What a wet pendulum test value tells you
A Pendulum Test Value (PTV) is the number a pendulum tester gives when a rubber slider is swung across a wet surface, and it is the figure behind most slip-resistance claims you'll see on a tin or a datasheet. The UK Slip Resistance Group reads that number against three bands.
The three bands
- Below 25: a high risk of slip.
- 25 to 35 inclusive: a moderate risk.
- Above 35: a low risk of slip.
Higher is safer on this scale. The low-risk band above 35 is sought using the 4S rubber slider, also sold as the number 96 slider, for most floors, and the TRL rubber slider, also known as the number 55 slider, for areas where people go barefoot.
What the group says about using the figure
The UK Slip Resistance Group states that pendulum testing should not be considered to provide a pass or fail value. The legal requirement is that a surface is safe. A product sitting above 35 tells you where it falls on the scale. It does not, on the group's own wording, tell you that the surface is safe in every condition it will meet.
The three risk bands compared
A pendulum reading places a surface into one of three bands. None of the three tells you whether a specific tin of paint will pass or fail on its own.
| Risk band | What it means | Question to ask |
|---|---|---|
| High risk | The surface is more likely to feel slippery underfoot when wet. | Which rubber slider the test used, and whether the surface was tested wet. |
| Moderate | Some slip risk remains, and where in the band a result sits can matter as much as the band itself. | Whether the figure given sits near either edge of the range. |
| Low risk | The surface is less likely to feel slippery underfoot when wet. | The test was carried out on this substrate. |
The UK Slip Resistance Group states that pendulum testing should not be considered to provide a pass or fail value, and that the legal requirement is that the surface is safe. This table sets out the bands as a guide to a reading.
Where the published bands stop short
The bands most people reach for when judging a wet surface were worked out indoors, and nothing published alongside them says how far that still holds once the surface is outside.
The bands are written for floors
The UK Slip Resistance Group's bands were drawn up for floors, and the group's own guidance says nothing specific about external surfaces. A patio is wet more of the year than a kitchen floor ever is, it can freeze, and it grows algae in a way an indoor tile doesn't. None of that is addressed in the bands themselves.
The same apparatus, a different standard
The pendulum used to produce those floor bands is also the apparatus behind EN 13036-4, which is the standard written for roads and airfields. A pendulum test value quoted against EN 13036-4 for a patio or path was tested to the vehicular standard. Worth asking which standard a quoted figure was actually tested to before treating it as an answer about a patio.
Trade coatings publish slip figures. Patio paint often doesn't.
Sealant and coating ranges sold to tradespeople often carry a slip-resistance figure on the datasheet. Watco, a sealant supplier, publishes a pendulum test datasheet citing BS 7976-2 with values for at least eleven coatings, the highest of them reaching 78.2. A Pendulum Test Value (PTV) comes from swinging a rubber-tipped arm across a wet surface and recording how much drag slows it down, so a higher number means a surface that grips better underfoot.
Patio paint is a different story
Whether the paints sold straight to homeowners for patios and paths carry the same kind of figure hasn't been measured here. Trade datasheets are written for a buyer who will ask for one. A retail tin aimed at a weekend job doesn't always get the same treatment, and nothing published so far settles whether that's changing.
Searching a manufacturer's own site for the term isn't a reliable way to check on its own. A search box that returns nothing for a word known to appear elsewhere on that same site has failed its own control, and that's the result a check along those lines actually produced. It tells you the search is unreliable, not that the figure doesn't exist somewhere on the site.
Until that gap is closed, the surer route is to ask the supplier directly. Who publishes figures at all, and who sells rather than tests, is covered on Who Publishes What and Who Pays.
What to ask a manufacturer
A Pendulum Test Value on its own does not tell you whether a surface will be slippery once it is wet. The figure only means something when you know the conditions it was measured under: wet or dry, which substrate, and which rubber slider was fitted to the pendulum. Put those together into one question and a manufacturer either has an answer or they do not.
Wet, not dry
A Pendulum Test Value (PTV) measures how much grip a rubber slider finds on a surface as a weighted arm swings across it. A dry result and a wet result for the same coating can sit in different bands, because water changes how the slider contacts the surface. Ask for the wet figure specifically, since that is the condition a patio or path actually meets in rain or after a hose.
Your substrate, not a lab floor
The same paint can behave differently depending on what it is sitting on. A substrate is simply the material underneath the coating, and dense concrete, natural stone, cement render and lime render all take paint differently. A PTV measured on one tells you little about the others, so name the one you have, whether it is concrete, natural stone, cement render or lime render, when you ask.
The test method and the slider
BS 7976-2 is the British Standard that sets out how a pendulum test is carried out. Within that standard, the result still depends on which rubber slider was fitted, because different sliders are used for different kinds of surface and can give different readings on the same patch of paving. A figure quoted without the standard and the slider is a number with no way to check what it describes.
Those conditions fit into one sentence to send a manufacturer. What is the wet PTV of this product on my substrate, tested to BS 7976-2, and with which slider? A manufacturer who can answer all four parts has given you something you can compare, and one who cannot has told you that too.