitted in residential work.
- Inside corners and changes of plane: silicone, never grout
- Straight cracks across a field: substrate movement
- Crumbling grout: bad mix or premature washing
- Cracks with loose tiles: bond failure beneath
- Movement joints at perimeters and at intervals
Substrate deflection
Tile needs a stiff floor. A subfloor that flexes underfoot cracks grout and eventually tiles, and no grout product compensates for it.
In older Nashville houses with dimensional joists at wide spacing, adding a layer of subfloor before tiling is frequently necessary.
Repair
Rake out the failed grout and replace, and where the joint is a change of plane, replace it with silicone rather than grout.
If tiles sound hollow when tapped, the problem is bond failure beneath and regrouting only postpones it.
FAQ
Why Grout Cracks and What It Means — questions
Should corners be grouted or siliconed?
Siliconed. Every inside corner and change of plane — wall to wall, wall to floor, around a bath — moves relative to itself, and grout is rigid. Grout in those joints cracks within a year. It is the single most common tiling detail error in residential work.
Why is my floor grout cracking in a straight line?
Usually movement in the substrate beneath — a flexing subfloor, a slab crack telegraphing up, or a missing movement joint. Regrouting the line will not hold, because the movement continues. The subfloor stiffness or the joint detail has to be addressed first.
Does cracked grout mean the tile is failing?
Not necessarily. Tap the tiles around the crack — a solid sound means the bond is fine and it is a grout or movement issue. A hollow sound means the tile has debonded from the substrate, and regrouting over that only postpones a larger repair.
How do you fix cracked grout?
Rake out the failed grout and replace it, but read the crack first. In an inside corner or around a tub, the joint goes back as silicone, not grout. A straight crack across a floor means the subfloor or slab is moving, and if the tiles around it sound hollow, the bond has failed and regrouting will not last.