Short answer: Plain smooth glass is slippery when wet, but walk-on glass is not supplied plain. For outdoor use the top surface is fritted or etched so it grips under a shoe, and the maker publishes standard-test slip resistance figures for each finish. For walk-on glass slip resistance, ask for the tested figure for the exact panel going on your roof.
Why ordinary glass slides and walk-on glass does not
A pane of float glass is almost perfectly smooth. Add a film of rain, a smear of moss or a wet sole, and there is nothing for the shoe to bite on.
Walk-on glass for a floor or terrace is made differently from a window pane. The top layer is treated so the surface has texture, and the texture is part of the product. Anti-slip rooflight glass comes in two treatments, described below, and both stay clear enough to pass daylight to the room underneath.
For the full picture of what a walk-on unit is and where it goes, start at our walk-on rooflight installation page. This page covers grip only. How the glass is laminated to carry a person is in the guide on load ratings and glass build-ups.
The two surface finishes: fritted and etched
Fritted glass has a ceramic pattern fired onto the top surface. The pattern is usually a field of small dots or a fine grid, and it is baked in during manufacture so it becomes part of the glass rather than a coating that wears off. The dots stand slightly proud. A shoe rests on them and the water in between runs off.
Etched glass is roughened instead. A sandblast or an acid treatment removes a very thin layer and leaves a matt, slightly gritty face. The texture is even across the whole panel, so the look is a soft, frosted one, and the grip does not depend on a pattern of dots. Light still passes through, though the view down is blurred.
A few points help when you compare the two:
- Fritted panels carry a pattern you can see, so pick the dot size with the room below in mind
- Etched panels look frosted, which keeps privacy for a basement or bathroom
- The finish sits on the walking surface, never on the underside
- Ask which finish the tested figure belongs to
How slip resistance is measured
Grip is not a matter of opinion. Two laboratory methods dominate in Britain, and a decent data sheet quotes one or both.
The pendulum test swings a rubber slider across a wetted sample and records how much the surface slows it. The result is a pendulum test value, and a higher value means more grip.
The ramp test puts a person on a sloping, oiled sample and tilts it until they slip, and the angle sets a rating band. It was developed for workplaces where oil is on the floor, so it is a tough test. Makers of walk-on glass who publish a ramp rating are showing the grip on a worst-case surface.
| Test | What it does | Reads as |
|---|---|---|
| Pendulum | Rubber slider over a wet sample | A pendulum value |
| Ramp | Person walks on an oiled, tilting sample | A rating band |
We do not quote a number on this page, because the figure belongs to a specific finish from a specific maker, and it changes if the maker changes the pattern. What we do is read the data sheet for the panel on your quote and show it to you before the glass is ordered.
Where grip matters most
An internal floor panel in a dry hallway puts few demands on the surface. Outdoors the picture changes, and a few places on Merseyside homes need the most care.
Roof terraces and balconies. Rain from the west falls on a terrace many days of the year, and wind blows it flat across the glass. A terrace panel is wet for much of the year, so a tested outdoor finish is a requirement, not a nicety. Our page on walk-on rooflights on a roof terrace covers how the panel sits within the deck.
Lightwells and front paths. Many Victorian and Edwardian terraces have a cellar below the pavement or a lightwell at the front. Glass set in a path or a yard collects leaf litter and damp from the shade of the house. A panel here sits in the open and is the one most likely to hold moss through the winter.
Keeping the grip you paid for
A tested finish is a starting point. Moss, algae and grime reduce the grip of any outdoor surface, so a panel that is never cleaned feels different in January from the day it was fitted.
Wash it with a soft brush, warm water and a mild detergent. Avoid hard tools, abrasive pads and strong acids, which can mark glass and dull the very texture that gives the grip.
We pass on the maker's cleaning guidance at handover, in writing, alongside the guarantee paperwork. Our survey also looks at where the panel sits, how it falls and whether the surround drains, since a panel that holds standing water is the one that goes green first. The panel finish is named in the fixed written quote we give you, and the installation itself is guaranteed for 10 years in writing. Get a free quote
Grip on glass: what comes up at survey
Can I add an anti-slip finish to glass already in the floor?
Not usefully. The treatment is part of the glass, made in the factory before the panel is laminated. A surface coating or tape on top of an existing panel is not a substitute and can trap dirt, so a poor-gripping panel is normally replaced with one that has the proper finish.
Is a frosted look the same as a slip-resistant surface?
No. Glass can be frosted on the underside purely for privacy, and that does nothing for the sole of a shoe. The grip comes from a texture or pattern on the face you walk on, so we always confirm which face carries the finish.
Will a fritted pattern be noticeable from the room below?
You will see it, because the dots are part of what lights the room, but it reads as a soft pattern against the sky rather than as an obstruction. If the view up matters more than the grip, an etched panel gives a plainer frosted look. We can show you both finishes on a sample before you choose.