Grout Crumbling Out Of A Tiled Floor

What's happening?

Grout is a filler between tiles, not an adhesive and not a waterproof layer, and it fails in ways that point at different causes. Grout that rubs away as powder was weakened as it cured — usually mixed too wet, or washed and polished off before it had gained strength, so the cement never developed properly. Grout that comes out in clean lengths along one line was not weak at all: it was being asked to absorb movement, and a rigid material in a moving joint always loses. Grout that is only failing where tiles sound hollow is being flexed by the tiles themselves. Grout is classified for use under BS EN 13888, so a floor that sees water and traffic needs the right class rather than whatever was in the van.

What usually causes it?

• Grout mixed too wet, or extra water worked into the surface while cleaning it off, weakening the cement as it cured
• Cleaned or polished off too early, before the grout had gained enough strength to hold together
• The wrong grout class for a floor that sees water and traffic, when a stronger or water-resistant grout was needed
• Movement being taken by the grout because the perimeter and intermediate movement joints are missing
• Grout used in an internal corner or at a wall-to-floor junction where flexible sealant belongs
• Voids under the tiles, so the tiles flex and grind the joint apart from below
• Joints too narrow for the grout to have any real depth or body, particularly with large tiles

When should you call a tiler?

Call a tiler where grout keeps failing after being replaced, where it is coming out along one continuous line, or where the tiles around it sound hollow — all three mean the joint is reporting something else. Call before regrouting a whole floor, since it is worth knowing whether the answer is grout, movement joints or relaying, and regrouting a floor twice costs more than doing it once. Call promptly where a kitchen, utility or shower floor has open joints and water is getting through.

What will the tiler actually do?

• Establish whether the grout was weak, is taking movement, or is being flexed by tiles with voids beneath them
• Tap the surrounding tiles for hollowness before deciding whether regrouting will hold at all
• Rake out failed grout to full depth with dust control rather than filling over the remains
• Regrout in a class suited to that floor, mixed to the specified ratio and cleaned off only once it has set
• Replace grout with flexible sealant at internal corners, wall-to-floor junctions and perimeter movement joints
• Form the movement joints the floor lacks, so the grout is no longer the part absorbing the movement