Variables that Affect Slip Resistance of Polished Concrete
At the 6th Annual International Concrete Polishing & Staining Conference in Atlanta in September 2013, a panel discussion was organized and chaired by Ken Fisher of Nu-Safe. On the panel were the manufacturer of the BOT-3000E tribometer (floor slip resistance test meter); an Orlando attorney for large international property owners; and slip and fall prevention engineer Dr. George Sotter of Safety Direct America.
Dr. Sotter summarized some of the variables affecting slip resistance of polished concrete. When it’s clean and dry, he said, it’s normally not slippery. When wet, it might be.
Topical sealers can be a problem. Sotter said, “Think about how an ice rink is made. A liquid, water, is spread on a surface, then solidified into ice. When water is put on top of the ice, that’s a very slippery situation. A topical sealer is also a liquid that solidifies, and with water or other liquid on top it can be treacherous.” Penetrating sealers can be OK if applied properly — the surface roughness is maintained. This means carefully removing the sealer from the surface before it dries. Coatings/sealers with aggregates (such as anti-slip abrasive coating SolidStepCote from Safety Direct America) can also provide good slip resistance.
Micro-roughness of the surface can be important and is easily measured, but is not a fool-proof indicator of wet slip resistance; a DCOF test (or dynamic coefficient of friction test) is still needed. Too-rough textures may be harder to clean. Concrete finishes that are honed with a finer grit provide lower wet slip resistance, but safe surfaces can be obtained with a surface roughness fine enough not to detract from the appearance. Color pigments don’t necessarily affect wet slip resistance.
Autoscrubbers (scrubbing machines that use vacuum to pick up the dirty water) are usually best for cleaning — a mop is suitable only for smooth floors without greasy/oily deposits. (A very soft autoscrubber brush, like a carpet brush, cleans effectively with minimal effect on slip resistance. Pads — even nonabrasive ones — tend to pick up dirt and may scar the surface.) A monthly high-pressure cleaning can be helpful. Sweeping may spread contaminants and be ineffective on rougher floors. For applications such as shopping malls, cleaning should be done nightly, but in some other circumstances a weekly cleaning is sufficient.
Even a few layers of floor polish can significantly reduce the wet slip resistance.
The most important step in creating a polished concrete floor that’s slip-resistant is to test from the start of the polishing process. The test must include sealer and polish if they are to be used. Better to find out on the first 10 square feet that there’s a potential problem rather than after the whole job is done! Continue testing as the polishing process proceeds; variable slip resistance is considered a hazard. Since concrete batches can vary, the polishing is an in-situ process, and humans are involved, variation can easily happen.
Safety Direct America (SDA) can help by conducting slip resistance tests on-site. The best wet tests for indoor surfaces use the pendulum DCOF test device, available from Safety Direct America. For a level indoor floor, a dynamic coefficient of friction of 0.37 or higher using the ASTM E303 test procedure is a reliable indicator. Values as low as 0.12 may be acceptable for some areas that aren’t expected to get wet normally in use, such as canned goods aisles in grocery stores. Static friction tests are not reliable indicators of safety and can be very deceptive. For outdoor surfaces, where pedestrians may sometimes run (especially when it starts to rain), the pendulum test is the only test method we recommend as it’s based on 50 years of international research.
A BOT-3000E slip test described in ANSI A137.1 is by reference part of the 2012 International Building Code, applying to ceramic tile. This test, championed by the ceramic tile industry, often gives a higher DCOF than ANSI B101.3 because less wetting agent is used in the water for the test. However, “Tiles with a wet DCOF of 0.42 are not necessarily suitable for all projects. The specifier shall determine tiles for specific project conditions.” Dry DCOF measurements made using the BOT-3000E may also be of interest. Safety Direct America can help with recommendations of slip resistance for specific situations: food courts, restrooms, sports stadiums, outdoor surfaces, etc.
Wet slip resistance may not be important in areas that can consistently be kept dry. Injury claims might still be filed, and it’s helpful to have dry test results showing that the floor is not a safety problem when clean and dry. However, it’s crucial to remember that surfaces that have excellent dry slip resistance are often very slippery when wet. Dry slip resistance is not an indicator of wet slip resistance.
For external surfaces an 80–100 grit finish with a penetrating sealer may satisfy slip resistance requirements.
Whatever the surface, having documented test results for slip resistance at the end of an installation is very important for the protection of all involved. Regular monitoring is also recommended by ASTM E303. Quarterly monitoring by a third party is popular because it roughly ties in with the turnover rate of floor maintenance personnel and/or contracts in many buildings. However, semi-annual or even annual monitoring is better than no monitoring at all. Monitoring reports can be highly cost-effective — they have been shown many times to be very discouraging to plaintiff attorneys.
Safety Direct America can provide initial floor slip resistance testing, monitoring and test reports, signed and sealed by a registered Professional Engineer. Contact John Sotter of SDA at 949-933-6971 for more information on floor slip resistance testing for your property, or for slip tests in our lab for the flooring you plan to use in a new project.
What finish would you recomend for areas that are always wet. They will use the area for cleaning chicken.
Can we use polished concrete till grit 100 only and then use a hardener and sealer?
As discussed by email, hardener is fine. Penetrating sealer is OK as long as none is left on the surface. Whether 100 grit or something coarser is required should be determined by test. It’s critical to polish only a small area — like one square meter — and test it with realistic contamination to assess whether the slip resistance is adequate. Don’t finish the whole area until you have success on the small test patch!
Surprisingly, hundreds of senior citizens throughout the USA are injured by fall each day. So Slip Resistance of Polished Concrete is an important issue.
I have a project that requires a 3000 level polished finish with a non-skid finish. Seem contradictory to me, but it’s specification of a public project. Can you help?
I’ll try giving you a call now. “Highly polished and non-skid” is sort of like saying you’d like to have a “honest and trustworthy politician,” but there are coatings that can give the desired polished look while still being anti-slip…as well as other possible solutions we can discuss.