Is there a Slip Test for Tiles and Stone?

Years ago, when I used to work in a tile shop, one of the most often-heard rejections to ceramic floors was “they are slippery aren’t they?” (the other being “they are cold aren’t they?). The problem for the tile industry back then was that the only other type of flooring that people could compare was carpet or some kind of vinyl flooring.

In order to determine how likely a floor it to have a problem, we can conduct a slip test, (such as a Pendulum test), but more of that later. In actual fact, there are so many things that can affect how slippery a floor will be (and now of course I am talking about any hard floor be it ceramic, stone or resilient (Vinyl) that it is not a simple task to classify a flooring as slippery or not. All of the following must be taken into account when choosing a suitable floor.

1. The situation – what is the room or floor going to be used for?
2. Will it be mostly dry or wet?
3. What will the cleaning regime be?
4. What type of foot-ware will be worn?
5. What contaminants will the floor be exposed to?

And so on.

Let’s just take one example of why it is not so straight-forward: One popular profile for sports-hall changing rooms is a stud profile – giving the tile somewhat of a utilitarian look, and a bit like a bar of chocolate. This is designed to work best with bare feet; the blunt studs will push into the soft foot which will form around them and get a good purchase on the tile, even in the wet. So it is very good anti-slip floor right? Well, take the same floor and walk across it in hard leather soles – soles that cannot deform and ‘hug’ the studs, what happens now?

Similarly, think about a pair of football boots (or golf shoes if you prefer) they have studs on the sole. When used on the surface that they are designed for i.e. soft grass, they dig in and provide very good grip. Have you ever walked across a hard, flat and smooth floor in studs? – how much grip have you got now?

In both these cases, if the wrong foot-ware is used on the wrong surface, it can result in a greater chance of slipping, not less. The surface area contact between the stud on the football boots and the hard floor (just like studded tiles with flat shoes) is reduced, therefore lowering the amount of resistance, result – greater chance of slipping.

It should also be said that most hard surfaces commercially available, usually give pretty good results in terms of slip resistance – at least, in the dry. But dry situations are not normally the problem, it is when a floor is wet (or contaminated with some other lubricant like oil or grease for example) that floors can become more risky.

The most obvious thing to say here is that we are really not slipping on the floor at all, we are slipping on the water, or the grease etc. So surely the most effective way to reduce or prevent slip-fall accidents is to keep the floor clean and dry? – Absolutely! However, we also know that floors are not kept clean and dry all the time.

So how do we decide? Well first of all we need a method for measuring the resistance to slipping, or conversely, the slip potential of a floor. There are various methods but we can measure the amount of resistance to slipping, by measuring the amount of friction a floor generates when walked on. This is measured as a coefficient of friction or CoF. Using a piece of kit called a TORTUS (a kind of motorized box on wheels that drags a special rubber foot across a floor) we can measure the CoF of that floor. If we get a reading or CoF value of 0.20 or above, then the slip resistance of that material can be said (in pure guideline terms) to be reasonable for normal situations. The old recommendations for areas where a bit more risk is present (like changing rooms, or the walkway around a pool) called for a minimum of 0.40. to put this in perspective, most unglazed ceramic tiles will give a reading in excess of 0.50 – but this is all in the dry. Ceramic tile manufacturers often list the dry CoF information in their catalogues.

Today, the preferred method for ascertaining a floor’s ‘potential for slip’ is the Pendulum Test Method. This pendulum device has a swinging arm carrying a rubber foot, which is allowed to strike the floor, when it comes to the top of it’s swing, it leaves behind a pointer. The pointer reads off a special scale to give a Pendulum Test Value or PTV. Several readings are taken, in 3 directions, first in dry conditions, then the test is repeated in wet conditions. All the results are recorded then an average for both dry and wet are determined. In an attempt to try to simplify things the HSE’s recommendations are that anything with a PTV of 36 or above has a low potential for slip. As the wet result is usually lower than the dry, this is the result to look for, if your chosen material has a reading of 36 or above, even in the wet, then it has a low potential for slip. But as I pointed out earlier – don’t forget to take all the other things into account when choosing your floor.

For anyone wanting to learn more about this then there is a great article here: http://www.hse.gov.uk/pubns/web/slips01.pdf

Copyright Ian Taylor and The Tile and Stone Blog.co.uk, 2013. See copyright notice above.