How should grout be processed to minimise the risk of discoloration?

Discolouration and staining of grout often occurs after drying. This effect occurs, among other reasons, when the material isn’t processed properly and not under the right conditions.

The colour of grout is determined by the speed at which the material sets. Rapid setting means colour-fastness. Discolouration is particularly noticeable in dark grouts and is something you want to avoid. Most tilers know that cold, damp and draughts can be detrimental. We test grout at around 20 °C and an atmospheric humidity of around 65%. Then if you process it properly, it’s guaranteed to be colourfast. Let’s stress it – if you process it properly.

In practice, it’s a common experience that grouting is started too quickly. It’s sometimes done when the structural work is only half way finished and the building isn’t yet glass-tight. This is often related to the lean project planning that has to be used nowadays. Too much work is done by too few people, which increases the workload. However, it’s better to take your time for grouting. If a room is too cold, place a heater in it for a day until the ideal temperature has been reached. Also pay attention to condensation. Wipe the tiles beforehand with a dry, clean cloth.

Grout contains a lot of plastic binder, which can only be mixed well by machine. In practice, however, we often see that mixing is done manually. For example, it only amounts to a quarter of a bucket, so the mixer is left at home. And then this happens – because manual mixing doesn’t work well, a bit of extra water often has to be added. And that’s also disastrous for the setting time.

I always have a drill bit and a mixing rod in my car boot. Then I show the difference between manual and machine mixing. You really don’t need any extra water with machine mixing. Always adhere to the specifications as they appear on the packaging. By using too much water, the grout sets too slowly and it’s also bad for the waterproofing and hardness of the grout.

Finally comes the sponging off. This is also a tricky job and determines the setting speed. Wait long enough for the grout to set a little first. When almost no grout sticks to your finger any more, it’s time to start sponging. Wipe the tiles with as little water as possible and preferably using a hand sponge. Change the water regularly.