Tile Slip Resistance and COF Ratings

Ceramic and porcelain tile floors can be notoriously slippery. The very feature that makes tile easy to clean—its smooth, non-porous nature—also means that it is slippery underfoot. Add extra tile glazing, water, and dress shoes, and a rush to get to work can mean a trip to the emergency room instead.

But you can avoid slips long before you even purchase the tile. There is a reliable way to find out how slippery floor tile will be under both wet and dry conditions. It's a slip resistance rating system called COF (or coefficient of friction) published by tile manufacturers.

COF slip resistance ratings help you determine if you are buying the right tile for the right location. Along with tile's other benefits, COF ratings are openly available for retail buyers to consult in advance since they are published for every tile on the North American market.

Floor Tile and Slip Resistance

Slippage is a major concern with any type of flooring. Minor slips can have a domino effect that leads to disastrous results. Bathrooms and kitchens are often floored in ceramic or porcelain tile due to the tile's superior ability to stand up to pooled water. But that pooled water can make that seemingly slip-free floor feel like an ice skating rink. 

Home features or issues that you might expect to hurt or kill you, such as electricity, asbestos, or lead paint, are not even close to being the major causes. Instead, slips and falls are the second-leading cause of unintentional fatalities in the home, according to the National Safety Council.

Many of these falls are tangentially related to flooring. People can fall for any number of reasons, such as loose cords, large obstructions, inattention, and physical disabilities. It is also important to note that, within the area of floor-related injuries, only some are related to the floor's lack of slip resistance.

Still, the National Floor Safety Institute says that 2 million fall injuries per year are attributable directly to floors and other flooring materials. Most fall injuries happen on the ground floor, not an elevation.

With those statistics working against you, it makes perfect sense to keep your flooring materials as slip-free as possible. COF ratings are the way to do it.

What Tile Slip Resistance Means

Tile slip resistance is expressed as a coefficient. A coefficient involves two numbers. It is the relation between these two numbers that determines slip resistance. One number represents the force needed to move one surface (such as a shoe) horizontally over another surface (such as tile flooring). The other number represents the pressure exerted between the two surfaces.

Higher COF slip resistance numbers are better than lower numbers. Clean, dry items moving against each other tend to have COF ratings ranging from 0.3 to 0.6. Very slippery items can dip as low as 0.04, with zero meaning that the two items have no friction at all.

Natural stone can be polished and honed until it becomes as slippery as glass. Large commercial and public buildings with highly polished granite or marble floors lay down mats at the first drop of rain. At the other end of the COF rating scale, terracotta tile, quarry tile, or walkway brick have high COF ratings.

How to Improve Tile Slip Resistance

Tile slip resistance can be improved with a number of methods:

• Acid-etching: An acid-etching product can be applied to extremely slippery tile like ceramic, porcelain, or natural stone. It's best to have a qualified professional apply the acid. Most of the gloss will be removed from the tile. Usually, hydrofluoric acid or HF acid is used to dull down the gloss and it must be left on for a specific amount of time at low concentrations.
• Ammonium bifluoride: Another chemical, ammonium bifluoride, has acid-like properties when added to water.
• Mechanical methods: Diamond grinding and shot blasting can be used to improve slip resistance without the use of chemicals.
• Floor mats: Mats, rugs, and runners can be used to improve tile slip resistance, especially in wet applications.
  

COF Ratings Developed in the Lab

Tile companies voluntarily subject their products to testing at independent laboratories that measure skid resistance. Tests have evolved over the years, and the current test, DCOF AcuTest, developed by the Tile Council of North America, is intended to replicate real-world conditions more than the older tests. The older test measured both static and dynamic skid resistance; the current test measures only dynamic skid resistance.

Static resistance means how much force is required to start two stationary surfaces moving against each other. Example: a person standing stationary on a sloped floor. Dynamic resistance refers to how much force is required to keep two already-moving surfaces moving. An example of that is a person walking onto a surface and stepping onto the tile.

DCOF vs. COF: Different Systems

The rating agency, the Tile Council of North America, states that ceramic tiles selected for level interior spaces expected to be walked upon when wet must have a minimum wet DCOF AcuTest value of 0.42." Numbers can be deceptive, as some tile manufacturers still publish older ratings.

• Incorrect: A manufacturer says that its tiles are rated at ≥ 0.60 wet. Because it is specified as the earlier SCOF rating, the tile is still reporting earlier guidelines for safety.
• Correct: A manufacturer says that its tiles are rated at ≥ 0.42 wet. Because this is specified as the DCOF AcuTest, its wet ratings are using the current system.

This does not mean that ≥ 0.60 wet tiles are unsafe. It only means that they are up to spec with the earlier system. In fact, none of these ratings, current or past, address safety. They only list the results of scientific testing and let you derive meaning from them.

COF Slip Resistance Ratings for Other Types of Flooring

When buying tile, you are in luck. With other types of flooring, you may not be able to research slip ratings. Dallas-based lawyer Russell J. Kendzior is a leading expert in slip-and-fall injuries. His National Floor Safety Institute is the go-to place for information about flooring-related injuries. Kendzior says that, except for tile manufacturers, the floor covering industry has refused to test for slip resistance and even create a set of testing guidelines.

Kendzior states that this omission is intentional. In Attorney at Law Magazine, he observes

Floor covering manufacturers see slips and falls as a minefield of liability and avoid discussing the subject publicly. As they see it by not adopting a COF safety standard means that if they are sued, the plaintiff can’t hold them to a standard that in their view doesn’t exist!

Flooring companies may privately test for COF, but they are not required to publish these ratings. In one case, this may be warranted. Unfinished flooring such as solid hardwood is site-finished. Thus, skid resistance is up to the owner since the finishing process is also up to the owner.

The best advice is to ask the flooring retailer if COF ratings do exist for the laminate, luxury vinyl, conventional vinyl, or any other type of floor covering you intend to purchase. They may have ratings on hand that you cannot find online.