The most common causes of discoloured and patchy grouts can include over-watering, badly mixed or contaminated grouts, efflorescence, failure to clean grout lines, colour leaching in pools, and cleaning problems including fallen tree leaf stains. 

Often there is no simple remedy to these problems other than re-installation, so we highly recommend taking the time to understand the project conditions and ensuring good habits during the application process.


Grout needs to be mixed with a specific ratio of water to form a soft, creamy paste. If an installer has added too much water, the colour of the grout will be altered. This is due to changes in the cement properties, as well as a separation of pigments within the mix.  In addition to this, the excess water takes longer to dissipate, leaving the grout looking darker initially before drying and appearing pale with streaks and blotches.  Over watering also promotes the development of efflorescence.

Grout Haze Clean-Up

The clean-up technique of grout haze can have a significant influence on the appearance of the hardened grout. If too much water is used during clean-up, it will change the appearance of the grout with variations in grout colour.

Poor mixing

When grouts are badly mixed, the colorants will not be dispersed evenly throughout the grout, which can again result in a streaky or blotchy appearance. 


As trivial as it may seem, numerous grout colour complaints have resulted from using dirty mixing buckets and/or utensils.  Always use a clean bucket and drinkable water, and make sure your work area is clean before staring a job.


Efflorescence occurs when water rises to the surface of the grout then evaporates, leaving behind salts, which dry as a powdery, chalky or crystalline crust. This process can occur during the initial drying process, or it can result from exposure to concrete poisons, such as chlorides. Some causes of efflorescence include mixing excess water with the grout or applying grout before tile adhesives have fully dried.  Rainwater, run off, and rising damp also bring about the same effect.

Discolouration under sealers

Where a sealer has been applied too soon after grout is laid, the moisture from the grout can rise to the surface under the sealer and produce colour variations and patchiness. For this reason, the grout and adhesive must be allowed to cure for at least 14 days before sealers are applied.

Colour leaching in pools

Where a coloured grout has been used in a pool or chlorinated pond, the chlorine or bromine compounds act as a strong oxidising or bleaching agent and may fade the grout colour over time.  ARDEX recommends that you use white grout in these situations. 

Mould growth

Mould can grow on the grout surface if the area is humid, dirty and ventilation poor. The simplest solution to this is to clean all surfaces regularly and ensure adequate air movement to allow moisture to disperse. ARDEX grouts contain Grout Shield which is added to the grout during the manufacturing process which fights both mould and bacteria. 


Cement-based grouts are porous even when they contain additives such as grout booster. As a result, they can discolour over time with cleaning, which is particularly noticeable when grout is a dark colour.

ARDEX offers grouts for any project in a colour range that complements the latest trends in tiles, from flexible coloured grouts such as ARDEX FG8, to easy clean epoxy grouts ARDEX EG 15, and fine, sand-free grouts. View our full range of grout and silicone products at