There’s a myth that tile manufacturers (especially manufacturers that sell tiny tiles) want you to believe, but it’s just a myth. There’s no science or proof behind the statement that more grout lines makes a floor safer. More grout lines doesn’t actually add any slip resistance to a floor with tiny slippery tiles on it, but lots of tile consumers have been fooled by this lie over the decades, causing countless avoidable slip and fall injuries to innocent people.
If the grout is applied so that the level of the grout is exactly even with the top of the tile, and the grout remains at that level for the life of the floor (and is never worn down with floor scrubbers and acidic cleaning chemicals), then the “more grout lines makes it safer” lie would theoretically make some sense. But the grout is almost always slightly below the level of the tile immediately after installation (even half a millimeter puts the grout below the surface that’s actually coming in contact with people’s shoe soles), and through industrial cleaning practices, the grout usually sinks even further below the level of the floor. If the grout is not at the exact same level as the top of the tile, then it’s not adding any grip – the grout is below the surface that people’s feet are touching and therefore the grout is irrelevant.
Grout would theoretically add a bit of grip to the floor if the grout were to maintain its height in relation to the top of the tile (exactly even with the top of the tile for the life of the tile), but it would only add a few millimeters of slip resistance here and there. Slip and fall accidents can happen when someone slips (or hydroplanes on water) just a few inches, so the fact that there are grout lines here and there won’t help stop slips. One study found that a slip of three inches resulted in a fall 50% of the time for young adults (for older folks, a slip of three inches presumably leads to even more falls, and falls can happen with just a couple inches of slipping).
So to have a grout line just below the top of the tile every few inches (or even every one inch) isn’t really adding anything. Only if the grout was maintained to remain for the life of the floor at the exact same height as the height of the tile would this theory work. The grout always recedes below the height of the tile over time, so the theory is a myth created out of thin air by tile salespeople to help sell slippery tiny tiles. There’s never been any documented proof that grout can be maintained in a way that it will never fall below the height of the tile it’s surrounding.
The health club floor shown both above and below in the photos has two inch tiles because the building owner fell for this marketing myth, and everyone from the staff to the members agree: the floor is slippery. The pendulum floor slip resistance test put this floor in the “high slip potential” category, with a pendulum test value of 22, or a dynamic coefficient of friction (DCOF) of 0.22. People were complaining regularly about this floor. They had slips and complaints regularly. So we know from the people that were walking on it daily that it was slippery. Their answer was to keep a “CAUTION” sign up year round. Far from a perfect solution!
After 20 years of testing floors for slip resistance, I’ve come across a thousand floors that have caused serious injuries to people. Many of those floors had one- or two-inch tiles because the building owner fell for this myth. The “more grout lines makes a more slip resistant floor” myth is just that: a myth. It doesn’t work.
Testing floors for slip resistance with reliable slip resistance test instruments, such as the pendulum tester and the iAlert (SlipAlert) tribometer, has shown me countless times that slippery floors remain slippery even if there’s lots of grout lines around the tiny slippery tiles. Often, I’ve been called to test the floors because the building owner knows the floor is slippery – they’re getting slip accidents and complaints. The floor slip resistance test results just confirm what is already known about the tiny tiles with lots of grout lines – it’s a slippery floor.
A slippery tile can’t be saved by increasing the amount of grout lines. It’ll still be a slippery floor.