Low-E and tinted coatings scratch far more easily than plain glass, and self-cleaning coatings can be stripped by abrasive pads. In 2026, always confirm the coating type before choosing a brush, and never use a stiff bristle on any soft-coat surface.
A cleaner put a standard brush on a low-E roof and left a faint swirl pattern visible only at grazing sun angles. The client noticed within a week. Nobody could undo it. Coating type decides what the robot is allowed to touch.
How do the coating types differ?
| Glass type | Surface | Robot care |
|---|---|---|
| Plain float glass | hard | any pad or brush |
| Hard-coat low-E | moderate | soft brush, low pressure |
| Soft-coat low-E | fragile | microfibre pad only |
| Tinted body glass | hard | avoid heat and thermal shock |
| Self-cleaning (hydrophilic) | coating layer | no abrasives, water only |
Soft-coat low-E is the one that catches people. It has a thin silver-based layer that can be damaged by friction. It usually sits on an inner pane, which is a saving grace, because a robot cleans the outer face. But some laminated builds expose it, and then a stiff brush is a mistake.
What breaks a self-cleaning coating?
Self-cleaning glass has a photocatalytic layer that breaks down organic dirt, plus a hydrophilic property so rain sheets off. Abrasive brushes and strong chemicals remove that layer. Once gone, the glass dirties faster than untreated glass because the mechanism is gone but the roughened surface holds grime. If you have self-cleaning glass, use water and a soft pad, and tell the operator why.
Does heat matter on tinted glass?
Yes, and it is often missed. Tinted and coated glass absorbs more solar energy, so surface temperatures on a sunny day can run 15-20 degrees C above ambient. Pouring cold water onto 55-degree glass risks thermal shock and, in rare cases, cracking. Clean tinted or coated glass before 10:00 or after 16:00, or cool it with a light mist first. Our background on thermal shock on hot glass explains the mechanism.
What should you write into the method statement?
- Named glass type per roof zone, taken from the original spec, not guessed.
- Approved pad or brush per type, with a photo of the packaging.
- Max surface temperature for cleaning, usually under 40 degrees C.
- Chemical list, since solvents can haze coatings.
- Who signs off if the coating type cannot be confirmed.
Who should pause before cleaning coated glass?
Anyone who cannot confirm the coating. If the building is new and the specification is available, fine. If the glass was replaced by a contractor with no paperwork, test a small edge pane first or use the softest method you have. The cost of a cautious clean is small; the cost of a scratched coated facade is a replace-the-panes conversation.
How do you identify a coating in the field?
Start with the specification, then confirm against the build. A low-E pane usually carries a faint colour tint when viewed at an angle and will look different in reflected light from a plain pane beside it. If no paperwork exists, a small edge pane and a test pass with your softest pad is the safe route. Never guess on a visible facade.
Self-cleaning glass is easier to spot: water beads and sheets off differently, and the surface usually feels slick. If a pane that used to shed water suddenly holds droplets after a cleaning, you may already have stripped the coating.
Which chemicals are safe on coated glass?
Mild pH-neutral cleaner is the default. Avoid ammonia on soft-coat surfaces, avoid abrasives of any kind, and avoid strong acids on tinted glass with metallic films. On self-cleaning glass, water alone is best. If a client insists on a branded product, check its SDS against the coating spec before it touches the pane.
What does a scratch actually cost?
A single scratched coated pane on a large roof is not a cleaning bill, it is a glazing replacement. On a big coated installation, replacing one unit can run into four figures once access, matching the tint batch and labour are counted. That is the real reason to slow down on coated glass. The robot is perfectly capable of cleaning it well; it is also perfectly capable of doing damage fast if the pad is wrong.
What about laminated and double-skin glass?
Laminated glass has a plastic interlayer, but you clean the outer pane, so the interlayer only matters if the edge is exposed. Double-skin and triple-skin roofs are the real issue, because the coating often sits on an inner pane and the cavity can trap moisture. On those, cleaning the outer face is safe, but never open or probe the cavity, and never use a pressure jet at the perimeter seal.
If a double-skin unit shows internal condensation, that is a failed seal, not a cleaning defect. Report it to the client rather than trying to clean it away.
One last point on coated glass: document what you used. A short log of pad type, chemical and date per facade turns a coating dispute into a record. If a client later claims damage, the log is what protects both sides.
Key Takeaways
- Soft-coat low-E requires microfibre only; stiff brushes cause permanent marks.
- Self-cleaning coatings are destroyed by abrasives, then the glass dirties faster.
- Tinted and coated glass runs 15-20 degrees C above ambient; avoid cold-water shock.
- Write glass type, approved pad, and max temperature into the method statement.
- If coating type is unconfirmed, test one pane before a full run.