Materials
Grout is the weak point in every tiled surface
Tiles do not usually fail. The joints between them, and what is behind them, do.
This works through tiling in the order the parts actually depend on each other.
The short version
- Cement grout is porous unless sealed and will stain and harbour mould.
- Movement joints in silicone are required where surfaces meet.
- Tile hardness ratings describe wear resistance rather than strength.
Grout is not waterproof
Standard cementitious grout absorbs water, which is why it darkens when wet and eventually stains permanently in a shower. Sealing it slows absorption for a period measured in months to a couple of years, after which it needs redoing.
Epoxy grout is effectively non-porous and resists staining almost indefinitely, at the cost of being harder to apply and more expensive. For a shower floor or a kitchen splashback behind a hob, that cost difference is usually recovered in appearance alone.
Movement has to go somewhere
Buildings move seasonally and materials expand differently, so any junction between two planes or two materials needs a flexible joint rather than rigid grout. Internal corners, the line where a wall meets a bath or tray, and the perimeter of a floor are the standard locations.
Grouting these instead of using silicone is the most common cause of the hairline cracks that appear along corners within a year. Silicone is a consumable and is expected to be cut out and replaced periodically, which is a maintenance task rather than a failure.
What the numbers on a tile mean
The PEI rating describes surface wear resistance for glazed tiles and predicts how a floor tile will look after traffic, not whether it will crack. Water absorption percentage separates porcelain from ceramic, and low absorption is what makes porcelain suitable for outdoors and wet areas. Slip resistance is a separate rating again and is the one that matters for a bathroom or a kitchen floor.
A tile can score well on hardness and badly on slip, which is exactly how a beautiful bathroom floor becomes dangerous when wet.
Colour and joint width change the result more than the tile
A dark grout with a light tile emphasises the grid; a matched grout makes the surface read as a single plane. Narrow joints look refined and demand very consistent tiles, since any size variation shows up in the line. Rectified tiles are machine-cut to a precise size and permit narrow joints; unrectified ones need wider joints to absorb variation.
Choosing a narrow joint with unrectified tiles is a common specification error that shows up only once the wall is half tiled.
The substrate decides the lifespan
Tiles are only as stable as what they are fixed to, so a flexing floor or a damp plasterboard wall will crack or debond the tiling above it. Timber floors generally need a decoupling membrane or a backer board and adequate deflection resistance before tiling.
In wet areas, tile backer board or a tanking system behind the tiles is what actually keeps water out of the structure. Tiling straight onto ordinary plasterboard in a shower enclosure is a well-known route to a failure that appears two or three years later.
Taste is not the argument here; how a room performs is.
Living with it
Cleaning grout with strong acidic or bleach-based products repeatedly erodes it and eventually makes the staining worse. A soft brush, a mild alkaline cleaner and drying the surface after use does more for appearance than any aggressive product.
Persistent black growth in silicone means moisture is sitting there, which is a ventilation problem rather than a cleaning one. Where staining reappears within days of cleaning, or tiles sound hollow when tapped, get the installation assessed rather than treating the surface again.
The takeaway
Silicone the corners, epoxy the wet zones, and check what is behind the tile before you blame the tile.
A room that is used will always beat a room that is finished.
Questions readers ask
Should I use epoxy grout everywhere?
It is worth it in showers, on shower floors and behind hobs where staining is likely. Elsewhere ordinary grout, sealed and maintained, is usually sufficient and much easier to apply.
Why does my grout keep cracking in the corners?
Because corners move and grout does not. Those joints should be flexible sealant, not grout, and cutting the grout out and replacing it with silicone is the fix.
