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SEALANTS, GROUT & JOINTS

Grout Cracking

Grout cracks when tiles or the substrate move, joints are too wide, the mix was weak or the wrong material was used at movement joints.

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Fix leaks, movement and moisture before resealing or regrouting

Wear gloves and eye protection. Stop if there is hidden water damage, persistent mould, structural movement or a safety-critical service penetration.

MOST LIKELY CAUSES

Start with these

Substrate movement Flexing transfers stress into grout lines.
Movement joint missing Rigid grout cracks where flexible sealant should be used.
Poor grout mix Too much water weakens cured grout.
Poor adhesion Dust or shallow joints reduce bond.
◫ Symptom variations Match the exact failure pattern and location. ⌄
  • Hairline cracks
  • Crack follows one joint
  • Cracks return after repair
  • Tiles also move
  • Cracks near corners or baths
✓ Quick checks Simple checks before removing material. ⌄
  1. Check for leaks, damp or movement.
  2. Identify the existing sealant or grout type.
  3. Remove only failed material.
  4. Clean and dry the joint thoroughly.
  5. Choose a compatible flexible product.
1 Step 1 — Find the movement source Remove failed material fully and use products suited to the joint, movement and moisture level. ⌄

Check whether tiles, boards or surrounding fittings move.

2 Step 2 — Remove damaged grout Remove failed material fully and use products suited to the joint, movement and moisture level. ⌄

Rake out loose material to a sound depth.

3 Step 3 — Regrout with the correct product Remove failed material fully and use products suited to the joint, movement and moisture level. ⌄

Use flexible grout or sealant where movement is expected.

⌁ Common causes explained Why sealants, grout and joints fail. ⌄

Grout cracks when tiles or the substrate move, joints are too wide, the mix was weak or the wrong material was used at movement joints.

⌘ Advanced diagnostics Further checks for recurring failures. ⌄
  • Check subfloor or wall-board rigidity.
  • Inspect tile adhesive coverage.
  • Use movement joints at changes of plane.
  • Check moisture ingress.
  • Confirm grout compatibility and joint width.
▣ Parts and materials needed Common materials linked to this repair. ⌄
  • Flexible grout
  • Grout rake
  • Movement-joint sealant
  • Grout float
  • Sponge
! When to call a professional Conditions that should end basic DIY work. ⌄
  • Water is leaking into walls or floors.
  • The joint keeps opening because of movement.
  • Mould or damp is widespread.
  • An unvented cylinder, flue or fire-stopping joint is involved.
  • Tiles or fittings are loose or unstable.
? Frequently asked questions Common sealing and grouting questions. ⌄

Can new silicone be applied over old silicone?

No. Remove the old material and residue first for a reliable bond.

Should corners be grouted or sealed?

Changes of plane usually perform better with a suitable flexible sealant.