Are porcelain slabs
actually slippery?
It is the question we get asked more than any other, usually by someone who has seen shiny porcelain in a bathroom and assumed the patio version is the same thing. It is not.
External porcelain rated R11 grips well in the wet. The paving that causes accidents in this country is almost never the wrong slab. It is the right slab with two years of algae on it.
Indoor porcelain and outdoor porcelain are not the same product
This is where the reputation comes from. Indoor floor tiles are often polished, 8 to 10mm thick and rated around R9. Outdoor paving porcelain is 20mm, unpolished, and carries a deliberately textured face. Same material family, completely different surface. If someone tells you their porcelain patio is treacherous in the rain, there is a fair chance an indoor tile was laid outside.
What the ratings mean in plain terms
| Rating | Ramp angle | Typically used for |
|---|---|---|
| R9 | 6 to 10 degrees | Indoor dry areas |
| R10 | 10 to 19 degrees | Indoor wet areas, entrances |
| R11 | 19 to 27 degrees | External paving, commercial kitchens |
| R12 | 27 to 35 degrees | Industrial floors, heavy wet use |
Our porcelain range is R11. For context, a patio should be laid with a fall of roughly 1 in 80 for drainage, which is well under a single degree.
The real cause of slippery paving
Organic growth. Algae, lichen and moss build up on any surface that stays damp and shaded, and once there is a film of it the slab underneath stops mattering. North-facing patios, ground under trees and anywhere water sits after rain are the usual spots.
Two things prevent it, and neither is exotic. Get the falls right so water leaves the surface instead of pooling, and wash the patio once a year with a pH neutral cleaner. Porcelain has the edge here because it is non-porous, so growth sits on top rather than getting a grip in the pores, and it comes off with far less effort.
What to ask a supplier
- Is this an external grade slab, and what thickness is it?
- What is the slip rating, and to which standard?
- Is the face polished, textured or riven?
- Is there a higher grip option for steps and pool surrounds?
Any supplier worth buying from will answer all four without hesitating. If the answer to the second one is vague, that tells you something.
Are porcelain paving slabs slippery when wet?
External porcelain rated R11 is not slippery in normal wet conditions. It is the same category of rating used for commercial kitchens and workshop floors. What catches people out is indoor porcelain used outside, which is a different product with a smooth polished face.
What does R11 mean?
R11 is a slip rating from the German standard DIN 51130. A tester walks an oiled ramp in the surface being tested and the ramp is tilted until they slip. R9 is the lowest of the practical grades, R13 the highest. R11 means slipping started somewhere between 19 and 27 degrees, which is comfortably beyond anything a patio should ever be laid at.
Is porcelain more or less slippery than Indian sandstone?
Dry, there is very little in it. Wet, riven sandstone has a natural texture working in its favour, while R11 porcelain relies on an engineered surface texture. Both perform fine. The difference shows up over time: sandstone can build up algae in shade, and algae is what actually makes paving slippery.
What is PTV and how does it relate to R ratings?
PTV is the pendulum test value, the measure used more commonly in the UK. Above 36 is classed as a low slip risk. R ratings and PTV are separate tests and do not convert cleanly between each other, so a supplier quoting one is not withholding the other on purpose.
Do I need a special finish for a poolside or a slope?
For pool surrounds, steps and anything with a noticeable gradient, ask specifically for the highest textured finish in the range rather than assuming the standard patio slab is right. Grip matters more the moment the surface is not flat.
Tell us what you need and we'll price it.
Send over your area in square metres and we'll come back with availability, pack sizes and a quote.