Tile lines and waterline surfaces: what a robot can reach

The waterline is the strip of wall where the water meets the air. It's where oils, sunscreen and mineral scale tend to collect. A robot that cleans the floor well may still leave a band there. The reason is partly the robot and partly the surface.

Why the band is hard

A maker says the tile waterline band collects calcium buildup, sunscreen and oil residue.¹ Another says residue tends to collect in the transition areas of a textured pool, so wall grip and waterline consistency matter.² That's a stubborn film, and a robot passing quickly may not lift it.

Then there's reach. A robot has to climb to get there. On rough concrete, one maker warns, a cleaner with weak grip can slide back down before it arrives there.³ Check your own manual for whether the robot cleans the waterline, and don't assume it does if the manual is silent.

Pools with a different finish above and below the water add another wrinkle. A smooth tile band can feel different to a robot than the plaster or liner beneath it. One maker notes that a cleaner that works well on one tile surface may perform differently on another, because texture and adhesion differ.⁴

Tile and grout

Tile is smooth, but the joints between tiles aren't. One maker says grout lines can collect dirt and algae.⁴ Another says grout lines trap debris and algae.¹ A brush has to reach into those lines.

Climbing tile is its own question. A maker says tile walls may give different levels of traction depending on the tile finish and the water conditions.⁴ A robot that grips one tiled pool may behave differently in another.

Coping, the edge above the tile

Coping is the cap along the top of the pool wall. In a vinyl liner pool, a builder describes the liner as hung from a coping retainer track mounted at the top of the wall.⁵ Check your own manual for whether the robot cleans the waterline.

What you can do

• Check whether your robot's manual lists waterline cleaning.- Look at the band after a run. A film left behind can mean the robot didn't reach it, or didn't scrub it well enough.
• Follow your product's manual for any hand cleaning of tile. For chemicals or descaling products, follow the label of the product maker, and don't mix products.
• Check parked-at-the-edge behaviour in the manual, so the robot isn't left stuck at the waterline.

For how the grip story changes by finish, read the pages on rough plaster and pebble. For the starting ideas, there's a short explainer on finishes.

Only run it with the pool empty of people. The manual's power supply rules near water apply too.