Tile & Stone

Lippage, Hollow Spots and Cracked Tile

Diagnosing lippage, hollow-sounding and cracked tile: mortar coverage, deflection, movement joints, and how to replace a cracked tile.

Updated · 3 min read

Most tile failures trace back to three things: mortar coverage, a substrate that moves too much, and missing movement joints. Lippage is usually a flatness or coverage problem; hollow spots and cracks usually point to coverage, deflection or movement.

Silica

Cutting tile and grinding out grout create silica dust. OSHA Table 1 requires wet cutting for saws, and a shroud with a dust collector for handheld grinders used to remove mortar, with respirator requirements by task.[8] See Silica dust safety.

Symptoms

Start with what you see.

Symptom Check first
Uneven edges between tiles Substrate flatness, mortar coverage, tile warpage, offset pattern[2]
Hollow sound when tapped Coverage, bond, substrate contamination
Cracked tile Coverage under corners, deflection, movement joints
Cracked or powdering grout Deflection, grout mix, missing movement joints

Coverage

ANSI A108.5 sets the minimum average contact at 80%, or 95% for exterior and shower installations, with special attention to support under every corner of the tile.[1]

  • Hollow and cracked tile most often come from the wrong notch size and not checking coverage often enough.[1]
  • In one manufacturer's tests, an 18" tile set with a 1/4" x 3/8" notch got about 55 to 60% coverage; back-buttered, 75 to 80%.[1]
  • Pull a tile periodically to check. ANSI calls for combing in one direction and pressing the tile perpendicular to the ridges.[1]

Hollow spots

A hollow sound isn't always a failure. A well-bonded floor can still sound hollow, and real failure is more likely over wood.[5] Common causes of real bond loss include:[5]

  • Expansion and contraction without enough movement joints
  • Poor coverage, mortar applied in dabs, or mortar used past its pot life
  • Paint overspray or sealer on the subfloor
  • Excessive deflection
  • Moisture-damaged or delaminating subfloor

Cracked tile and grout

Cracks usually mean the floor moves more than the tile can.

  • Deflection: the common limits are L/360 for thin-bed ceramic tile and L/480 for thin-bed stone. The Marble Institute of America suggests L/720 for stone.[3] Failures have been seen even at L/600, which is why TCNA bases its recommendations on proven assemblies rather than deflection numbers alone.[6]
  • Movement joints: every installation needs perimeter joints at least 1/4" wide, plus joints at every change of plane. Without them, grout can crack or tile can tent up.[4]
  • Spacing: one maker gives every 20 to 25 ft indoors and 8 to 12 ft in direct sun;[9] another sets a maximum of 20 ft.[10] Both point to TCNA detail EJ171. See Concrete crack and joint repair.
  • Grout: common causes are deflection, grout not packed fully, too much water or additive, and grout packed after it began to set.[7]

How to fix it

Repairs work only after the cause is corrected.

  1. Find the cause first: pull a tile to check coverage, check deflection, and look for missing perimeter joints.
  2. To replace a cracked tile: remove the grout around it, break out the tile with a hammer and chisel, and remove the old mortar beneath it.[11] Wear eye protection.
  3. Set the new tile with full coverage: back-butter it and use the right notch.
  4. Regrout. When repairing grout, remove at least 2/3 of the old grout depth; you can't just grout over it.[7]
  5. Add or restore movement joints where they're missing. Cutting them in after grouting isn't recommended, so plan them into the repair area.[4]

When to replace instead of repair

If the cause is structural deflection or a failing substrate, spot repairs will crack again. Large areas of bond loss need the floor taken up and the cause fixed.

Tools we carry

These cover setting with full coverage and keeping edges flush.

References

  1. Laticrete TDS 196: Trowel selection and back buttering
  2. Laticrete TDS 164: Lippage
  3. Laticrete TDS 123: Deflection
  4. Laticrete TDS 252: Movement joints
  5. TCNA: Hollow or loose tile FAQ
  6. TCNA: Deflection FAQ
  7. TCNA: Cracked or loose grout FAQ
  8. OSHA 1926.1153, Silica, including Table 1
  9. Custom Building Products: Wall installation FAQ
  10. Schluter: Incorporating profiles in ceramic tile applications
  11. Daltile: How-to FAQs

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